Merge pull request ARMmbed#1700 from ARMmbed/IOTTHD-2483

FHSS: Calculate number of TX slots using defined slot length

Author: Jarkko Paso

source/Service_Libs/fhss/fhss_ws.c

@@ -317,11 +317,16 @@ static bool fhss_ws_check_tx_allowed(fhss_structure_t *fhss_structure)
     if (fhss_structure->ws->is_on_bc_channel == true) {
         return true;
     }
-    uint32_t slot_len_ms = (fhss_structure->ws->fhss_configuration.fhss_broadcast_interval - fhss_structure->ws->fhss_configuration.fhss_bc_dwell_interval) / (WS_NUMBER_OF_TX_SLOTS * 2);
+    uint8_t number_of_tx_slots = ((fhss_structure->ws->fhss_configuration.fhss_broadcast_interval - fhss_structure->ws->fhss_configuration.fhss_bc_dwell_interval) / WS_MAX_TXRX_SLOT_LEN_MS) / 2;
+    // Allow transmission when broadcast interval is very short comparing to MAX slot length
+    if (!number_of_tx_slots) {
+        return true;
+    }
+    uint32_t slot_len_ms = (fhss_structure->ws->fhss_configuration.fhss_broadcast_interval - fhss_structure->ws->fhss_configuration.fhss_bc_dwell_interval) / (number_of_tx_slots * 2);
     uint32_t remaining_time_ms = fhss_structure->platform_functions.fhss_get_remaining_slots(fhss_broadcast_handler, fhss_structure->fhss_api) / 1000;
     uint32_t tx_slot_begin = (fhss_structure->ws->fhss_configuration.fhss_broadcast_interval - fhss_structure->ws->fhss_configuration.fhss_bc_dwell_interval) - (slot_len_ms * (fhss_structure->own_hop & 1));
     uint32_t rx_slot_begin = tx_slot_begin - slot_len_ms;
-    uint8_t n_o_tx_slots = WS_NUMBER_OF_TX_SLOTS;
+    uint8_t n_o_tx_slots = number_of_tx_slots;
 
     while (n_o_tx_slots--) {
         if ((remaining_time_ms <= tx_slot_begin) && (remaining_time_ms > rx_slot_begin)) {

source/Service_Libs/fhss/fhss_ws.h

@@ -21,8 +21,8 @@
  * At least 4 channel retries must be used: (Initial channel + WS_NUMBER_OF_CHANNEL_RETRIES) * MAC attempts = (1+4)*4=20 attempts
  */
 #define WS_NUMBER_OF_CHANNEL_RETRIES    4
-//TODO: Make this configurable
-#define WS_NUMBER_OF_TX_SLOTS           2
+//TX/RX slot length in milliseconds
+#define WS_MAX_TXRX_SLOT_LEN_MS         100
 typedef struct fhss_ws fhss_ws_t;
 
 struct fhss_ws

test/nanostack/unittest/service_libs/fhss_ws/test_fhss_ws.c

@@ -327,12 +327,12 @@ bool test_fhss_ws_check_tx_conditions_callback()
     fhss_common_stub.fhss_struct.own_hop = 0;
     fhss_common_stub.fhss_struct.ws->fhss_configuration.fhss_broadcast_interval = 800;
     fhss_common_stub.fhss_struct.ws->fhss_configuration.fhss_bc_dwell_interval = 200;
-    fhss_platform_stub.remaining_slots_value = 500000;
+    fhss_platform_stub.remaining_slots_value = 550000;
     if (fhss_common_stub.fhss_struct.fhss_api->check_tx_conditions(api, DEFAULT_IS_BC_DEST, DEFAULT_HANDLE, DEFAULT_FRAME_TYPE, DEFAULT_FRAME_LENGTH, DEFAULT_PHY_HEAD_LENGTH, DEFAULT_PHY_TAIL_LENGTH) != true) {
         return false;
     }
     // Test TX not allowed for 0 hop
-    fhss_platform_stub.remaining_slots_value = 400000;
+    fhss_platform_stub.remaining_slots_value = 450000;
     if (fhss_common_stub.fhss_struct.fhss_api->check_tx_conditions(api, DEFAULT_IS_BC_DEST, DEFAULT_HANDLE, DEFAULT_FRAME_TYPE, DEFAULT_FRAME_LENGTH, DEFAULT_PHY_HEAD_LENGTH, DEFAULT_PHY_TAIL_LENGTH) != false) {
         return false;
     }
@@ -356,7 +356,7 @@ bool test_fhss_ws_check_tx_conditions_callback()
         return false;
     }
     // Test TX not allowed for 2nd hop
-    fhss_platform_stub.remaining_slots_value = 400000;
+    fhss_platform_stub.remaining_slots_value = 100000;
     if (fhss_common_stub.fhss_struct.fhss_api->check_tx_conditions(api, DEFAULT_IS_BC_DEST, DEFAULT_HANDLE, DEFAULT_FRAME_TYPE, DEFAULT_FRAME_LENGTH, DEFAULT_PHY_HEAD_LENGTH, DEFAULT_PHY_TAIL_LENGTH) != false) {
         return false;
     }