Use RTC1 for mills, micros, and delay (instead of SysTick)

cores/nRF5/delay.c

@@ -16,7 +16,7 @@
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
-#include "nrf.h"
+#include "nrf_rtc.h"
 
 #include "delay.h"
 #include "Arduino.h"
@@ -25,42 +25,20 @@
 extern "C" {
 #endif
 
-/** Tick Counter united by ms */
-static volatile uint32_t _ulTickCount=0 ;
+static volatile uint32_t overflows = 0;
 
 uint32_t millis( void )
 {
-// todo: ensure no interrupts
-  return _ulTickCount ;
+  uint64_t ticks = (uint64_t)(overflows << (uint64_t)32) | (uint64_t)nrf_rtc_counter_get(NRF_RTC1);
+
+  return (ticks * 1000) / RTC_INPUT_FREQ;
 }
 
-// Interrupt-compatible version of micros
-// Theory: repeatedly take readings of SysTick counter, millis counter and SysTick interrupt pending flag.
-// When it appears that millis counter and pending is stable and SysTick hasn't rolled over, use these
-// values to calculate micros. If there is a pending SysTick, add one to the millis counter in the calculation.
 uint32_t micros( void )
 {
-  uint32_t ticks, ticks2;
-  uint32_t pend, pend2;
-  uint32_t count, count2;
-
-  ticks2  = SysTick->VAL;
-  pend2   = !!(SCB->ICSR & SCB_ICSR_PENDSTSET_Msk)  ;
-  count2  = _ulTickCount ;
+  uint64_t ticks = (uint64_t)(overflows << (uint64_t)32) | (uint64_t)nrf_rtc_counter_get(NRF_RTC1);
 
-  do
-  {
-    ticks=ticks2;
-    pend=pend2;
-    count=count2;
-    ticks2  = SysTick->VAL;
-    pend2   = !!(SCB->ICSR & SCB_ICSR_PENDSTSET_Msk)  ;
-    count2  = _ulTickCount ;
-  } while ((pend != pend2) || (count != count2) || (ticks < ticks2));
-
-  return ((count+pend) * 1000) + (((SysTick->LOAD  - ticks)*(1048576/(VARIANT_MCK/1000000)))>>20) ;
-  // this is an optimization to turn a runtime division into two compile-time divisions and
-  // a runtime multiplication and shift, saving a few cycles
+  return (ticks * 1000000) / RTC_INPUT_FREQ;
 }
 
 void delay( uint32_t ms )
@@ -70,18 +48,19 @@ void delay( uint32_t ms )
     return ;
   }
 
-  uint32_t start = _ulTickCount ;
+  uint32_t start = millis() ;
 
   do
   {
     yield() ;
-  } while ( _ulTickCount - start < ms ) ;
+  } while ( millis() - start < ms ) ;
 }
 
-void SysTick_Handler(void)
+void RTC1_IRQHandler(void)
 {
-  // Increment tick count each ms
-  _ulTickCount++;
+  nrf_rtc_event_clear(NRF_RTC1, NRF_RTC_EVENT_OVERFLOW);
+
+  overflows = (overflows + 1) & 0xff;
 }
 
 #ifdef __cplusplus

cores/nRF5/nRF5_SDK_11/components/drivers_nrf/hal/nrf_rtc.h

@@ -29,7 +29,9 @@
 #include <stddef.h>
 #include <stdbool.h>
 #include "nrf.h"
+#ifndef ARDUINO
 #include "nrf_assert.h"
+#endif
 
 /**
  * @brief Macro for getting the number of compare channels available
@@ -268,7 +270,9 @@ __STATIC_INLINE uint32_t nrf_rtc_counter_get(NRF_RTC_Type * p_rtc)
 
 __STATIC_INLINE void nrf_rtc_prescaler_set(NRF_RTC_Type * p_rtc, uint32_t val)
 {
+#ifndef ARDUINO
     ASSERT(val <= (RTC_PRESCALER_PRESCALER_Msk >> RTC_PRESCALER_PRESCALER_Pos));
+#endif
     p_rtc->PRESCALER = val;
 }
 __STATIC_INLINE uint32_t rtc_prescaler_get(NRF_RTC_Type * p_rtc)

cores/nRF5/wiring.c

@@ -16,7 +16,8 @@
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
-#include "nrf.h"
+#include "nrf_clock.h"
+#include "nrf_rtc.h"
 
 #include "Arduino.h"
 
@@ -24,22 +25,19 @@
 extern "C" {
 #endif
 
-/*
- * Arduino Zero board initialization
- *
- * Good to know:
- *   - At reset, ResetHandler did the system clock configuration. Core is running at 48MHz.
- *   - Watchdog is disabled by default, unless someone plays with NVM User page
- *   - During reset, all PORT lines are configured as inputs with input buffers, output buffers and pull disabled.
- */
 void init( void )
 {
-  // Set Systick to 1ms interval, common to all Cortex-M variants
-  if ( SysTick_Config( SystemCoreClock / 1000 ) )
-  {
-    // Capture error
-    while ( 1 ) ;
-  }
+  NVIC_SetPriority(RTC1_IRQn, 15);
+  NVIC_ClearPendingIRQ(RTC1_IRQn);
+  NVIC_EnableIRQ(RTC1_IRQn);
+
+  nrf_clock_lf_src_set(CLOCK_LFCLKSRC_SRC_RC);
+  nrf_clock_task_trigger(NRF_CLOCK_TASK_LFCLKSTART);
+
+  nrf_rtc_prescaler_set(NRF_RTC1, 0);
+  nrf_rtc_event_enable(NRF_RTC1, NRF_RTC_EVENT_OVERFLOW);
+  nrf_rtc_int_enable(NRF_RTC1, NRF_RTC_EVENT_OVERFLOW);
+  nrf_rtc_task_trigger(NRF_RTC1, NRF_RTC_TASK_START);
 }
 
 #ifdef __cplusplus