Merge pull request #583 from rgrover/master

HAL: NRF51 - fix for the case where there are multiple tickers firing (issue #539)

Author: 0xc0170

libraries/mbed/common/us_ticker_api.c

@@ -37,7 +37,7 @@ void us_ticker_irq_handler(void) {
             return;
         }
 
-        if ((int)(head->timestamp - us_ticker_read()) <= 0) {
+        if ((int64_t)(head->timestamp - us_ticker_read()) <= 0) {
             // This event was in the past:
             //      point to the following one and execute its handler
             ticker_event_t *p = head;
@@ -70,7 +70,7 @@ void us_ticker_insert_event(ticker_event_t *obj, timestamp_t timestamp, uint32_t
     ticker_event_t *prev = NULL, *p = head;
     while (p != NULL) {
         /* check if we come before p */
-        if ((int)(timestamp - p->timestamp) <= 0) {
+        if ((int64_t)(timestamp - p->timestamp) < 0) {
             break;
         }
         /* go to the next element */

libraries/mbed/targets/hal/TARGET_NORDIC/TARGET_MCU_NRF51822/us_ticker.c

@@ -42,7 +42,7 @@ uint32_t us_ticker_read()
 
     timestamp_t value;
     app_timer_cnt_get(&value); /* This returns the RTC counter (which is fed by the 32khz crystal clock source) */
-    return (uint32_t)((value * 1000000) / APP_TIMER_CLOCK_FREQ); /* Return a pseudo microsecond counter value.
+    return ((value * 1000000) / (uint32_t)APP_TIMER_CLOCK_FREQ); /* Return a pseudo microsecond counter value.
                                                                   * This is only as precise as the 32khz low-freq
                                                                   * clock source, but could be adequate.*/
 }
@@ -78,15 +78,17 @@ void us_ticker_set_interrupt(timestamp_t timestamp)
     uint32_t targetCounter = ((uint32_t)((timestamp * (uint64_t)APP_TIMER_CLOCK_FREQ) / 1000000) + 1) & MAX_RTC_COUNTER_VAL;
     uint32_t ticksToCount = (targetCounter >= currentCounter) ?
                              (targetCounter - currentCounter) : (MAX_RTC_COUNTER_VAL + 1) - (currentCounter - targetCounter);
-    if (ticksToCount > 0) {
-        uint32_t rc;
-        rc = app_timer_start(us_ticker_appTimerID, ticksToCount, NULL /*p_context*/);
-        if (rc != NRF_SUCCESS) {
-            /* placeholder to do something to recover from error */
-            return;
-        }
-        us_ticker_appTimerRunning = true;
+    if (ticksToCount < APP_TIMER_MIN_TIMEOUT_TICKS) { /* Honour the minimum value of the timeout_ticks parameter of app_timer_start() */
+        ticksToCount = APP_TIMER_MIN_TIMEOUT_TICKS;
+    }
+
+    uint32_t rc;
+    rc = app_timer_start(us_ticker_appTimerID, ticksToCount, NULL /*p_context*/);
+    if (rc != NRF_SUCCESS) {
+        /* placeholder to do something to recover from error */
+        return;
     }
+    us_ticker_appTimerRunning = true;
 }
 
 void us_ticker_disable_interrupt(void)