Finer grained, per port tick locking

Fixes #3504 hopefully.

Author: tannewt

ports/atmel-samd/common-hal/pulseio/PulseIn.h

@@ -51,7 +51,6 @@ void pulsein_reset(void);
 void pulsein_interrupt_handler(uint8_t channel);
 void pulsein_timer_interrupt_handler(uint8_t index);
 #ifdef SAMD21
-void rtc_set_continuous(void);
 void rtc_start_pulsein(void);
 void rtc_end_pulsein(void);
 #endif

ports/atmel-samd/supervisor/port.c

@@ -96,19 +96,21 @@
 #endif
 volatile bool hold_interrupt = false;
 #ifdef SAMD21
+static void rtc_set_continuous(bool continuous) {
+    while (RTC->MODE0.STATUS.bit.SYNCBUSY);
+    // TODO: DaveP: Do we need the RREQ here?
+    RTC->MODE0.READREQ.reg = RTC_READREQ_RREQ | (continuous ? RTC_READREQ_RCONT : 0) | 0x0010;
+    while (RTC->MODE0.STATUS.bit.SYNCBUSY);
+}
+
 void rtc_start_pulsein(void) {
-    rtc_set_continuous();
+    rtc_set_continuous(true);
     hold_interrupt = true;
 }
 
 void rtc_end_pulsein(void) {
     hold_interrupt = false;
-}
-
-void rtc_set_continuous(void) {
-    while (RTC->MODE0.STATUS.bit.SYNCBUSY);
-    RTC->MODE0.READREQ.reg = RTC_READREQ_RREQ | RTC_READREQ_RCONT | 0x0010;
-    while (RTC->MODE0.STATUS.bit.SYNCBUSY);
+    rtc_set_continuous(false);
 }
 #endif
 
@@ -430,19 +432,28 @@ uint32_t port_get_saved_word(void) {
 static volatile uint64_t overflowed_ticks = 0;
 static volatile bool _ticks_enabled = false;
 
-static uint32_t _get_count(void) {
+static uint32_t _get_count(uint32_t* overflow_count) {
     #ifdef SAM_D5X_E5X
     while ((RTC->MODE0.SYNCBUSY.reg & (RTC_MODE0_SYNCBUSY_COUNTSYNC | RTC_MODE0_SYNCBUSY_COUNT)) != 0) {}
     #endif
     #ifdef SAMD21
+    // Request a read so we don't stall the bus later. See section 14.3.1.5 Read Request
+    RTC->MODE0.READREQ.reg = RTC_READREQ_RREQ | 0x0010;
     while (RTC->MODE0.STATUS.bit.SYNCBUSY != 0) {}
     #endif
+    // Disable interrupts so we can grab the count and the overflow.
+    common_hal_mcu_disable_interrupts();
+    uint32_t count = RTC->MODE0.COUNT.reg;
+    if (overflow_count != NULL) {
+        *overflow_count = overflowed_ticks;
+    }
+    common_hal_mcu_enable_interrupts();
 
-    return RTC->MODE0.COUNT.reg;
+    return count;
 }
 
 static void _port_interrupt_after_ticks(uint32_t ticks) {
-    uint32_t current_ticks = _get_count();
+    uint32_t current_ticks = _get_count(NULL);
     if (ticks > 1 << 28) {
         // We'll interrupt sooner with an overflow.
         return;
@@ -490,12 +501,13 @@ void RTC_Handler(void) {
 }
 
 uint64_t port_get_raw_ticks(uint8_t* subticks) {
-    uint32_t current_ticks = _get_count();
+    uint32_t overflow_count;
+    uint32_t current_ticks = _get_count(&overflow_count);
     if (subticks != NULL) {
         *subticks = (current_ticks % 16) * 2;
     }
 
-    return overflowed_ticks + current_ticks / 16;
+    return overflow_count + current_ticks / 16;
 }
 
 // Enable 1/1024 second tick.
@@ -505,6 +517,7 @@ void port_enable_tick(void) {
     RTC->MODE0.INTENSET.reg = RTC_MODE0_INTENSET_PER2;
     #endif
     #ifdef SAMD21
+    // TODO: Switch to using the PER *event* from the RTC to generate an interrupt via EVSYS.
     _ticks_enabled = true;
     _port_interrupt_after_ticks(1);
     #endif

ports/litex/supervisor/port.c

@@ -128,7 +128,11 @@ uint32_t port_get_saved_word(void) {
 }
 
 uint64_t port_get_raw_ticks(uint8_t* subticks) {
-    return raw_ticks;
+    // Reading 64 bits may take two loads, so turn of interrupts while we do it.
+    irq_setie(false);
+    uint64_t raw_tick_snapshot = raw_ticks;
+    irq_setie(true);
+    return raw_tick_snapshot;
 }
 
 // Enable 1/1024 second tick.

ports/nrf/supervisor/port.c

@@ -274,11 +274,15 @@ uint32_t port_get_saved_word(void) {
 }
 
 uint64_t port_get_raw_ticks(uint8_t* subticks) {
+    common_hal_mcu_disable_interrupts();
     uint32_t rtc = nrfx_rtc_counter_get(&rtc_instance);
+    uint32_t overflow_count = overflow_tracker.overflowed_ticks;
+    common_hal_mcu_enable_interrupts();
+
     if (subticks != NULL) {
         *subticks = (rtc % 32);
     }
-    return overflow_tracker.overflowed_ticks + rtc / 32;
+    return overflow_count + rtc / 32;
 }
 
 // Enable 1/1024 second tick.

supervisor/shared/tick.c

@@ -125,9 +125,7 @@ void supervisor_tick(void) {
 
 uint64_t supervisor_ticks_ms64() {
     uint64_t result;
-    common_hal_mcu_disable_interrupts();
     result = port_get_raw_ticks(NULL);
-    common_hal_mcu_enable_interrupts();
     result = result * 1000 / 1024;
     return result;
 }