Don't allow TX slot length go below allowed minimum (ARMmbed#2528)

Author: Jarkko Paso

source/Service_Libs/fhss/fhss_ws.c

@@ -195,7 +195,7 @@ void fhss_set_txrx_slot_length(fhss_structure_t *fhss_structure)
     if (fhss_structure->ws->fhss_configuration.fhss_broadcast_interval == 0 || fhss_structure->ws->fhss_configuration.fhss_bc_dwell_interval == 0) {
         return;
     }
-    uint32_t txrx_slot_length_ms_tmp = WS_TXRX_SLOT_LEN_MS;
+    uint32_t txrx_slot_length_ms_tmp = WS_TXRX_SLOT_LEN_MS_MAX;
     if (fhss_structure->callbacks.read_datarate) {
         /* Calculate minimum TX slot length which can fit optimal packet length twice.
          * Twice, because 0, 1, 4, 5... hop starts transmission at the beginning of TX slot and 2, 3, 6, 7... hop at the middle of TX slot
@@ -217,9 +217,14 @@ void fhss_set_txrx_slot_length(fhss_structure_t *fhss_structure)
         if (datarate) {
             txrx_slot_length_ms_tmp = ((fhss_structure->optimal_packet_length * 2) * (8000000 / datarate)) / 1000;
             // Do not allow using too high TX slot length.
-            if (txrx_slot_length_ms_tmp > WS_TXRX_SLOT_LEN_MS) {
-                tr_debug("TX slot length setting too high %"PRIu32"ms, using %"PRIu32"ms", txrx_slot_length_ms_tmp, (uint32_t)WS_TXRX_SLOT_LEN_MS);
-                txrx_slot_length_ms_tmp = WS_TXRX_SLOT_LEN_MS;
+            if (txrx_slot_length_ms_tmp > WS_TXRX_SLOT_LEN_MS_MAX) {
+                tr_debug("TX slot length setting too high %"PRIu32"ms, using %"PRIu32"ms", txrx_slot_length_ms_tmp, (uint32_t)WS_TXRX_SLOT_LEN_MS_MAX);
+                txrx_slot_length_ms_tmp = WS_TXRX_SLOT_LEN_MS_MAX;
+            }
+            // Do not allow using too low TX slot length.
+            if (txrx_slot_length_ms_tmp < WS_TXRX_SLOT_LEN_MS_MIN) {
+                tr_debug("TX slot length setting too low %"PRIu32"ms, using %"PRIu32"ms", txrx_slot_length_ms_tmp, (uint32_t)WS_TXRX_SLOT_LEN_MS_MIN);
+                txrx_slot_length_ms_tmp = WS_TXRX_SLOT_LEN_MS_MIN;
             }
         }
     }

source/Service_Libs/fhss/fhss_ws.h

@@ -19,8 +19,10 @@
 
 // TX slot length is optimised to this packet length
 #define OPTIMAL_PACKET_LENGTH   500
-// Default TX/RX slot length in milliseconds. Is used when datarate is not given by PHY.
-#define WS_TXRX_SLOT_LEN_MS             100
+// Max TX/RX slot length in milliseconds. Is used when datarate is not given by PHY or calculated slot length exceeds maximum allowed.
+#define WS_TXRX_SLOT_LEN_MS_MAX         100
+// Min TX/RX slot length in milliseconds. Is used when calculated slot length is under minimum allowed.
+#define WS_TXRX_SLOT_LEN_MS_MIN         10
 // Default minimum broadcast synchronization interval in seconds
 #define DEFAULT_MIN_SYNCH_INTERVAL      60
 // Drift compensation allowed if at least SYNCH_COMPENSATION_MIN_INTERVAL (seconds) since last synchronization