Use common us_ticker.c for NRF51 and NRF52 boards

Author: mprse

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/us_ticker.c

@@ -70,14 +70,18 @@ void us_ticker_init(void)
 
     /* Configure timer as follows:
      * - timer mode,
-     * - timer width 16 bits,
+     * - timer width 16 bits for NRF51 and 32 bits for NRF52,
      * - timer freq 1 MHz.
      */
     nrf_timer_mode_set(NRF_TIMER1, NRF_TIMER_MODE_TIMER);
 
     nrf_timer_frequency_set(NRF_TIMER1, NRF_TIMER_FREQ_1MHz);
 
+#ifdef NRF52
+    nrf_timer_bit_width_set(NRF_TIMER1, NRF_TIMER_BIT_WIDTH_32);
+#else
     nrf_timer_bit_width_set(NRF_TIMER1, NRF_TIMER_BIT_WIDTH_16);
+#endif
 
     nrf_timer_cc_write(NRF_TIMER1, NRF_TIMER_CC_CHANNEL0, 0);
 
@@ -110,7 +114,9 @@ void us_ticker_set_interrupt(timestamp_t timestamp)
 {
     core_util_critical_section_enter();
 
-    nrf_timer_cc_write(NRF_TIMER1, NRF_TIMER_CC_CHANNEL0, timestamp & 0xFFFF);
+    const uint32_t counter_mask = ((1 << US_TICKER_COUNTER_BITS) - 1);
+
+    nrf_timer_cc_write(NRF_TIMER1, NRF_TIMER_CC_CHANNEL0, timestamp & counter_mask);
 
     if (!nrf_timer_int_enable_check(NRF_TIMER1, nrf_timer_compare_int_get(NRF_TIMER_CC_CHANNEL0))) {
         nrf_timer_event_clear(NRF_TIMER1, NRF_TIMER_EVENT_COMPARE0);