FHSS WS: TX poll improvement to enhance hidden node situations

Author: Jarkko Paso

source/Service_Libs/fhss/fhss_ws.c

@@ -202,6 +202,18 @@ static int32_t fhss_ws_calc_bc_channel(fhss_structure_t *fhss_structure)
     return next_channel;
 }
 
+static uint8_t calc_own_tx_trig_slot(uint8_t own_hop)
+{
+    if (own_hop == 0xff) {
+        return 0;
+    }
+    if (own_hop & 1) {
+        own_hop--;
+    }
+    own_hop /= 2;
+    return (own_hop & 1);
+}
+
 static void fhss_broadcast_handler(const fhss_api_t *fhss_api, uint16_t delay)
 {
     int32_t next_channel;
@@ -236,13 +248,20 @@ static void fhss_broadcast_handler(const fhss_api_t *fhss_api, uint16_t delay)
         // Should return to own (unicast) listening channel after broadcast channel
         next_channel = fhss_structure->rx_channel;
         /* Start timer with random timeout to trigger unicast TX queue poll event.
-         * Min random is 1/30 of the TX slot length.
+         * For hops 0,1,4,5,8,9,...
+         * Min random is 1/100 of the TX slot length.
          * Max random is 1/10 of the TX slot length.
+         *
+         * For hops 2,3,6,7,10,11,...
+         * Min random is 1/100 of the TX slot length plus 0.5*TX slot length.
+         * Max random is 1/10 of the TX slot length plus 0.5*TX slot length.
          * Event timer resolution is 50us.
          */
+        // returns 1 if polling of TX queue is done on latter half of the TX slot
+        uint8_t own_tx_trig_slot = calc_own_tx_trig_slot(fhss_structure->own_hop);
         uint32_t txrx_slot_length_us = MS_TO_US(fhss_structure->ws->txrx_slot_length_ms);
-        uint16_t uc_min_random = (txrx_slot_length_us / 30) / 50;
-        uint16_t uc_max_random = (txrx_slot_length_us / 10) / 50;
+        uint16_t uc_min_random = (((txrx_slot_length_us / 2) * own_tx_trig_slot) / 50) + ((txrx_slot_length_us / 100) / 50);
+        uint16_t uc_max_random = (((txrx_slot_length_us / 2) * own_tx_trig_slot) / 50) + ((txrx_slot_length_us / 10) / 50);
         bool tx_allowed = fhss_ws_check_tx_allowed(fhss_structure);
         if (!tx_allowed) {
             uc_min_random += (txrx_slot_length_us) / 50;