From 0d7b986da6fb2d88ba150418b88b7c39a928f103 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Mon, 12 Jul 2021 14:23:02 +0200
Subject: [PATCH 01/18] Make solo half of split keyboards (more) usable.

Using only one half of a split keyboard (that's using the split_common
framework to communicate) is not a great experience, since several read
timeouts per scan cycle cause an unusably slow scan rate.

This change blocks all split communication attempts for 500 ms
(configurable) after an error occurs, causing the scan rate to become at
least _more_ usable, but might need some tweaking to work fully on most
keyboards. One read timeout still needs to occur after the 500 ms has
passed, and if that timeout isn't low enough, some scan cycles may still
be too slow.
---
 quantum/split_common/transactions.c | 30 +++++++++++++++++++++++++++--
 1 file changed, 28 insertions(+), 2 deletions(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index abad626e0022..7ab263845006 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -31,6 +31,10 @@
 #    define FORCED_SYNC_THROTTLE_MS 100
 #endif  // FORCED_SYNC_THROTTLE_MS
 
+#ifndef SYNC_CONNECTION_CHECK_TIMEOUT
+#    define SYNC_CONNECTION_CHECK_TIMEOUT 500
+#endif
+
 #define sizeof_member(type, member) sizeof(((type *)NULL)->member)
 
 #define trans_initiator2target_initializer_cb(member, cb) \
@@ -41,8 +45,8 @@
     { &dummy, 0, 0, sizeof_member(split_shared_memory_t, member), offsetof(split_shared_memory_t, member), cb }
 #define trans_target2initiator_initializer(member) trans_target2initiator_initializer_cb(member, NULL)
 
-#define transport_write(id, data, length) transport_execute_transaction(id, data, length, NULL, 0)
-#define transport_read(id, data, length) transport_execute_transaction(id, NULL, 0, data, length)
+#define transport_write(id, data, length) transport_transaction(id, data, length, NULL, 0)
+#define transport_read(id, data, length) transport_transaction(id, NULL, 0, data, length)
 
 #if defined(SPLIT_TRANSACTION_IDS_KB) || defined(SPLIT_TRANSACTION_IDS_USER)
 // Forward-declare the RPC callback handlers
@@ -53,6 +57,28 @@ void slave_rpc_exec_callback(uint8_t initiator2target_buffer_size, const void *i
 ////////////////////////////////////////////////////
 // Helpers
 
+bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
+    // Throttle transaction attempts if target isn't connected
+    // Without this, a solo half becomes unusable due to constant read timeouts
+    static bool target_connected = true;
+    static uint16_t connection_check_timer = 0;
+    if (!target_connected && timer_elapsed(connection_check_timer) < SYNC_CONNECTION_CHECK_TIMEOUT) {
+        return false;
+    }
+    connection_check_timer = timer_read();
+
+    if (!transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length)) {
+        target_connected = false;
+        dprintln("Target disconnected, throttling connection attempts");
+        return false;
+    } else if (!target_connected) {
+        dprintln("Target connected");
+    }
+
+    target_connected = true;
+    return true;
+}
+
 bool transaction_handler_master(bool okay, matrix_row_t master_matrix[], matrix_row_t slave_matrix[], const char *prefix, bool (*handler)(matrix_row_t master_matrix[], matrix_row_t slave_matrix[])) {
     if (okay) {
         bool this_okay = true;

From 13a70f360c34efa9d2058a6d4f2c2289145a643f Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Mon, 12 Jul 2021 15:00:49 +0200
Subject: [PATCH 02/18] Fix lint complaint.

---
 quantum/split_common/transactions.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index 7ab263845006..2a44fb3f1291 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -60,7 +60,7 @@ void slave_rpc_exec_callback(uint8_t initiator2target_buffer_size, const void *i
 bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
     // Throttle transaction attempts if target isn't connected
     // Without this, a solo half becomes unusable due to constant read timeouts
-    static bool target_connected = true;
+    static bool     target_connected       = true;
     static uint16_t connection_check_timer = 0;
     if (!target_connected && timer_elapsed(connection_check_timer) < SYNC_CONNECTION_CHECK_TIMEOUT) {
         return false;

From ea0f56834c28cf2e883c72326958ef1b8d217961 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Mon, 12 Jul 2021 20:31:00 +0200
Subject: [PATCH 03/18] Require 25 consecutive comm errors to see comms as
 disconnected.

The number of max errors can be overridden by defining
`SPLIT_MAX_CONNECTION_ERRORS`.
---
 quantum/split_common/transactions.c | 26 +++++++++++++++++---------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index 2a44fb3f1291..dc8443621300 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -31,9 +31,13 @@
 #    define FORCED_SYNC_THROTTLE_MS 100
 #endif  // FORCED_SYNC_THROTTLE_MS
 
-#ifndef SYNC_CONNECTION_CHECK_TIMEOUT
-#    define SYNC_CONNECTION_CHECK_TIMEOUT 500
-#endif
+#ifndef SPLIT_MAX_CONNECTION_ERRORS
+#    define SPLIT_MAX_CONNECTION_ERRORS 25
+#endif  // SPLIT_MAX_CONNECTION_ERRORS
+
+#ifndef SPLIT_CONNECTION_CHECK_TIMEOUT
+#    define SPLIT_CONNECTION_CHECK_TIMEOUT 500
+#endif  // SPLIT_CONNECTION_CHECK_TIMEOUT
 
 #define sizeof_member(type, member) sizeof(((type *)NULL)->member)
 
@@ -60,22 +64,26 @@ void slave_rpc_exec_callback(uint8_t initiator2target_buffer_size, const void *i
 bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
     // Throttle transaction attempts if target isn't connected
     // Without this, a solo half becomes unusable due to constant read timeouts
-    static bool     target_connected       = true;
+    static uint8_t  connection_errors      = 0;
     static uint16_t connection_check_timer = 0;
-    if (!target_connected && timer_elapsed(connection_check_timer) < SYNC_CONNECTION_CHECK_TIMEOUT) {
+    if (connection_errors >= SPLIT_MAX_CONNECTION_ERRORS && timer_elapsed(connection_check_timer) < SPLIT_CONNECTION_CHECK_TIMEOUT) {
         return false;
     }
     connection_check_timer = timer_read();
 
     if (!transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length)) {
-        target_connected = false;
-        dprintln("Target disconnected, throttling connection attempts");
+        if (connection_errors < UINT8_MAX) {
+            connection_errors++;
+        }
+        if (connection_errors >= SPLIT_MAX_CONNECTION_ERRORS) {
+            dprintln("Target disconnected, throttling connection attempts");
+        }
         return false;
-    } else if (!target_connected) {
+    } else if (connection_errors >= SPLIT_MAX_CONNECTION_ERRORS) {
         dprintln("Target connected");
     }
 
-    target_connected = true;
+    connection_errors = 0;
     return true;
 }
 

From 0701839a797bc49103e669e5b6949534fb2bff33 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Mon, 12 Jul 2021 21:16:28 +0200
Subject: [PATCH 04/18] Add comments to new defines, and ability to disable
 disconnection check.

Also increase `SPLIT_MAX_CONNECTION_ERRORS` to 40, since it's divisible
by most relevant numbers for the description.
---
 quantum/split_common/transactions.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index dc8443621300..c37bdf7a8f05 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -31,10 +31,16 @@
 #    define FORCED_SYNC_THROTTLE_MS 100
 #endif  // FORCED_SYNC_THROTTLE_MS
 
+// Max number of consecutive failed communications before the communication is seen as disconnected.
+// All built-in transactions (i.e. not transaction_rpc_*-based ones) are given 10 attempts each, and most send one transaction over the transport, so 40 errors is basically (up to) four completely failed built-in transactions.
+// On the other hand, each RPC transaction consists of four transport transactions without retries, so 40 errors is roughly ten completely failed RPC transactions.
+// Set to a negative value to disable the disconnection check altogether.
 #ifndef SPLIT_MAX_CONNECTION_ERRORS
-#    define SPLIT_MAX_CONNECTION_ERRORS 25
+#    define SPLIT_MAX_CONNECTION_ERRORS 40
 #endif  // SPLIT_MAX_CONNECTION_ERRORS
 
+// How long (in milliseconds) to block all connection attempts after the communication has been flagged as disconnected.
+// Each [this amount of time], one connection attempt will be allowed. If that succeeds, the communication is seen as up again.
 #ifndef SPLIT_CONNECTION_CHECK_TIMEOUT
 #    define SPLIT_CONNECTION_CHECK_TIMEOUT 500
 #endif  // SPLIT_CONNECTION_CHECK_TIMEOUT
@@ -62,7 +68,10 @@ void slave_rpc_exec_callback(uint8_t initiator2target_buffer_size, const void *i
 // Helpers
 
 bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
-    // Throttle transaction attempts if target isn't connected
+#if SPLIT_MAX_CONNECTION_ERRORS < 0
+    return transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length);
+#else  // SPLIT_MAX_CONNECTION_ERRORS < 0
+    // Throttle transaction attempts if target doesn't seem to be connected
     // Without this, a solo half becomes unusable due to constant read timeouts
     static uint8_t  connection_errors      = 0;
     static uint16_t connection_check_timer = 0;
@@ -85,6 +94,7 @@ bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t
 
     connection_errors = 0;
     return true;
+#endif  // SPLIT_MAX_CONNECTION_ERRORS < 0
 }
 
 bool transaction_handler_master(bool okay, matrix_row_t master_matrix[], matrix_row_t slave_matrix[], const char *prefix, bool (*handler)(matrix_row_t master_matrix[], matrix_row_t slave_matrix[])) {

From 1d1ce1b69895bcd89a7abf4551e541f468451d79 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Mon, 12 Jul 2021 21:22:28 +0200
Subject: [PATCH 05/18] Make lint happy ...again

---
 quantum/split_common/transactions.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index c37bdf7a8f05..2e5bb40716d2 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -70,7 +70,7 @@ void slave_rpc_exec_callback(uint8_t initiator2target_buffer_size, const void *i
 bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
 #if SPLIT_MAX_CONNECTION_ERRORS < 0
     return transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length);
-#else  // SPLIT_MAX_CONNECTION_ERRORS < 0
+#else   // SPLIT_MAX_CONNECTION_ERRORS < 0
     // Throttle transaction attempts if target doesn't seem to be connected
     // Without this, a solo half becomes unusable due to constant read timeouts
     static uint8_t  connection_errors      = 0;

From 1e1fb268bf603801fa346e6f96f7b5f3bab8a232 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Mon, 12 Jul 2021 22:27:08 +0200
Subject: [PATCH 06/18] Only update `connection_check_timer` when needed.

---
 quantum/split_common/transactions.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index 2e5bb40716d2..eec1750a37e6 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -78,13 +78,13 @@ bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t
     if (connection_errors >= SPLIT_MAX_CONNECTION_ERRORS && timer_elapsed(connection_check_timer) < SPLIT_CONNECTION_CHECK_TIMEOUT) {
         return false;
     }
-    connection_check_timer = timer_read();
 
     if (!transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length)) {
         if (connection_errors < UINT8_MAX) {
             connection_errors++;
         }
         if (connection_errors >= SPLIT_MAX_CONNECTION_ERRORS) {
+            connection_check_timer = timer_read();
             dprintln("Target disconnected, throttling connection attempts");
         }
         return false;

From a53745799f70130a7e86811746a2a14f9e38c83f Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Mon, 12 Jul 2021 22:27:38 +0200
Subject: [PATCH 07/18] Add new defines to split keyboard documentation.

---
 docs/feature_split_keyboard.md      | 14 ++++++++++++++
 quantum/split_common/transactions.c |  2 +-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/docs/feature_split_keyboard.md b/docs/feature_split_keyboard.md
index 428d581cab6c..34fe29546eaf 100644
--- a/docs/feature_split_keyboard.md
+++ b/docs/feature_split_keyboard.md
@@ -203,6 +203,20 @@ If you're having issues with serial communication, you can change this value, as
 
 This sets the maximum number of milliseconds before forcing a synchronization of data from master to slave. Under normal circumstances this sync occurs whenever the data _changes_, for safety a data transfer occurs after this number of milliseconds if no change has been detected since the last sync. 
 
+```c
+#define SPLIT_MAX_CONNECTION_ERRORS 40
+```
+This sets the maximum number of failed communication attempts from the master part before it assumes that no slave part is connected. This makes it possible to use a master part without the slave part connected.
+
+All built-in transactions (i.e. not `transaction_rpc_*`-based ones) are given 10 attempts each, and most send one transaction each over the transport, so 40 errors is basically (up to) four completely failed built-in transactions. On the other hand, each RPC transaction consists of four transport transactions without retries, so 40 errors is roughly ten completely failed RPC transactions. Setting it to a negative value will disable the disconnection check altogether.
+
+```c
+#define SPLIT_CONNECTION_CHECK_TIMEOUT 500
+```
+How long (in milliseconds) the master part should block all connection attempts to the slave after the communication has been flagged as disconnected (see `SPLIT_MAX_CONNECTION_ERRORS` above).
+
+One communication attempt will be allowed everytime this amount of time has passed since the last attempt. If that attempt succeeds, the communication is seen as working again.
+
 ```c
 #define SPLIT_TRANSPORT_MIRROR
 ```
diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index eec1750a37e6..9b931e73dac4 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -40,7 +40,7 @@
 #endif  // SPLIT_MAX_CONNECTION_ERRORS
 
 // How long (in milliseconds) to block all connection attempts after the communication has been flagged as disconnected.
-// Each [this amount of time], one connection attempt will be allowed. If that succeeds, the communication is seen as up again.
+// One communication attempt will be allowed everytime this amount of time has passed since the last attempt. If that attempt succeeds, the communication is seen as working again.
 #ifndef SPLIT_CONNECTION_CHECK_TIMEOUT
 #    define SPLIT_CONNECTION_CHECK_TIMEOUT 500
 #endif  // SPLIT_CONNECTION_CHECK_TIMEOUT

From 1b0d82ba4da40e61c4f6d0f38afa90371ccf16f6 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Tue, 3 Aug 2021 18:07:34 +0200
Subject: [PATCH 08/18] Move connection timeout logic to transport.c, add
 `is_transport_connected`.

---
 quantum/split_common/transactions.c | 44 ------------------------
 quantum/split_common/transport.c    | 53 +++++++++++++++++++++++++++--
 quantum/split_common/transport.h    |  4 ++-
 3 files changed, 53 insertions(+), 48 deletions(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index 9b931e73dac4..0c9c906ed4e9 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -31,20 +31,6 @@
 #    define FORCED_SYNC_THROTTLE_MS 100
 #endif  // FORCED_SYNC_THROTTLE_MS
 
-// Max number of consecutive failed communications before the communication is seen as disconnected.
-// All built-in transactions (i.e. not transaction_rpc_*-based ones) are given 10 attempts each, and most send one transaction over the transport, so 40 errors is basically (up to) four completely failed built-in transactions.
-// On the other hand, each RPC transaction consists of four transport transactions without retries, so 40 errors is roughly ten completely failed RPC transactions.
-// Set to a negative value to disable the disconnection check altogether.
-#ifndef SPLIT_MAX_CONNECTION_ERRORS
-#    define SPLIT_MAX_CONNECTION_ERRORS 40
-#endif  // SPLIT_MAX_CONNECTION_ERRORS
-
-// How long (in milliseconds) to block all connection attempts after the communication has been flagged as disconnected.
-// One communication attempt will be allowed everytime this amount of time has passed since the last attempt. If that attempt succeeds, the communication is seen as working again.
-#ifndef SPLIT_CONNECTION_CHECK_TIMEOUT
-#    define SPLIT_CONNECTION_CHECK_TIMEOUT 500
-#endif  // SPLIT_CONNECTION_CHECK_TIMEOUT
-
 #define sizeof_member(type, member) sizeof(((type *)NULL)->member)
 
 #define trans_initiator2target_initializer_cb(member, cb) \
@@ -67,36 +53,6 @@ void slave_rpc_exec_callback(uint8_t initiator2target_buffer_size, const void *i
 ////////////////////////////////////////////////////
 // Helpers
 
-bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
-#if SPLIT_MAX_CONNECTION_ERRORS < 0
-    return transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length);
-#else   // SPLIT_MAX_CONNECTION_ERRORS < 0
-    // Throttle transaction attempts if target doesn't seem to be connected
-    // Without this, a solo half becomes unusable due to constant read timeouts
-    static uint8_t  connection_errors      = 0;
-    static uint16_t connection_check_timer = 0;
-    if (connection_errors >= SPLIT_MAX_CONNECTION_ERRORS && timer_elapsed(connection_check_timer) < SPLIT_CONNECTION_CHECK_TIMEOUT) {
-        return false;
-    }
-
-    if (!transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length)) {
-        if (connection_errors < UINT8_MAX) {
-            connection_errors++;
-        }
-        if (connection_errors >= SPLIT_MAX_CONNECTION_ERRORS) {
-            connection_check_timer = timer_read();
-            dprintln("Target disconnected, throttling connection attempts");
-        }
-        return false;
-    } else if (connection_errors >= SPLIT_MAX_CONNECTION_ERRORS) {
-        dprintln("Target connected");
-    }
-
-    connection_errors = 0;
-    return true;
-#endif  // SPLIT_MAX_CONNECTION_ERRORS < 0
-}
-
 bool transaction_handler_master(bool okay, matrix_row_t master_matrix[], matrix_row_t slave_matrix[], const char *prefix, bool (*handler)(matrix_row_t master_matrix[], matrix_row_t slave_matrix[])) {
     if (okay) {
         bool this_okay = true;
diff --git a/quantum/split_common/transport.c b/quantum/split_common/transport.c
index a711ef85f056..6c9da2797ebf 100644
--- a/quantum/split_common/transport.c
+++ b/quantum/split_common/transport.c
@@ -22,6 +22,22 @@
 #include "transaction_id_define.h"
 #include "atomic_util.h"
 
+// Max number of consecutive failed communications before the communication is seen as disconnected.
+// All built-in transactions (i.e. not transaction_rpc_*-based ones) are given 10 attempts each, and most send one transaction over the transport, so 40 errors is basically (up to) four completely failed built-in transactions.
+// On the other hand, each RPC transaction consists of four transport transactions without retries, so 40 errors is roughly ten completely failed RPC transactions.
+// Set to a negative value to disable the disconnection check altogether.
+#ifndef SPLIT_MAX_CONNECTION_ERRORS
+#    define SPLIT_MAX_CONNECTION_ERRORS 40
+#endif  // SPLIT_MAX_CONNECTION_ERRORS
+
+// How long (in milliseconds) to block all connection attempts after the communication has been flagged as disconnected.
+// One communication attempt will be allowed everytime this amount of time has passed since the last attempt. If that attempt succeeds, the communication is seen as working again.
+#ifndef SPLIT_CONNECTION_CHECK_TIMEOUT
+#    define SPLIT_CONNECTION_CHECK_TIMEOUT 500
+#endif  // SPLIT_CONNECTION_CHECK_TIMEOUT
+
+static uint8_t connection_errors = 0;
+
 #ifdef USE_I2C
 
 #    ifndef SLAVE_I2C_TIMEOUT
@@ -55,7 +71,7 @@ i2c_status_t transport_trigger_callback(int8_t id) {
     return i2c_writeReg(SLAVE_I2C_ADDRESS, trans->initiator2target_offset, split_trans_initiator2target_buffer(trans), trans->initiator2target_buffer_size, SLAVE_I2C_TIMEOUT);
 }
 
-bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
+static bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
     i2c_status_t              status;
     split_transaction_desc_t *trans = &split_transaction_table[id];
     if (initiator2target_length > 0) {
@@ -92,7 +108,7 @@ split_shared_memory_t *const split_shmem = &shared_memory;
 void transport_master_init(void) { soft_serial_initiator_init(); }
 void transport_slave_init(void) { soft_serial_target_init(); }
 
-bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
+static bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
     split_transaction_desc_t *trans = &split_transaction_table[id];
     if (initiator2target_length > 0) {
         size_t len = trans->initiator2target_buffer_size < initiator2target_length ? trans->initiator2target_buffer_size : initiator2target_length;
@@ -115,4 +131,35 @@ bool transport_execute_transaction(int8_t id, const void *initiator2target_buf,
 
 bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { return transactions_master(master_matrix, slave_matrix); }
 
-void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { transactions_slave(master_matrix, slave_matrix); }
\ No newline at end of file
+void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { transactions_slave(master_matrix, slave_matrix); }
+
+bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
+#if SPLIT_MAX_CONNECTION_ERRORS < 0
+    return transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length);
+#else   // SPLIT_MAX_CONNECTION_ERRORS < 0
+    // Throttle transaction attempts if target doesn't seem to be connected
+    // Without this, a solo half becomes unusable due to constant read timeouts
+    static uint16_t connection_check_timer = 0;
+    if (!is_transport_connected() && timer_elapsed(connection_check_timer) < SPLIT_CONNECTION_CHECK_TIMEOUT) {
+        return false;
+    }
+
+    if (!transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length)) {
+        if (connection_errors < UINT8_MAX) {
+            connection_errors++;
+        }
+        if (!is_transport_connected()) {
+            connection_check_timer = timer_read();
+            dprintln("Target disconnected, throttling connection attempts");
+        }
+        return false;
+    } else if (!is_transport_connected()) {
+        dprintln("Target connected");
+    }
+
+    connection_errors = 0;
+    return true;
+#endif  // SPLIT_MAX_CONNECTION_ERRORS < 0
+}
+
+bool is_transport_connected(void) { return connection_errors < SPLIT_MAX_CONNECTION_ERRORS; }
diff --git a/quantum/split_common/transport.h b/quantum/split_common/transport.h
index 2e07f6b25cf9..9d219874a029 100644
--- a/quantum/split_common/transport.h
+++ b/quantum/split_common/transport.h
@@ -38,7 +38,9 @@ void transport_slave_init(void);
 bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]);
 void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]);
 
-bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length);
+bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length);
+
+bool is_transport_connected(void);
 
 #ifdef ENCODER_ENABLE
 #    include "encoder.h"

From 7e5ce483f0805b0b18a85123d79f45fbe95159db Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Tue, 3 Aug 2021 18:09:16 +0200
Subject: [PATCH 09/18] Use split_common disconnection logic in matrix.c.

Instead of doing more or less the same thing twice.
---
 quantum/matrix.c | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/quantum/matrix.c b/quantum/matrix.c
index d22817bf48ed..49784a987dc7 100644
--- a/quantum/matrix.c
+++ b/quantum/matrix.c
@@ -25,10 +25,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #    include "split_common/split_util.h"
 #    include "split_common/transactions.h"
 
-#    ifndef ERROR_DISCONNECT_COUNT
-#        define ERROR_DISCONNECT_COUNT 5
-#    endif  // ERROR_DISCONNECT_COUNT
-
 #    define ROWS_PER_HAND (MATRIX_ROWS / 2)
 #else
 #    define ROWS_PER_HAND (MATRIX_ROWS)
@@ -310,13 +306,9 @@ void matrix_init(void) {
 bool matrix_post_scan(void) {
     bool changed = false;
     if (is_keyboard_master()) {
-        static uint8_t error_count;
-
         matrix_row_t slave_matrix[ROWS_PER_HAND] = {0};
         if (!transport_master(matrix + thisHand, slave_matrix)) {
-            error_count++;
-
-            if (error_count > ERROR_DISCONNECT_COUNT) {
+            if (!is_transport_connected()) {
                 // reset other half if disconnected
                 for (int i = 0; i < ROWS_PER_HAND; ++i) {
                     matrix[thatHand + i] = 0;
@@ -326,8 +318,6 @@ bool matrix_post_scan(void) {
                 changed = true;
             }
         } else {
-            error_count = 0;
-
             for (int i = 0; i < ROWS_PER_HAND; ++i) {
                 if (matrix[thatHand + i] != slave_matrix[i]) {
                     matrix[thatHand + i] = slave_matrix[i];

From 248b78ba6b5f832ff1fb57eaf658585bd942a326 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Wed, 4 Aug 2021 10:51:17 +0200
Subject: [PATCH 10/18] Move disconnection logic to `transport_master`.

Is a cleaner implementation, and causes the scan rate while disconnected
to increase instead of decrease.
---
 docs/feature_split_keyboard.md      |  6 ++---
 quantum/split_common/transactions.c | 37 +++++++++++++----------------
 quantum/split_common/transport.c    | 22 +++++++----------
 quantum/split_common/transport.h    |  4 ++--
 4 files changed, 30 insertions(+), 39 deletions(-)

diff --git a/docs/feature_split_keyboard.md b/docs/feature_split_keyboard.md
index 34fe29546eaf..620f29f0cee4 100644
--- a/docs/feature_split_keyboard.md
+++ b/docs/feature_split_keyboard.md
@@ -204,11 +204,9 @@ If you're having issues with serial communication, you can change this value, as
 This sets the maximum number of milliseconds before forcing a synchronization of data from master to slave. Under normal circumstances this sync occurs whenever the data _changes_, for safety a data transfer occurs after this number of milliseconds if no change has been detected since the last sync. 
 
 ```c
-#define SPLIT_MAX_CONNECTION_ERRORS 40
+#define SPLIT_MAX_CONNECTION_ERRORS 10
 ```
-This sets the maximum number of failed communication attempts from the master part before it assumes that no slave part is connected. This makes it possible to use a master part without the slave part connected.
-
-All built-in transactions (i.e. not `transaction_rpc_*`-based ones) are given 10 attempts each, and most send one transaction each over the transport, so 40 errors is basically (up to) four completely failed built-in transactions. On the other hand, each RPC transaction consists of four transport transactions without retries, so 40 errors is roughly ten completely failed RPC transactions. Setting it to a negative value will disable the disconnection check altogether.
+This sets the maximum number of failed communication attempts (one per scan cycle) from the master part before it assumes that no slave part is connected. This makes it possible to use a master part without the slave part connected.
 
 ```c
 #define SPLIT_CONNECTION_CHECK_TIMEOUT 500
diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index 0c9c906ed4e9..5d65465e8924 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -41,8 +41,8 @@
     { &dummy, 0, 0, sizeof_member(split_shared_memory_t, member), offsetof(split_shared_memory_t, member), cb }
 #define trans_target2initiator_initializer(member) trans_target2initiator_initializer_cb(member, NULL)
 
-#define transport_write(id, data, length) transport_transaction(id, data, length, NULL, 0)
-#define transport_read(id, data, length) transport_transaction(id, NULL, 0, data, length)
+#define transport_write(id, data, length) transport_execute_transaction(id, data, length, NULL, 0)
+#define transport_read(id, data, length) transport_execute_transaction(id, NULL, 0, data, length)
 
 #if defined(SPLIT_TRANSACTION_IDS_KB) || defined(SPLIT_TRANSACTION_IDS_USER)
 // Forward-declare the RPC callback handlers
@@ -53,29 +53,25 @@ void slave_rpc_exec_callback(uint8_t initiator2target_buffer_size, const void *i
 ////////////////////////////////////////////////////
 // Helpers
 
-bool transaction_handler_master(bool okay, matrix_row_t master_matrix[], matrix_row_t slave_matrix[], const char *prefix, bool (*handler)(matrix_row_t master_matrix[], matrix_row_t slave_matrix[])) {
-    if (okay) {
-        bool this_okay = true;
-        for (int iter = 1; iter <= 10; ++iter) {
-            if (!this_okay) {
-                for (int i = 0; i < iter * iter; ++i) {
-                    wait_us(10);
-                }
+bool transaction_handler_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[], const char *prefix, bool (*handler)(matrix_row_t master_matrix[], matrix_row_t slave_matrix[])) {
+    int num_retries = is_transport_connected() ? 10 : 1;
+    for (int iter = 1; iter <= num_retries; ++iter) {
+        if (iter > 1) {
+            for (int i = 0; i < iter * iter; ++i) {
+                wait_us(10);
             }
-            ATOMIC_BLOCK_FORCEON { this_okay = handler(master_matrix, slave_matrix); };
-            if (this_okay) break;
-        }
-        okay &= this_okay;
-        if (!okay) {
-            dprintf("Failed to execute %s\n", prefix);
         }
+        bool this_okay = true;
+        ATOMIC_BLOCK_FORCEON { this_okay = handler(master_matrix, slave_matrix); };
+        if (this_okay) return true;
     }
-    return okay;
+    dprintf("Failed to execute %s\n", prefix);
+    return false;
 }
 
 #define TRANSACTION_HANDLER_MASTER(prefix)                                                                \
     do {                                                                                                  \
-        okay &= transaction_handler_master(okay, master_matrix, slave_matrix, #prefix, &prefix##_master); \
+        if (!transaction_handler_master(master_matrix, slave_matrix, #prefix, &prefix##_master)) return false; \
     } while (0)
 
 #define TRANSACTION_HANDLER_SLAVE(prefix)                                      \
@@ -554,7 +550,6 @@ split_transaction_desc_t split_transaction_table[NUM_TOTAL_TRANSACTIONS] = {
 };
 
 bool transactions_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
-    bool okay = true;
     TRANSACTIONS_SLAVE_MATRIX_MASTER();
     TRANSACTIONS_MASTER_MATRIX_MASTER();
     TRANSACTIONS_ENCODERS_MASTER();
@@ -567,7 +562,7 @@ bool transactions_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix
     TRANSACTIONS_LED_MATRIX_MASTER();
     TRANSACTIONS_RGB_MATRIX_MASTER();
     TRANSACTIONS_WPM_MASTER();
-    return okay;
+    return true;
 }
 
 void transactions_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
@@ -598,6 +593,8 @@ void transaction_register_rpc(int8_t transaction_id, slave_callback_t callback)
 }
 
 bool transaction_rpc_exec(int8_t transaction_id, uint8_t initiator2target_buffer_size, const void *initiator2target_buffer, uint8_t target2initiator_buffer_size, void *target2initiator_buffer) {
+    // Prevent transaction attempts while transport is disconnected
+    if (!is_transport_connected()) { return false; }
     // Prevent invoking RPC on QMK core sync data
     if (transaction_id <= GET_RPC_RESP_DATA) return false;
     // Prevent sizing issues
diff --git a/quantum/split_common/transport.c b/quantum/split_common/transport.c
index 6c9da2797ebf..fe8ae676f427 100644
--- a/quantum/split_common/transport.c
+++ b/quantum/split_common/transport.c
@@ -22,12 +22,10 @@
 #include "transaction_id_define.h"
 #include "atomic_util.h"
 
-// Max number of consecutive failed communications before the communication is seen as disconnected.
-// All built-in transactions (i.e. not transaction_rpc_*-based ones) are given 10 attempts each, and most send one transaction over the transport, so 40 errors is basically (up to) four completely failed built-in transactions.
-// On the other hand, each RPC transaction consists of four transport transactions without retries, so 40 errors is roughly ten completely failed RPC transactions.
+// Max number of consecutive failed communications (one per scan cycle) before the communication is seen as disconnected.
 // Set to a negative value to disable the disconnection check altogether.
 #ifndef SPLIT_MAX_CONNECTION_ERRORS
-#    define SPLIT_MAX_CONNECTION_ERRORS 40
+#    define SPLIT_MAX_CONNECTION_ERRORS 10
 #endif  // SPLIT_MAX_CONNECTION_ERRORS
 
 // How long (in milliseconds) to block all connection attempts after the communication has been flagged as disconnected.
@@ -71,7 +69,7 @@ i2c_status_t transport_trigger_callback(int8_t id) {
     return i2c_writeReg(SLAVE_I2C_ADDRESS, trans->initiator2target_offset, split_trans_initiator2target_buffer(trans), trans->initiator2target_buffer_size, SLAVE_I2C_TIMEOUT);
 }
 
-static bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
+bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
     i2c_status_t              status;
     split_transaction_desc_t *trans = &split_transaction_table[id];
     if (initiator2target_length > 0) {
@@ -108,7 +106,7 @@ split_shared_memory_t *const split_shmem = &shared_memory;
 void transport_master_init(void) { soft_serial_initiator_init(); }
 void transport_slave_init(void) { soft_serial_target_init(); }
 
-static bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
+bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
     split_transaction_desc_t *trans = &split_transaction_table[id];
     if (initiator2target_length > 0) {
         size_t len = trans->initiator2target_buffer_size < initiator2target_length ? trans->initiator2target_buffer_size : initiator2target_length;
@@ -129,13 +127,11 @@ static bool transport_execute_transaction(int8_t id, const void *initiator2targe
 
 #endif  // USE_I2C
 
-bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { return transactions_master(master_matrix, slave_matrix); }
-
-void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { transactions_slave(master_matrix, slave_matrix); }
+bool is_transport_connected(void) { return connection_errors < SPLIT_MAX_CONNECTION_ERRORS; }
 
-bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length) {
+bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
 #if SPLIT_MAX_CONNECTION_ERRORS < 0
-    return transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length);
+    return transactions_master(master_matrix, slave_matrix);
 #else   // SPLIT_MAX_CONNECTION_ERRORS < 0
     // Throttle transaction attempts if target doesn't seem to be connected
     // Without this, a solo half becomes unusable due to constant read timeouts
@@ -144,7 +140,7 @@ bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t
         return false;
     }
 
-    if (!transport_execute_transaction(id, initiator2target_buf, initiator2target_length, target2initiator_buf, target2initiator_length)) {
+    if (!transactions_master(master_matrix, slave_matrix)) {
         if (connection_errors < UINT8_MAX) {
             connection_errors++;
         }
@@ -162,4 +158,4 @@ bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t
 #endif  // SPLIT_MAX_CONNECTION_ERRORS < 0
 }
 
-bool is_transport_connected(void) { return connection_errors < SPLIT_MAX_CONNECTION_ERRORS; }
+void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { transactions_slave(master_matrix, slave_matrix); }
diff --git a/quantum/split_common/transport.h b/quantum/split_common/transport.h
index 9d219874a029..674d9fac9666 100644
--- a/quantum/split_common/transport.h
+++ b/quantum/split_common/transport.h
@@ -38,7 +38,7 @@ void transport_slave_init(void);
 bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]);
 void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]);
 
-bool transport_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length);
+bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length);
 
 bool is_transport_connected(void);
 
@@ -174,4 +174,4 @@ typedef struct _split_shared_memory_t {
 #endif  // defined(SPLIT_TRANSACTION_IDS_KB) || defined(SPLIT_TRANSACTION_IDS_USER)
 } split_shared_memory_t;
 
-extern split_shared_memory_t *const split_shmem;
\ No newline at end of file
+extern split_shared_memory_t *const split_shmem;

From 5308e99e4df7e3f34f88fb84b7aea2284f6e4c52 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Wed, 4 Aug 2021 11:02:40 +0200
Subject: [PATCH 11/18] Lint fixes.

---
 quantum/split_common/transactions.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index 5d65465e8924..cde675be47ff 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -69,8 +69,8 @@ bool transaction_handler_master(matrix_row_t master_matrix[], matrix_row_t slave
     return false;
 }
 
-#define TRANSACTION_HANDLER_MASTER(prefix)                                                                \
-    do {                                                                                                  \
+#define TRANSACTION_HANDLER_MASTER(prefix)                                                                     \
+    do {                                                                                                       \
         if (!transaction_handler_master(master_matrix, slave_matrix, #prefix, &prefix##_master)) return false; \
     } while (0)
 
@@ -594,7 +594,9 @@ void transaction_register_rpc(int8_t transaction_id, slave_callback_t callback)
 
 bool transaction_rpc_exec(int8_t transaction_id, uint8_t initiator2target_buffer_size, const void *initiator2target_buffer, uint8_t target2initiator_buffer_size, void *target2initiator_buffer) {
     // Prevent transaction attempts while transport is disconnected
-    if (!is_transport_connected()) { return false; }
+    if (!is_transport_connected()) {
+        return false;
+    }
     // Prevent invoking RPC on QMK core sync data
     if (transaction_id <= GET_RPC_RESP_DATA) return false;
     // Prevent sizing issues

From 33e8e9fa8b0157e392635a3627316974bceab171 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Thu, 5 Aug 2021 12:49:55 +0200
Subject: [PATCH 12/18] Lower default `SERIAL_USART_TIMEOUT` to 20 ms.

The read timeout must be low enough to not cause exessively long scan
cycles when using a solo split half. 10 ms was determined from testing
to work fine even with the slowest defined baudrate of 19200 (5 ms was
too low for that case), so 20 ms should be fine for most cases.
---
 docs/serial_driver.md          | 6 +++---
 drivers/chibios/serial_usart.h | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/docs/serial_driver.md b/docs/serial_driver.md
index ed989b0a1519..3e89deffad9e 100644
--- a/docs/serial_driver.md
+++ b/docs/serial_driver.md
@@ -63,7 +63,7 @@ Configure the hardware via your config.h:
                                    //  5: about 19200 baud
 #define SERIAL_USART_DRIVER SD1    // USART driver of TX pin. default: SD1
 #define SERIAL_USART_TX_PAL_MODE 7 // Pin "alternate function", see the respective datasheet for the appropriate values for your MCU. default: 7
-#define SERIAL_USART_TIMEOUT 100 // USART driver timeout. default 100
+#define SERIAL_USART_TIMEOUT 20    // USART driver timeout. default 20
 ```
 
 You must also enable the ChibiOS `SERIAL` feature:
@@ -105,10 +105,10 @@ Next configure the hardware via your config.h:
                                    //  3: 57600 baud
                                    //  4: 38400 baud
                                    //  5: 19200 baud
-#define SERIAL_USART_DRIVER SD1 // USART driver of TX and RX pin. default: SD1
+#define SERIAL_USART_DRIVER SD1    // USART driver of TX and RX pin. default: SD1
 #define SERIAL_USART_TX_PAL_MODE 7 // Pin "alternate function", see the respective datasheet for the appropriate values for your MCU. default: 7
 #define SERIAL_USART_RX_PAL_MODE 7 // Pin "alternate function", see the respective datasheet for the appropriate values for your MCU. default: 7
-#define SERIAL_USART_TIMEOUT 100 // USART driver timeout. default 100
+#define SERIAL_USART_TIMEOUT 20    // USART driver timeout. default 20
 ```
 
 You must also enable the ChibiOS `SERIAL` feature:
diff --git a/drivers/chibios/serial_usart.h b/drivers/chibios/serial_usart.h
index c64e15566f19..7b135b31e055 100644
--- a/drivers/chibios/serial_usart.h
+++ b/drivers/chibios/serial_usart.h
@@ -110,7 +110,7 @@
 #endif
 
 #if !defined(SERIAL_USART_TIMEOUT)
-#    define SERIAL_USART_TIMEOUT 100
+#    define SERIAL_USART_TIMEOUT 20
 #endif
 
 #define HANDSHAKE_MAGIC 7

From b9c344120700000aefc0f6c042b23056e832cfae Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Thu, 5 Aug 2021 14:15:03 +0200
Subject: [PATCH 13/18] Remove `SERIAL_USART_TIMEOUT` from
 ergodox_infinity/config.h

Was somewhat mistakenly included in an earlier PR.
---
 keyboards/ergodox_infinity/config.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/keyboards/ergodox_infinity/config.h b/keyboards/ergodox_infinity/config.h
index e0208ba4d395..4bee8c3d931a 100644
--- a/keyboards/ergodox_infinity/config.h
+++ b/keyboards/ergodox_infinity/config.h
@@ -67,7 +67,6 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define SERIAL_USART_DRIVER SD1  // Only true for the master half
 #define SERIAL_USART_CONFIG { (SERIAL_USART_SPEED), } // Only field is speed
 #define SERIAL_USART_FULL_DUPLEX
-#define SERIAL_USART_TIMEOUT 50
 
 /* number of backlight levels */
 #define BACKLIGHT_LEVELS 3

From f725e8b8a63087858778018a8a74239461159243 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Thu, 5 Aug 2021 23:47:04 +0200
Subject: [PATCH 14/18] Fix building with `USE_I2C`.

---
 quantum/split_common/transport.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/quantum/split_common/transport.c b/quantum/split_common/transport.c
index fe8ae676f427..b755eefc906f 100644
--- a/quantum/split_common/transport.c
+++ b/quantum/split_common/transport.c
@@ -16,6 +16,7 @@
 
 #include <string.h>
 #include <debug.h>
+#include <timer.h>
 
 #include "transactions.h"
 #include "transport.h"

From a6f2ca558b5668c920454baf89c9887e68ce139f Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Fri, 6 Aug 2021 02:41:04 +0200
Subject: [PATCH 15/18] Reduce built firmware size.

Not really sure why this works, the idea was taken from tzarc's work on
split disconnection.
---
 quantum/split_common/transactions.c | 62 ++++++++++++++---------------
 1 file changed, 31 insertions(+), 31 deletions(-)

diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index cde675be47ff..4d2b86ff927e 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -53,7 +53,7 @@ void slave_rpc_exec_callback(uint8_t initiator2target_buffer_size, const void *i
 ////////////////////////////////////////////////////
 // Helpers
 
-bool transaction_handler_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[], const char *prefix, bool (*handler)(matrix_row_t master_matrix[], matrix_row_t slave_matrix[])) {
+static bool transaction_handler_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[], const char *prefix, bool (*handler)(matrix_row_t master_matrix[], matrix_row_t slave_matrix[])) {
     int num_retries = is_transport_connected() ? 10 : 1;
     for (int iter = 1; iter <= num_retries; ++iter) {
         if (iter > 1) {
@@ -69,14 +69,14 @@ bool transaction_handler_master(matrix_row_t master_matrix[], matrix_row_t slave
     return false;
 }
 
-#define TRANSACTION_HANDLER_MASTER(prefix)                                                                     \
-    do {                                                                                                       \
-        if (!transaction_handler_master(master_matrix, slave_matrix, #prefix, &prefix##_master)) return false; \
+#define TRANSACTION_HANDLER_MASTER(prefix)                                                                              \
+    do {                                                                                                                \
+        if (!transaction_handler_master(master_matrix, slave_matrix, #prefix, &prefix##_handlers_master)) return false; \
     } while (0)
 
-#define TRANSACTION_HANDLER_SLAVE(prefix)                                      \
-    do {                                                                       \
-        ATOMIC_BLOCK_FORCEON { prefix##_slave(master_matrix, slave_matrix); }; \
+#define TRANSACTION_HANDLER_SLAVE(prefix)                                               \
+    do {                                                                                \
+        ATOMIC_BLOCK_FORCEON { prefix##_handlers_slave(master_matrix, slave_matrix); }; \
     } while (0)
 
 inline static bool read_if_checksum_mismatch(int8_t trans_id_checksum, int8_t trans_id_retrieve, uint32_t *last_update, void *destination, const void *equiv_shmem, size_t length) {
@@ -134,8 +134,8 @@ static void slave_matrix_handlers_slave(matrix_row_t master_matrix[], matrix_row
 }
 
 // clang-format off
-#define TRANSACTIONS_SLAVE_MATRIX_MASTER() TRANSACTION_HANDLER_MASTER(slave_matrix_handlers)
-#define TRANSACTIONS_SLAVE_MATRIX_SLAVE() TRANSACTION_HANDLER_SLAVE(slave_matrix_handlers)
+#define TRANSACTIONS_SLAVE_MATRIX_MASTER() TRANSACTION_HANDLER_MASTER(slave_matrix)
+#define TRANSACTIONS_SLAVE_MATRIX_SLAVE() TRANSACTION_HANDLER_SLAVE(slave_matrix)
 #define TRANSACTIONS_SLAVE_MATRIX_REGISTRATIONS \
     [GET_SLAVE_MATRIX_CHECKSUM] = trans_target2initiator_initializer(smatrix.checksum), \
     [GET_SLAVE_MATRIX_DATA]     = trans_target2initiator_initializer(smatrix.matrix),
@@ -156,8 +156,8 @@ static void master_matrix_handlers_slave(matrix_row_t master_matrix[], matrix_ro
     memcpy(master_matrix, split_shmem->mmatrix.matrix, sizeof(split_shmem->mmatrix.matrix));
 }
 
-#    define TRANSACTIONS_MASTER_MATRIX_MASTER() TRANSACTION_HANDLER_MASTER(master_matrix_handlers)
-#    define TRANSACTIONS_MASTER_MATRIX_SLAVE() TRANSACTION_HANDLER_SLAVE(master_matrix_handlers)
+#    define TRANSACTIONS_MASTER_MATRIX_MASTER() TRANSACTION_HANDLER_MASTER(master_matrix)
+#    define TRANSACTIONS_MASTER_MATRIX_SLAVE() TRANSACTION_HANDLER_SLAVE(master_matrix)
 #    define TRANSACTIONS_MASTER_MATRIX_REGISTRATIONS [PUT_MASTER_MATRIX] = trans_initiator2target_initializer(mmatrix.matrix),
 
 #else  // SPLIT_TRANSPORT_MIRROR
@@ -192,8 +192,8 @@ static void encoder_handlers_slave(matrix_row_t master_matrix[], matrix_row_t sl
 }
 
 // clang-format off
-#    define TRANSACTIONS_ENCODERS_MASTER() TRANSACTION_HANDLER_MASTER(encoder_handlers)
-#    define TRANSACTIONS_ENCODERS_SLAVE() TRANSACTION_HANDLER_SLAVE(encoder_handlers)
+#    define TRANSACTIONS_ENCODERS_MASTER() TRANSACTION_HANDLER_MASTER(encoder)
+#    define TRANSACTIONS_ENCODERS_SLAVE() TRANSACTION_HANDLER_SLAVE(encoder)
 #    define TRANSACTIONS_ENCODERS_REGISTRATIONS \
     [GET_ENCODERS_CHECKSUM] = trans_target2initiator_initializer(encoders.checksum), \
     [GET_ENCODERS_DATA]     = trans_target2initiator_initializer(encoders.state),
@@ -234,8 +234,8 @@ static void sync_timer_handlers_slave(matrix_row_t master_matrix[], matrix_row_t
     }
 }
 
-#    define TRANSACTIONS_SYNC_TIMER_MASTER() TRANSACTION_HANDLER_MASTER(sync_timer_handlers)
-#    define TRANSACTIONS_SYNC_TIMER_SLAVE() TRANSACTION_HANDLER_SLAVE(sync_timer_handlers)
+#    define TRANSACTIONS_SYNC_TIMER_MASTER() TRANSACTION_HANDLER_MASTER(sync_timer)
+#    define TRANSACTIONS_SYNC_TIMER_SLAVE() TRANSACTION_HANDLER_SLAVE(sync_timer)
 #    define TRANSACTIONS_SYNC_TIMER_REGISTRATIONS [PUT_SYNC_TIMER] = trans_initiator2target_initializer(sync_timer),
 
 #else  // DISABLE_SYNC_TIMER
@@ -268,8 +268,8 @@ static void layer_state_handlers_slave(matrix_row_t master_matrix[], matrix_row_
 }
 
 // clang-format off
-#    define TRANSACTIONS_LAYER_STATE_MASTER() TRANSACTION_HANDLER_MASTER(layer_state_handlers)
-#    define TRANSACTIONS_LAYER_STATE_SLAVE() TRANSACTION_HANDLER_SLAVE(layer_state_handlers)
+#    define TRANSACTIONS_LAYER_STATE_MASTER() TRANSACTION_HANDLER_MASTER(layer_state)
+#    define TRANSACTIONS_LAYER_STATE_SLAVE() TRANSACTION_HANDLER_SLAVE(layer_state)
 #    define TRANSACTIONS_LAYER_STATE_REGISTRATIONS \
     [PUT_LAYER_STATE]         = trans_initiator2target_initializer(layers.layer_state), \
     [PUT_DEFAULT_LAYER_STATE] = trans_initiator2target_initializer(layers.default_layer_state),
@@ -299,8 +299,8 @@ static void led_state_handlers_slave(matrix_row_t master_matrix[], matrix_row_t
     set_split_host_keyboard_leds(split_shmem->led_state);
 }
 
-#    define TRANSACTIONS_LED_STATE_MASTER() TRANSACTION_HANDLER_MASTER(led_state_handlers)
-#    define TRANSACTIONS_LED_STATE_SLAVE() TRANSACTION_HANDLER_SLAVE(led_state_handlers)
+#    define TRANSACTIONS_LED_STATE_MASTER() TRANSACTION_HANDLER_MASTER(led_state)
+#    define TRANSACTIONS_LED_STATE_SLAVE() TRANSACTION_HANDLER_SLAVE(led_state)
 #    define TRANSACTIONS_LED_STATE_REGISTRATIONS [PUT_LED_STATE] = trans_initiator2target_initializer(led_state),
 
 #else  // SPLIT_LED_STATE_ENABLE
@@ -356,8 +356,8 @@ static void mods_handlers_slave(matrix_row_t master_matrix[], matrix_row_t slave
 #    endif
 }
 
-#    define TRANSACTIONS_MODS_MASTER() TRANSACTION_HANDLER_MASTER(mods_handlers)
-#    define TRANSACTIONS_MODS_SLAVE() TRANSACTION_HANDLER_SLAVE(mods_handlers)
+#    define TRANSACTIONS_MODS_MASTER() TRANSACTION_HANDLER_MASTER(mods)
+#    define TRANSACTIONS_MODS_SLAVE() TRANSACTION_HANDLER_SLAVE(mods)
 #    define TRANSACTIONS_MODS_REGISTRATIONS [PUT_MODS] = trans_initiator2target_initializer(mods),
 
 #else  // SPLIT_MODS_ENABLE
@@ -381,8 +381,8 @@ static bool backlight_handlers_master(matrix_row_t master_matrix[], matrix_row_t
 
 static void backlight_handlers_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { backlight_set(split_shmem->backlight_level); }
 
-#    define TRANSACTIONS_BACKLIGHT_MASTER() TRANSACTION_HANDLER_MASTER(backlight_handlers)
-#    define TRANSACTIONS_BACKLIGHT_SLAVE() TRANSACTION_HANDLER_SLAVE(backlight_handlers)
+#    define TRANSACTIONS_BACKLIGHT_MASTER() TRANSACTION_HANDLER_MASTER(backlight)
+#    define TRANSACTIONS_BACKLIGHT_SLAVE() TRANSACTION_HANDLER_SLAVE(backlight)
 #    define TRANSACTIONS_BACKLIGHT_REGISTRATIONS [PUT_BACKLIGHT] = trans_initiator2target_initializer(backlight_level),
 
 #else  // BACKLIGHT_ENABLE
@@ -418,8 +418,8 @@ static void rgblight_handlers_slave(matrix_row_t master_matrix[], matrix_row_t s
     }
 }
 
-#    define TRANSACTIONS_RGBLIGHT_MASTER() TRANSACTION_HANDLER_MASTER(rgblight_handlers)
-#    define TRANSACTIONS_RGBLIGHT_SLAVE() TRANSACTION_HANDLER_SLAVE(rgblight_handlers)
+#    define TRANSACTIONS_RGBLIGHT_MASTER() TRANSACTION_HANDLER_MASTER(rgblight)
+#    define TRANSACTIONS_RGBLIGHT_SLAVE() TRANSACTION_HANDLER_SLAVE(rgblight)
 #    define TRANSACTIONS_RGBLIGHT_REGISTRATIONS [PUT_RGBLIGHT] = trans_initiator2target_initializer(rgblight_sync),
 
 #else  // defined(RGBLIGHT_ENABLE) && defined(RGBLIGHT_SPLIT)
@@ -448,8 +448,8 @@ static void led_matrix_handlers_slave(matrix_row_t master_matrix[], matrix_row_t
     led_matrix_set_suspend_state(split_shmem->led_matrix_sync.led_suspend_state);
 }
 
-#    define TRANSACTIONS_LED_MATRIX_MASTER() TRANSACTION_HANDLER_MASTER(led_matrix_handlers)
-#    define TRANSACTIONS_LED_MATRIX_SLAVE() TRANSACTION_HANDLER_SLAVE(led_matrix_handlers)
+#    define TRANSACTIONS_LED_MATRIX_MASTER() TRANSACTION_HANDLER_MASTER(led_matrix)
+#    define TRANSACTIONS_LED_MATRIX_SLAVE() TRANSACTION_HANDLER_SLAVE(led_matrix)
 #    define TRANSACTIONS_LED_MATRIX_REGISTRATIONS [PUT_LED_MATRIX] = trans_initiator2target_initializer(led_matrix_sync),
 
 #else  // defined(LED_MATRIX_ENABLE) && defined(LED_MATRIX_SPLIT)
@@ -478,8 +478,8 @@ static void rgb_matrix_handlers_slave(matrix_row_t master_matrix[], matrix_row_t
     rgb_matrix_set_suspend_state(split_shmem->rgb_matrix_sync.rgb_suspend_state);
 }
 
-#    define TRANSACTIONS_RGB_MATRIX_MASTER() TRANSACTION_HANDLER_MASTER(rgb_matrix_handlers)
-#    define TRANSACTIONS_RGB_MATRIX_SLAVE() TRANSACTION_HANDLER_SLAVE(rgb_matrix_handlers)
+#    define TRANSACTIONS_RGB_MATRIX_MASTER() TRANSACTION_HANDLER_MASTER(rgb_matrix)
+#    define TRANSACTIONS_RGB_MATRIX_SLAVE() TRANSACTION_HANDLER_SLAVE(rgb_matrix)
 #    define TRANSACTIONS_RGB_MATRIX_REGISTRATIONS [PUT_RGB_MATRIX] = trans_initiator2target_initializer(rgb_matrix_sync),
 
 #else  // defined(RGB_MATRIX_ENABLE) && defined(RGB_MATRIX_SPLIT)
@@ -503,8 +503,8 @@ static bool wpm_handlers_master(matrix_row_t master_matrix[], matrix_row_t slave
 
 static void wpm_handlers_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { set_current_wpm(split_shmem->current_wpm); }
 
-#    define TRANSACTIONS_WPM_MASTER() TRANSACTION_HANDLER_MASTER(wpm_handlers)
-#    define TRANSACTIONS_WPM_SLAVE() TRANSACTION_HANDLER_SLAVE(wpm_handlers)
+#    define TRANSACTIONS_WPM_MASTER() TRANSACTION_HANDLER_MASTER(wpm)
+#    define TRANSACTIONS_WPM_SLAVE() TRANSACTION_HANDLER_SLAVE(wpm)
 #    define TRANSACTIONS_WPM_REGISTRATIONS [PUT_WPM] = trans_initiator2target_initializer(current_wpm),
 
 #else  // defined(WPM_ENABLE) && defined(SPLIT_WPM_ENABLE)

From 8ba50ea58b23c9be1df8437e3f04779f60245f08 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Fri, 6 Aug 2021 02:42:35 +0200
Subject: [PATCH 16/18] Tweak and improve opt-out for split disconnection
 logic.

There are now two ways to opt out from this feature:
* Set `SPLIT_MAX_CONNECTION_ERRORS` to 0. This will completely disable
  the connection status checks (also affects the slave matrix reset logic in
  matrix.c, though).
* Set `SPLIT_CONNECTION_CHECK_TIMEOUT` to 0. This will only disable the
  communication throttling while disconnected. Will make the firmware
  smaller.
---
 docs/feature_split_keyboard.md   |  4 ++++
 quantum/split_common/transport.c | 23 ++++++++++++++---------
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/docs/feature_split_keyboard.md b/docs/feature_split_keyboard.md
index 620f29f0cee4..27260b3fe2bb 100644
--- a/docs/feature_split_keyboard.md
+++ b/docs/feature_split_keyboard.md
@@ -208,6 +208,8 @@ This sets the maximum number of milliseconds before forcing a synchronization of
 ```
 This sets the maximum number of failed communication attempts (one per scan cycle) from the master part before it assumes that no slave part is connected. This makes it possible to use a master part without the slave part connected.
 
+Set to 0 to disable the disconnection check altogether.
+
 ```c
 #define SPLIT_CONNECTION_CHECK_TIMEOUT 500
 ```
@@ -215,6 +217,8 @@ How long (in milliseconds) the master part should block all connection attempts
 
 One communication attempt will be allowed everytime this amount of time has passed since the last attempt. If that attempt succeeds, the communication is seen as working again.
 
+Set to 0 to disable this throttling of communications while disconnected. This can save you a couple of bytes of firmware size.
+
 ```c
 #define SPLIT_TRANSPORT_MIRROR
 ```
diff --git a/quantum/split_common/transport.c b/quantum/split_common/transport.c
index b755eefc906f..9b9161fdfec2 100644
--- a/quantum/split_common/transport.c
+++ b/quantum/split_common/transport.c
@@ -24,13 +24,14 @@
 #include "atomic_util.h"
 
 // Max number of consecutive failed communications (one per scan cycle) before the communication is seen as disconnected.
-// Set to a negative value to disable the disconnection check altogether.
+// Set to 0 to disable the disconnection check altogether.
 #ifndef SPLIT_MAX_CONNECTION_ERRORS
 #    define SPLIT_MAX_CONNECTION_ERRORS 10
 #endif  // SPLIT_MAX_CONNECTION_ERRORS
 
 // How long (in milliseconds) to block all connection attempts after the communication has been flagged as disconnected.
 // One communication attempt will be allowed everytime this amount of time has passed since the last attempt. If that attempt succeeds, the communication is seen as working again.
+// Set to 0 to disable communication throttling while disconnected
 #ifndef SPLIT_CONNECTION_CHECK_TIMEOUT
 #    define SPLIT_CONNECTION_CHECK_TIMEOUT 500
 #endif  // SPLIT_CONNECTION_CHECK_TIMEOUT
@@ -131,32 +132,36 @@ bool transport_execute_transaction(int8_t id, const void *initiator2target_buf,
 bool is_transport_connected(void) { return connection_errors < SPLIT_MAX_CONNECTION_ERRORS; }
 
 bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
-#if SPLIT_MAX_CONNECTION_ERRORS < 0
-    return transactions_master(master_matrix, slave_matrix);
-#else   // SPLIT_MAX_CONNECTION_ERRORS < 0
+#if SPLIT_MAX_CONNECTION_ERRORS > 0 && SPLIT_CONNECTION_CHECK_TIMEOUT > 0
     // Throttle transaction attempts if target doesn't seem to be connected
     // Without this, a solo half becomes unusable due to constant read timeouts
     static uint16_t connection_check_timer = 0;
-    if (!is_transport_connected() && timer_elapsed(connection_check_timer) < SPLIT_CONNECTION_CHECK_TIMEOUT) {
+    const bool      is_disconnected        = !is_transport_connected();
+    if (is_disconnected && timer_elapsed(connection_check_timer) < SPLIT_CONNECTION_CHECK_TIMEOUT) {
         return false;
     }
+#endif  // SPLIT_MAX_CONNECTION_ERRORS > 0 && SPLIT_CONNECTION_CHECK_TIMEOUT > 0
 
-    if (!transactions_master(master_matrix, slave_matrix)) {
+    bool okay = transactions_master(master_matrix, slave_matrix);
+#if SPLIT_MAX_CONNECTION_ERRORS > 0
+    if (!okay) {
         if (connection_errors < UINT8_MAX) {
             connection_errors++;
         }
+#    if SPLIT_CONNECTION_CHECK_TIMEOUT > 0
         if (!is_transport_connected()) {
             connection_check_timer = timer_read();
             dprintln("Target disconnected, throttling connection attempts");
         }
         return false;
-    } else if (!is_transport_connected()) {
+    } else if (is_disconnected) {
         dprintln("Target connected");
+#    endif  // SPLIT_CONNECTION_CHECK_TIMEOUT > 0
     }
 
     connection_errors = 0;
-    return true;
-#endif  // SPLIT_MAX_CONNECTION_ERRORS < 0
+#endif  // SPLIT_MAX_CONNECTION_ERRORS > 0
+    return okay;
 }
 
 void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { transactions_slave(master_matrix, slave_matrix); }

From ff7062628e49628d2810310e8d88bd9cf973b720 Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Sat, 7 Aug 2021 13:39:54 +0200
Subject: [PATCH 17/18] Make split disconnection logic work with custom
 transports.

Includes a fallback implementation for keyboards using a custom
split_util.c but not a custom matrix.c (currently no such keyboard seems
to be merged, though).
---
 quantum/matrix.c                    | 26 ++++++++-------
 quantum/split_common/split_util.c   | 51 +++++++++++++++++++++++++++++
 quantum/split_common/split_util.h   |  5 +++
 quantum/split_common/transactions.c |  1 +
 quantum/split_common/transport.c    | 50 +---------------------------
 quantum/split_common/transport.h    |  2 --
 6 files changed, 73 insertions(+), 62 deletions(-)

diff --git a/quantum/matrix.c b/quantum/matrix.c
index 49784a987dc7..33586c431b38 100644
--- a/quantum/matrix.c
+++ b/quantum/matrix.c
@@ -303,27 +303,31 @@ void matrix_init(void) {
 }
 
 #ifdef SPLIT_KEYBOARD
+// Fallback implementation for keyboards not using the standard split_util.c
+__attribute__((weak)) bool transport_master_if_connected(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
+    transport_master(master_matrix, slave_matrix);
+    return true;  // Treat the transport as always connected
+}
+
 bool matrix_post_scan(void) {
     bool changed = false;
     if (is_keyboard_master()) {
         matrix_row_t slave_matrix[ROWS_PER_HAND] = {0};
-        if (!transport_master(matrix + thisHand, slave_matrix)) {
-            if (!is_transport_connected()) {
-                // reset other half if disconnected
-                for (int i = 0; i < ROWS_PER_HAND; ++i) {
-                    matrix[thatHand + i] = 0;
-                    slave_matrix[i]      = 0;
-                }
-
-                changed = true;
-            }
-        } else {
+        if (transport_master_if_connected(matrix + thisHand, slave_matrix)) {
             for (int i = 0; i < ROWS_PER_HAND; ++i) {
                 if (matrix[thatHand + i] != slave_matrix[i]) {
                     matrix[thatHand + i] = slave_matrix[i];
                     changed              = true;
                 }
             }
+        } else {
+            // reset other half if disconnected
+            for (int i = 0; i < ROWS_PER_HAND; ++i) {
+                matrix[thatHand + i] = 0;
+                slave_matrix[i]      = 0;
+            }
+
+            changed = true;
         }
 
         matrix_scan_quantum();
diff --git a/quantum/split_common/split_util.c b/quantum/split_common/split_util.c
index 8d414f6fe6b9..35f0a9d181dd 100644
--- a/quantum/split_common/split_util.c
+++ b/quantum/split_common/split_util.c
@@ -39,6 +39,21 @@
 #    define SPLIT_USB_TIMEOUT_POLL 10
 #endif
 
+// Max number of consecutive failed communications (one per scan cycle) before the communication is seen as disconnected.
+// Set to 0 to disable the disconnection check altogether.
+#ifndef SPLIT_MAX_CONNECTION_ERRORS
+#    define SPLIT_MAX_CONNECTION_ERRORS 10
+#endif  // SPLIT_MAX_CONNECTION_ERRORS
+
+// How long (in milliseconds) to block all connection attempts after the communication has been flagged as disconnected.
+// One communication attempt will be allowed everytime this amount of time has passed since the last attempt. If that attempt succeeds, the communication is seen as working again.
+// Set to 0 to disable communication throttling while disconnected
+#ifndef SPLIT_CONNECTION_CHECK_TIMEOUT
+#    define SPLIT_CONNECTION_CHECK_TIMEOUT 500
+#endif  // SPLIT_CONNECTION_CHECK_TIMEOUT
+
+static uint8_t connection_errors = 0;
+
 volatile bool isLeftHand = true;
 
 #if defined(SPLIT_USB_DETECT)
@@ -142,3 +157,39 @@ void split_post_init(void) {
         transport_slave_init();
     }
 }
+
+bool is_transport_connected(void) { return connection_errors < SPLIT_MAX_CONNECTION_ERRORS; }
+
+bool transport_master_if_connected(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
+#if SPLIT_MAX_CONNECTION_ERRORS > 0 && SPLIT_CONNECTION_CHECK_TIMEOUT > 0
+    // Throttle transaction attempts if target doesn't seem to be connected
+    // Without this, a solo half becomes unusable due to constant read timeouts
+    static uint16_t connection_check_timer = 0;
+    const bool      is_disconnected        = !is_transport_connected();
+    if (is_disconnected && timer_elapsed(connection_check_timer) < SPLIT_CONNECTION_CHECK_TIMEOUT) {
+        return false;
+    }
+#endif  // SPLIT_MAX_CONNECTION_ERRORS > 0 && SPLIT_CONNECTION_CHECK_TIMEOUT > 0
+
+    __attribute__((unused)) bool okay = transport_master(master_matrix, slave_matrix);
+#if SPLIT_MAX_CONNECTION_ERRORS > 0
+    if (!okay) {
+        if (connection_errors < UINT8_MAX) {
+            connection_errors++;
+        }
+#    if SPLIT_CONNECTION_CHECK_TIMEOUT > 0
+        bool connected = is_transport_connected();
+        if (!connected) {
+            connection_check_timer = timer_read();
+            dprintln("Target disconnected, throttling connection attempts");
+        }
+        return connected;
+    } else if (is_disconnected) {
+        dprintln("Target connected");
+#    endif  // SPLIT_CONNECTION_CHECK_TIMEOUT > 0
+    }
+
+    connection_errors = 0;
+#endif  // SPLIT_MAX_CONNECTION_ERRORS > 0
+    return true;
+}
diff --git a/quantum/split_common/split_util.h b/quantum/split_common/split_util.h
index a4c12519e056..ef72043bb786 100644
--- a/quantum/split_common/split_util.h
+++ b/quantum/split_common/split_util.h
@@ -5,8 +5,13 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+#include "matrix.h"
+
 extern volatile bool isLeftHand;
 
 void matrix_master_OLED_init(void);
 void split_pre_init(void);
 void split_post_init(void);
+
+bool transport_master_if_connected(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]);
+bool is_transport_connected(void);
diff --git a/quantum/split_common/transactions.c b/quantum/split_common/transactions.c
index 4d2b86ff927e..15f9b37ee722 100644
--- a/quantum/split_common/transactions.c
+++ b/quantum/split_common/transactions.c
@@ -23,6 +23,7 @@
 #include "quantum.h"
 #include "transactions.h"
 #include "transport.h"
+#include "split_util.h"
 #include "transaction_id_define.h"
 
 #define SYNC_TIMER_OFFSET 2
diff --git a/quantum/split_common/transport.c b/quantum/split_common/transport.c
index 9b9161fdfec2..3bbceae6dd55 100644
--- a/quantum/split_common/transport.c
+++ b/quantum/split_common/transport.c
@@ -23,21 +23,6 @@
 #include "transaction_id_define.h"
 #include "atomic_util.h"
 
-// Max number of consecutive failed communications (one per scan cycle) before the communication is seen as disconnected.
-// Set to 0 to disable the disconnection check altogether.
-#ifndef SPLIT_MAX_CONNECTION_ERRORS
-#    define SPLIT_MAX_CONNECTION_ERRORS 10
-#endif  // SPLIT_MAX_CONNECTION_ERRORS
-
-// How long (in milliseconds) to block all connection attempts after the communication has been flagged as disconnected.
-// One communication attempt will be allowed everytime this amount of time has passed since the last attempt. If that attempt succeeds, the communication is seen as working again.
-// Set to 0 to disable communication throttling while disconnected
-#ifndef SPLIT_CONNECTION_CHECK_TIMEOUT
-#    define SPLIT_CONNECTION_CHECK_TIMEOUT 500
-#endif  // SPLIT_CONNECTION_CHECK_TIMEOUT
-
-static uint8_t connection_errors = 0;
-
 #ifdef USE_I2C
 
 #    ifndef SLAVE_I2C_TIMEOUT
@@ -129,39 +114,6 @@ bool transport_execute_transaction(int8_t id, const void *initiator2target_buf,
 
 #endif  // USE_I2C
 
-bool is_transport_connected(void) { return connection_errors < SPLIT_MAX_CONNECTION_ERRORS; }
-
-bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) {
-#if SPLIT_MAX_CONNECTION_ERRORS > 0 && SPLIT_CONNECTION_CHECK_TIMEOUT > 0
-    // Throttle transaction attempts if target doesn't seem to be connected
-    // Without this, a solo half becomes unusable due to constant read timeouts
-    static uint16_t connection_check_timer = 0;
-    const bool      is_disconnected        = !is_transport_connected();
-    if (is_disconnected && timer_elapsed(connection_check_timer) < SPLIT_CONNECTION_CHECK_TIMEOUT) {
-        return false;
-    }
-#endif  // SPLIT_MAX_CONNECTION_ERRORS > 0 && SPLIT_CONNECTION_CHECK_TIMEOUT > 0
-
-    bool okay = transactions_master(master_matrix, slave_matrix);
-#if SPLIT_MAX_CONNECTION_ERRORS > 0
-    if (!okay) {
-        if (connection_errors < UINT8_MAX) {
-            connection_errors++;
-        }
-#    if SPLIT_CONNECTION_CHECK_TIMEOUT > 0
-        if (!is_transport_connected()) {
-            connection_check_timer = timer_read();
-            dprintln("Target disconnected, throttling connection attempts");
-        }
-        return false;
-    } else if (is_disconnected) {
-        dprintln("Target connected");
-#    endif  // SPLIT_CONNECTION_CHECK_TIMEOUT > 0
-    }
-
-    connection_errors = 0;
-#endif  // SPLIT_MAX_CONNECTION_ERRORS > 0
-    return okay;
-}
+bool transport_master(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { return transactions_master(master_matrix, slave_matrix); }
 
 void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]) { transactions_slave(master_matrix, slave_matrix); }
diff --git a/quantum/split_common/transport.h b/quantum/split_common/transport.h
index 674d9fac9666..c0de63e776f3 100644
--- a/quantum/split_common/transport.h
+++ b/quantum/split_common/transport.h
@@ -40,8 +40,6 @@ void transport_slave(matrix_row_t master_matrix[], matrix_row_t slave_matrix[]);
 
 bool transport_execute_transaction(int8_t id, const void *initiator2target_buf, uint16_t initiator2target_length, void *target2initiator_buf, uint16_t target2initiator_length);
 
-bool is_transport_connected(void);
-
 #ifdef ENCODER_ENABLE
 #    include "encoder.h"
 #    define NUMBER_OF_ENCODERS (sizeof((pin_t[])ENCODERS_PAD_A) / sizeof(pin_t))

From 0422030d7265729f2aae4286068bc89df19ac97d Mon Sep 17 00:00:00 2001
From: Joakim Tufvegren <jocke@barbanet.com>
Date: Fri, 20 Aug 2021 09:54:44 +0200
Subject: [PATCH 18/18] Remove unnecessary include of timer.h

Co-authored-by: Joel Challis <git@zvecr.com>
---
 quantum/split_common/transport.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/quantum/split_common/transport.c b/quantum/split_common/transport.c
index 3bbceae6dd55..bcc0261417d4 100644
--- a/quantum/split_common/transport.c
+++ b/quantum/split_common/transport.c
@@ -16,7 +16,6 @@
 
 #include <string.h>
 #include <debug.h>
-#include <timer.h>
 
 #include "transactions.h"
 #include "transport.h"