soc: arm: nordic nrf: use bitmode-16 for timing measurements in nrf51

nRF51 TIMER2 periperhal does not have the 32-bit
bitmode, so we need to fallback to the bitmode 16.

Signed-off-by: Ioannis Glaropoulos <[email protected]>

Author: ioannisg

soc/arm/nordic_nrf/timing.c

@@ -12,15 +12,18 @@
 
 #if defined(CONFIG_NRF_RTC_TIMER)
 
-
 #define CYCLES_PER_SEC (16000000 / (1 << NRF_TIMER2->PRESCALER))
 
 void timing_init(void)
 {
 	NRF_TIMER2->TASKS_CLEAR = 1; /* Clear Timer */
 	NRF_TIMER2->MODE = 0; /* Timer Mode */
 	NRF_TIMER2->PRESCALER = 0; /* 16M Hz */
+#if defined(CONFIG_SOC_SERIES_NRF51X)
+	NRF_TIMER2->BITMODE = 0; /* 16 - bit */
+#else
 	NRF_TIMER2->BITMODE = 3; /* 32 - bit */
+#endif
 }
 
 void timing_start(void)
@@ -42,7 +45,16 @@ timing_t timing_counter_get(void)
 uint64_t timing_cycles_get(volatile timing_t *const start,
 			   volatile timing_t *const end)
 {
+#if defined(CONFIG_SOC_SERIES_NRF51X)
+#define COUNTER_SPAN BIT(16)
+	if (*end >= *start) {
+		return (*end - *start);
+	} else {
+		return COUNTER_SPAN + *end - *start;
+	}
+#else
 	return (*end - *start);
+#endif
 }
 
 uint64_t timing_freq_get(void)