rtc: support periodic ticks at intervals from 1 to 128 Hz

watch-library/watch/watch_deepsleep.c

@@ -164,7 +164,7 @@ void watch_enter_shallow_sleep(char *message) {
     _watch_disable_all_peripherals_except_slcd();
 
     // disable tick interrupt
-    watch_disable_tick_callback();
+    watch_rtc_disable_all_tick_callbacks();
 
     // disable brownout detector interrupt, which could inadvertently wake us up.
     SUPC->INTENCLR.bit.BOD33DET = 1;
@@ -190,7 +190,7 @@ void watch_enter_deep_sleep() {
     // so let's do it!
     watch_register_extwake_callback(BTN_ALARM, NULL, true);
 
-    watch_disable_tick_callback();
+    watch_rtc_disable_all_tick_callbacks();
     _watch_disable_all_peripherals_except_slcd();
     slcd_sync_deinit(&SEGMENT_LCD_0);
     hri_mclk_clear_APBCMASK_SLCD_bit(SLCD);

watch-library/watch/watch_rtc.c

@@ -24,7 +24,7 @@
 
 #include "watch_rtc.h"
 
-ext_irq_cb_t tick_callback;
+ext_irq_cb_t tick_callbacks[8];
 ext_irq_cb_t alarm_callback;
 ext_irq_cb_t btn_alarm_callback;
 ext_irq_cb_t a2_callback;
@@ -70,15 +70,40 @@ watch_date_time watch_rtc_get_date_time() {
     return retval;
 }
 
-void watch_register_tick_callback(ext_irq_cb_t callback) {
+void watch_rtc_register_1Hz_callback(ext_irq_cb_t callback) {
-    tick_callback = callback;
+    watch_rtc_register_tick_callback(callback, 1);
-    NVIC_ClearPendingIRQ(RTC_IRQn);
-    NVIC_EnableIRQ(RTC_IRQn);
-    RTC->MODE2.INTENSET.reg = RTC_MODE2_INTENSET_PER7;
 }
 
-void watch_disable_tick_callback() {
+void watch_rtc_disable_1Hz_callback() {
-    RTC->MODE2.INTENCLR.reg = RTC_MODE2_INTENCLR_PER7;
+    watch_rtc_disable_tick_callback(1);
+}
+
+void watch_rtc_register_tick_callback(ext_irq_cb_t callback, uint8_t period) {
+    // we told them, it has to be a power of 2.
+    if (__builtin_popcount(period) != 1) return;
+
+    // this left-justifies the period in a 32-bit integer.
+    uint32_t tmp = period << 24;
+    // now we can count the leading zeroes to get the value we need.
+    // 0x01 (1 Hz) will have 7 leading zeros for PER7. 0xF0 (128 Hz) will have no leading zeroes for PER0.
+    uint8_t per_n = __builtin_clz(tmp);
+
+    // this also maps nicely to an index for our list of tick callbacks.
+    tick_callbacks[per_n] = callback;
+
+    NVIC_ClearPendingIRQ(RTC_IRQn);
+    NVIC_EnableIRQ(RTC_IRQn);
+    RTC->MODE2.INTENSET.reg = 1 << per_n;
+}
+
+void watch_rtc_disable_tick_callback(uint8_t period) {
+    if (__builtin_popcount(period) != 1) return;
+    uint8_t per_n = __builtin_clz(period << 24);
+    RTC->MODE2.INTENCLR.reg = 1 << per_n;
+}
+
+void watch_rtc_disable_all_tick_callbacks() {
+    RTC->MODE2.INTENCLR.reg = 0xFF;
 }
 
 void watch_rtc_register_alarm_callback(ext_irq_cb_t callback, watch_date_time alarm_time, watch_rtc_alarm_match mask) {
@@ -99,17 +124,20 @@ void RTC_Handler(void) {
     uint16_t interrupt_status = RTC->MODE2.INTFLAG.reg;
     uint16_t interrupt_enabled = RTC->MODE2.INTENSET.reg;
 
-    if ((interrupt_status & interrupt_enabled) & RTC_MODE2_INTFLAG_ALARM0) {
+    if ((interrupt_status & interrupt_enabled) & RTC_MODE2_INTFLAG_PER_Msk) {
-        if (alarm_callback != NULL) {
+        // handle the tick callback first, it's what we do the most.
-            alarm_callback();
+        // start from PER7, the 1 Hz tick.
+        for(int8_t i = 7; i >= 0; i--) {
+            if ((interrupt_status & interrupt_enabled) & (1 << i)) {
+                if (tick_callbacks[i] != NULL) {
+                    tick_callbacks[i]();
+                }
+                RTC->MODE2.INTFLAG.reg = 1 << i;
+                break;
+            }
         }
-        RTC->MODE2.INTFLAG.reg = RTC_MODE2_INTFLAG_ALARM0;
-    } else if ((interrupt_status & interrupt_enabled) & RTC_MODE2_INTFLAG_PER7) {
-        if (tick_callback != NULL) {
-            tick_callback();
-        }
-        RTC->MODE2.INTFLAG.reg = RTC_MODE2_INTFLAG_PER7;
     } else if ((interrupt_status & interrupt_enabled) & RTC_MODE2_INTFLAG_TAMPER) {
+        // handle the extwake interrupts next.
         uint8_t reason = RTC->MODE2.TAMPID.reg;
         if (reason & RTC_TAMPID_TAMPID2) {
             if (btn_alarm_callback != NULL) btn_alarm_callback();
@@ -120,6 +148,12 @@ void RTC_Handler(void) {
         }
         RTC->MODE2.TAMPID.reg = reason;
         RTC->MODE2.INTFLAG.reg = RTC_MODE2_INTFLAG_TAMPER;
+    } else if ((interrupt_status & interrupt_enabled) & RTC_MODE2_INTFLAG_ALARM0) {
+        // finally handle the alarm.
+        if (alarm_callback != NULL) {
+            alarm_callback();
+        }
+        RTC->MODE2.INTFLAG.reg = RTC_MODE2_INTFLAG_ALARM0;
     }
 }
 
@@ -152,3 +186,10 @@ void watch_get_date_time(struct calendar_date_time *date_time) {
     date_time->date.month = val.bit.MONTH;
     date_time->date.year = val.bit.YEAR + WATCH_RTC_REFERENCE_YEAR;
 }
+
+void watch_register_tick_callback(ext_irq_cb_t callback) {
+    tick_callbacks[7] = callback;
+    NVIC_ClearPendingIRQ(RTC_IRQn);
+    NVIC_EnableIRQ(RTC_IRQn);
+    RTC->MODE2.INTENSET.reg = RTC_MODE2_INTENSET_PER7;
+}

watch-library/watch/watch_rtc.h

@@ -106,11 +106,37 @@ void watch_rtc_disable_alarm_callback();
   * @param callback The function you wish to have called when the clock ticks. If you pass in NULL, the tick
   *                 interrupt will still be enabled, but no callback function will be called.
   */
-void watch_register_tick_callback(ext_irq_cb_t callback);
+void watch_rtc_register_1Hz_callback(ext_irq_cb_t callback);
 
-/** @brief Disables the tick callback.
+/** @brief Disables the tick callback for the given period.
   */
-void watch_disable_tick_callback();
+void watch_rtc_disable_1Hz_callback();
+
+/** @brief Registers a "tick" callback that will be called at a configurable period.
+  * @param callback The function you wish to have called when the clock ticks. If you pass in NULL, the tick
+  *                 interrupt will still be enabled, but no callback function will be called.
+  * @param period The frequency of the tick in Hz. **Must be a power of 2**, from 1 to 128 inclusive.
+  * @note A 1 Hz tick (@see watch_rtc_register_1Hz_callback) is suitable for most applications, in that it gives you a
+  *       chance to update the display once a second — an ideal update rate for a watch! If however you are displaying
+  *       a value (such as an accelerometer output) that updates more frequently than once per second, you may want to
+  *       tick at 16 or 32 Hz to update the screen more quickly. Just remember that the more frequent the tick, the more
+  *       power your app will consume. Ideally you should enable the fast tick only when the user requires it (i.e. in
+  *       response to an input event), and move back to the slow tick after some time.
+  *
+  *       Also note that the RTC peripheral does not have sub-second resolution, so even if you set a 2 or 4 Hz interval,
+  *       the system will not have any way of telling you where you are within a given second; watch_rtc_get_date_time
+  *       will return the exact same timestamp until the second ticks over.
+  */
+void watch_rtc_register_tick_callback(ext_irq_cb_t callback, uint8_t period);
+
+/** @brief Disables the tick callback for the given period.
+  * @param period The frequency of the tick you wish to disable, in Hz. **Must be a power of 2**, from 1 to 128.
+  */
+void watch_rtc_disable_tick_callback(uint8_t period);
+
+/** @brief Disables all tick callbacks.
+  */
+void watch_rtc_disable_all_tick_callbacks();
 
 /** @brief Sets the system date and time.
   * @param date_time A struct representing the date and time you wish to set.
@@ -124,5 +150,12 @@ void watch_set_date_time(struct calendar_date_time date_time);
 __attribute__((deprecated("Use the watch_rtc_get_date_time function instead")))
 void watch_get_date_time(struct calendar_date_time *date_time);
 
+/** @brief Registers a "tick" callback that will be called once per second.
+  * @param callback The function you wish to have called when the clock ticks. If you pass in NULL, the tick
+  *                 interrupt will still be enabled, but no callback function will be called.
+  */
+__attribute__((deprecated("Use the watch_rtc_register_1Hz_callback function instead")))
+void watch_register_tick_callback(ext_irq_cb_t callback);
+
 /// @}
 #endif