Initial nRF51 analogWrite support via timer

cores/nRF5/wiring_analog_nRF51.c

@@ -18,6 +18,9 @@
 
 #ifdef NRF51
 
+#include "nrf_timer.h"
+#include "nrf_gpio.h"
+
 #include "Arduino.h"
 #include "wiring_private.h"
 
@@ -25,8 +28,27 @@
 extern "C" {
 #endif
 
-static int readResolution = 10;
-static int writeResolution = 8;
+#define PWM_COUNT 3
+#define PIN_FREE 0xffffffff
+
+struct PWMContext {
+  uint32_t pin;
+  uint32_t value;
+  nrf_timer_cc_channel_t channel;
+  nrf_timer_int_mask_t mask;
+  nrf_timer_event_t event;
+};
+
+static struct PWMContext pwmContext[PWM_COUNT] = {
+  { PIN_FREE, 0, NRF_TIMER_CC_CHANNEL1, NRF_TIMER_INT_COMPARE1_MASK, NRF_TIMER_EVENT_COMPARE1 },
+  { PIN_FREE, 0, NRF_TIMER_CC_CHANNEL2, NRF_TIMER_INT_COMPARE2_MASK, NRF_TIMER_EVENT_COMPARE2 },
+  { PIN_FREE, 0, NRF_TIMER_CC_CHANNEL3, NRF_TIMER_INT_COMPARE3_MASK, NRF_TIMER_EVENT_COMPARE3 }
+};
+
+static int timerEnabled = 0;
+
+static uint32_t readResolution = 10;
+static uint32_t writeResolution = 8;
 
 void analogReadResolution( int res )
 {
@@ -63,7 +85,6 @@ static inline uint32_t mapResolution( uint32_t value, uint32_t from, uint32_t to
  */
 void analogReference( eAnalogReference ulMode )
 {
-  return 0;
 }
 
 // Right now, PWM output only works on the pins with
@@ -72,7 +93,67 @@ void analogReference( eAnalogReference ulMode )
 // to digital output.
 void analogWrite( uint32_t ulPin, uint32_t ulValue )
 {
+  if (ulPin >= PINS_COUNT) {
+    return;
+  }
+
+  ulPin = g_ADigitalPinMap[ulPin];
+
+  if (!timerEnabled) {
+    NVIC_SetPriority(TIMER1_IRQn, 3);
+    NVIC_ClearPendingIRQ(TIMER1_IRQn);
+    NVIC_EnableIRQ(TIMER1_IRQn);
+
+    nrf_timer_mode_set(NRF_TIMER1, NRF_TIMER_MODE_TIMER);
+    nrf_timer_bit_width_set(NRF_TIMER1, NRF_TIMER_BIT_WIDTH_8);
+
+    nrf_timer_frequency_set(NRF_TIMER1, NRF_TIMER_FREQ_125kHz);
+    nrf_timer_cc_write(NRF_TIMER1, NRF_TIMER_CC_CHANNEL0, 0);
+    nrf_timer_int_enable(NRF_TIMER1, NRF_TIMER_INT_COMPARE0_MASK);
+
+    nrf_timer_task_trigger(NRF_TIMER1, NRF_TIMER_TASK_START);
+
+    timerEnabled = true;
+  }
 
+  for (int i = 0; i < PWM_COUNT; i++) {
+    if (pwmContext[i].pin == PIN_FREE || pwmContext[i].pin == ulPin) {
+      pwmContext[i].pin = ulPin;
+
+      nrf_gpio_cfg_output(ulPin);
+
+      ulValue = mapResolution(ulValue, writeResolution, 8);
+
+      pwmContext[i].value = ulValue;
+
+      nrf_timer_cc_write(NRF_TIMER1, pwmContext[i].channel, ulValue);
+      nrf_timer_int_enable(NRF_TIMER1, pwmContext[i].mask);
+      break;
+    }
+  }
+}
+
+void TIMER1_IRQHandler(void)
+{
+  if (nrf_timer_event_check(NRF_TIMER1, NRF_TIMER_EVENT_COMPARE0)) {
+    for (int i = 0; i < PWM_COUNT; i++) {
+      if (pwmContext[i].pin != PIN_FREE && pwmContext[i].value != 0) {
+        nrf_gpio_pin_write(pwmContext[i].pin, 1);
+      }
+    }
+
+    nrf_timer_event_clear(NRF_TIMER1, NRF_TIMER_EVENT_COMPARE0);
+  }
+
+  for (int i = 0; i < PWM_COUNT; i++) {
+    if (nrf_timer_event_check(NRF_TIMER1, pwmContext[i].event)) {
+      if (pwmContext[i].pin != PIN_FREE && pwmContext[i].value != 255) {
+        nrf_gpio_pin_write(pwmContext[i].pin, 0);
+      }
+
+      nrf_timer_event_clear(NRF_TIMER1, pwmContext[i].event);
+    }
+  }
 }
 
 #ifdef __cplusplus