Merge pull request #2054 from ARMmbed/IOTTHD-3374

MAC: Use minimum CSMA for Asynch

Author: Jarkko Paso

source/MAC/IEEE802_15_4/mac_pd_sap.c

@@ -83,6 +83,10 @@ void mac_csma_backoff_start(protocol_interface_rf_mac_setup_s *rf_mac_setup)
 
 uint32_t mac_csma_backoff_get(protocol_interface_rf_mac_setup_s *rf_mac_setup)
 {
+    // Use minimum allowed CSMA-CA for asynch frames
+    if (rf_mac_setup->active_pd_data_request->asynch_request) {
+        return MIN_FHSS_CSMA_PERIOD_US;
+    }
     uint8_t backoff = mac_csma_random_backoff_get(rf_mac_setup);
     uint32_t backoff_in_us;
     //Multiple aUnitBackoffPeriod symbol time