MAC: Implemented double cca check

Author: Jarkko Paso

nanostack/platform/arm_hal_phy.h

@@ -29,6 +29,11 @@
 extern "C" {
 #endif
 
+/** PHY_LINK_CCA_PREPARE status definitions */
+#define PHY_TX_NOT_ALLOWED  -1      /**< TX not allowed. Do not continue to CCA process. */
+#define PHY_TX_ALLOWED      0       /**< TX allowed. Continue to CCA process. */
+#define PHY_RESTART_CSMA    1       /**< Restart CSMA-CA timer. CSMA-CA period must be calculated using given backoff time (PHY_EXTENSION_SET_CSMA_PARAMETERS) */
+
 /** Interface states */
 typedef enum {
     PHY_INTERFACE_RESET,            /**< Reset PHY driver and set to idle. */
@@ -45,7 +50,8 @@ typedef enum {
     PHY_LINK_TX_SUCCESS,        /**< MAC TX complete. MAC will a make decision to enter wait ACK or TX done state. */
     PHY_LINK_TX_FAIL,           /**< Link TX process fail. */
     PHY_LINK_CCA_FAIL,          /**< RF link CCA process fail. */
-    PHY_LINK_CCA_PREPARE,       /**< RX Tx timeout prepare operation like channel switch to Tx channel from Receive one If operation fail must return not zero*/
+    PHY_LINK_CCA_OK,            /**< RF link CCA process ok. */
+    PHY_LINK_CCA_PREPARE,       /**< Prepare for CCA after CSMA-CA: changes to CCA channel and gives permission to TX. See PHY_LINK_CCA_PREPARE status definitions for return values */
 } phy_link_tx_status_e;
 
 /** Extension types */

source/MAC/IEEE802_15_4/mac_mcps_sap.c

@@ -1828,6 +1828,13 @@ static int8_t mcps_pd_data_cca_trig(protocol_interface_rf_mac_setup_s *rf_ptr, m
             }
             cca_enabled = true;
         }
+        // Use double CCA check with FHSS for data packets only
+        if (rf_ptr->fhss_api && !rf_ptr->mac_ack_tx_active && !rf_ptr->active_pd_data_request->asynch_request) {
+            if ((buffer->tx_time - (MAC_CSMA_MULTI_CCA_INTERVAL * (MAC_NUMBER_OF_CSMA_PERIODS - 1))) > mac_mcps_sap_get_phy_timestamp(rf_ptr)) {
+                buffer->csma_periods_left = MAC_NUMBER_OF_CSMA_PERIODS;
+                buffer->tx_time -= (MAC_CSMA_MULTI_CCA_INTERVAL * (MAC_NUMBER_OF_CSMA_PERIODS - 1));
+            }
+        }
         mac_pd_sap_set_phy_tx_time(rf_ptr, buffer->tx_time, cca_enabled);
         if (mac_plme_cca_req(rf_ptr) != 0) {
             if (buffer->fcf_dsn.frametype == MAC_FRAME_ACK) {

source/MAC/IEEE802_15_4/mac_mcps_sap.h

@@ -57,6 +57,11 @@ typedef enum {
 #define MAC_SAP_TRIG_TX                 7
 #define MCPS_SAP_DATA_ACK_CNF_EVENT     8
 
+// With FHSS we need to check CCA twice on TX channel
+#define MAC_NUMBER_OF_CSMA_PERIODS      2
+// Interval between two CCA checks
+#define MAC_CSMA_MULTI_CCA_INTERVAL    1000
+
 /**
  * @brief struct mac_aux_security_header_t MAC auxiliarity security header structure
  * INTERNAL use only
@@ -126,6 +131,7 @@ typedef struct mac_pre_build_frame {
     uint8_t *mac_payload;
     uint8_t status;
     uint8_t asynch_channel;
+    uint8_t csma_periods_left;
     uint32_t tx_time;
     bool upper_layer_request;
     bool mac_allocated_payload_ptr: 1;

source/MAC/IEEE802_15_4/mac_pd_sap.c

@@ -101,6 +101,10 @@ uint32_t mac_csma_backoff_get(protocol_interface_rf_mac_setup_s *rf_mac_setup)
         if (backoff_in_us < MIN_FHSS_CSMA_PERIOD_US) {
             backoff_in_us += MIN_FHSS_CSMA_PERIOD_US;
         }
+        // Backoff must be long enough to make multiple CCA checks
+        if (backoff_in_us < (MAC_CSMA_MULTI_CCA_INTERVAL * (MAC_NUMBER_OF_CSMA_PERIODS - 1))) {
+            backoff_in_us += (MAC_CSMA_MULTI_CCA_INTERVAL * (MAC_NUMBER_OF_CSMA_PERIODS - 1));
+        }
     }
     return backoff_in_us;
 }
@@ -405,17 +409,17 @@ static int8_t mac_data_interface_tx_done_cb(protocol_interface_rf_mac_setup_s *r
     if (status == PHY_LINK_CCA_PREPARE) {
 
         if (rf_ptr->mac_ack_tx_active) {
-            return 0;
+            return PHY_TX_ALLOWED;
         }
 
         if (mac_data_asynch_channel_switch(rf_ptr, rf_ptr->active_pd_data_request)) {
-            return 0;
+            return PHY_TX_ALLOWED;
         }
 
         if (rf_ptr->fhss_api) {
             mac_pre_build_frame_t *active_buf = rf_ptr->active_pd_data_request;
             if (!active_buf) {
-                return -1;
+                return PHY_TX_NOT_ALLOWED;
             }
 
             // Change to destination channel and write synchronization info to Beacon frames here
@@ -426,16 +430,21 @@ static int8_t mac_data_interface_tx_done_cb(protocol_interface_rf_mac_setup_s *r
             // When FHSS TX handle returns -1, transmission of the packet is currently not allowed -> restart CCA timer
             if (tx_handle_retval == -1) {
                 mac_sap_cca_fail_cb(rf_ptr);
-                return -2;
+                return PHY_TX_NOT_ALLOWED;
             }
             // When FHSS TX handle returns -3, we are trying to transmit broadcast packet on unicast channel -> push back
             // to queue by using CCA fail event
             if (tx_handle_retval == -3) {
                 mac_tx_done_state_set(rf_ptr, MAC_CCA_FAIL);
-                return -3;
+                return PHY_TX_NOT_ALLOWED;
             } else if (tx_handle_retval == -2) {
                 mac_tx_done_state_set(rf_ptr, MAC_UNKNOWN_DESTINATION);
-                return -2;
+                return PHY_TX_NOT_ALLOWED;
+            }
+            if (--active_buf->csma_periods_left > 0) {
+                active_buf->tx_time += MAC_CSMA_MULTI_CCA_INTERVAL;
+                mac_pd_sap_set_phy_tx_time(rf_ptr, active_buf->tx_time, true);
+                return PHY_RESTART_CSMA;
             }
         }
 
@@ -497,6 +506,9 @@ static int8_t mac_data_interface_tx_done_cb(protocol_interface_rf_mac_setup_s *r
             mac_sap_cca_fail_cb(rf_ptr);
             break;
 
+        case PHY_LINK_CCA_OK:
+            break;
+
         case PHY_LINK_TX_FAIL:
             mac_sap_no_ack_cb(rf_ptr);
             break;