HCI data length configuration option

README.md

@@ -15,12 +15,6 @@ https://github.com/stm32duino/wiki/wiki/STM32duinoBLE#stm32duinoble-with-x-nucle
 
 For more information about ArduinoBLE library please visit the official web page at:
 https://github.com/arduino-libraries/ArduinoBLE
-
-# Configuration
-STM32Cube_WPAN has several configuration options, which are set in the `app_conf.h`.
-This package has a default configuration named `app_conf_default.h`.
-The user can include the file `app_conf_custom.h` to customize the ble application. Options wrapped in `#ifndef, #endif` in `app_conf_default.h` can be overwritten. Additional options can be added.
-
 ## License
 
 ```
@@ -41,3 +35,12 @@ You should have received a copy of the GNU Lesser General Public
 License along with this library; if not, write to the Free Software
 Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 ```
+
+# Configuration
+STM32Cube_WPAN has several configuration options, which are set in the `app_conf.h`.
+This package has a default configuration named `app_conf_default.h`.
+The user can include the file `app_conf_custom.h` to customize the ble application. Options wrapped in `#ifndef, #endif` in `app_conf_default.h` can be overwritten. Additional options can be added.
+## HCI data length
+By default the data length (max payload per BLE packet) is set to 27 bytes. This can cause fragmentation when transmitting large characteristics using a large ATT_MTU.
+To increase the data length user must define `CFG_BLE_ENABLE_SET_DATA_LENGTH` (in `app_conf_default.h`). Further more, the wanted data length must bbe set in same define - eg: `#define CFG_BLE_ENABLE_SET_DATA_LENGTH 251`. Valid range: 27 --> 251.
+**Note: if this is enabled the pheripheral will attempt to increase the HCI data length with every connected device! There is no guarantee all BLE devices support all sizes!**

src/utility/ATT.cpp

@@ -256,6 +256,11 @@ void ATTClass::addConnection(uint16_t handle, uint8_t role, uint8_t peerBdaddrTy
   if (_eventHandlers[BLEConnected]) {
     _eventHandlers[BLEConnected](BLEDevice(peerBdaddrType, peerBdaddr));
   }
+  #ifdef CFG_BLE_ENABLE_SET_DATA_LENGTH
+  #if CFG_BLE_ENABLE_SET_DATA_LENGTH < 252 && CFG_BLE_ENABLE_SET_DATA_LENGTH > 26
+  HCI.hciSetDataLength(handle, CFG_BLE_ENABLE_SET_DATA_LENGTH, 2120);
+  #endif // CFG_BLE_ENABLE_SET_DATA_LENGTH < 252 && CFG_BLE_ENABLE_SET_DATA_LENGTH > 26
+  #endif // CFG_BLE_ENABLE_SET_DATA_LENGTH
 }
 
 void ATTClass::handleData(uint16_t connectionHandle, uint8_t dlen, uint8_t data[])

src/utility/HCI.cpp

@@ -672,6 +672,22 @@ void HCIClass::setTransport(HCITransportInterface *HCITransport)
   _HCITransport = HCITransport;
 }
 
+#ifdef CFG_BLE_ENABLE_SET_DATA_LENGTH
+int HCIClass::hciSetDataLength(uint16_t connectionHandle, uint16_t txOctects, uint16_t txTime){
+    const uint8_t payload_len = 6;
+    const uint16_t opcode = 0x2022;
+    uint8_t cmd_buffer[BLE_CMD_MAX_PARAM_LEN];
+    hci_le_set_data_length_cp0 *cp0 = (hci_le_set_data_length_cp0*)(cmd_buffer);
+
+    // create payload
+    cp0->Connection_Handle = connectionHandle;
+    cp0->TxOctets = txOctects;
+    cp0->TxTime = txTime;
+
+    return sendCommand(opcode, payload_len, cmd_buffer);
+}
+#endif // CFG_BLE_ENABLE_SET_DATA_LENGTH
+
 #if !defined(FAKE_HCI)
 HCIClass HCIObj;
 HCIClass& HCI = HCIObj;

src/utility/HCI.h

@@ -23,6 +23,18 @@
 #include <Arduino.h>
 #include "HCITransport.h"
 
+#if __has_include("app_conf_custom.h")
+#include "app_conf_custom.h"
+#endif
+
+#define BLE_CMD_MAX_PARAM_LEN 255
+
+struct hci_le_set_data_length_cp0{
+    uint16_t Connection_Handle;
+    uint16_t TxOctets;
+    uint16_t TxTime;
+};
+
 class HCIClass {
 public:
   HCIClass();
@@ -74,6 +86,23 @@ class HCIClass {
 
   void setTransport(HCITransportInterface *HCITransport);
 
+  #ifdef CFG_BLE_ENABLE_SET_DATA_LENGTH
+  //-----------------------------
+  // @brief 
+  // @param connectionHandle Connection_Handle Connection handle for which the command applies. 
+  //          Values: 0x0000 ... 0x0EFF
+  // @param txOctects TxOctets Preferred maximum number of payload octets that the local
+  //          Controller should include in a single Link Layer packet on this
+  //          connection.
+  //          Values: 0x001B ... 0x00FB
+  // @param txTime TxTime Preferred maximum number of microseconds that the local
+  //         Controller should use to transmit a single Link Layer packet on this
+  //         connection.
+  //         Values: 0x0148 ... 0x4290
+  // @return Value indicating success or error code.
+  int hciSetDataLength(uint16_t connectionHandle, uint16_t txOctects, uint16_t txTime);
+  #endif // CFG_BLE_ENABLE_SET_DATA_LENGTH
+
 private:
   virtual int sendCommand(uint16_t opcode, uint8_t plen = 0, void* parameters = NULL);