shared-bindings: introduce, use common_hal_time_monotonic_ns

.. which, on some ports, can return sub-millisecond precision thanks to
how SysTick works.

Author: jepler

ports/atmel-samd/tick.c

@@ -32,6 +32,7 @@
 #include "supervisor/filesystem.h"
 #include "shared-bindings/microcontroller/__init__.h"
 #include "shared-bindings/microcontroller/Processor.h"
+#include "shared-bindings/time/__init__.h"
 
 #if CIRCUITPY_GAMEPAD
 #include "shared-module/gamepad/__init__.h"
@@ -131,3 +132,29 @@ void wait_until(uint64_t ms, uint32_t us_until_ms) {
     uint32_t ticks_per_us = common_hal_mcu_processor_get_frequency() / 1000 / 1000;
     while (ticks_ms <= ms && SysTick->VAL / ticks_per_us >= us_until_ms) {}
 }
+
+#if CIRCUITPY_FULL_BUILD
+uint64_t common_hal_time_monotonic_ns(void) {
+    uint32_t ticks_per_us = common_hal_mcu_processor_get_frequency() / 1000 / 1000;
+
+    // We disable interrupts to prevent ticks_ms from changing while we grab it.
+    common_hal_mcu_disable_interrupts();
+    uint32_t tick_status = SysTick->CTRL;
+    uint32_t current_us = SysTick->VAL;
+    uint32_t tick_status2 = SysTick->CTRL;
+    uint64_t current_ms = ticks_ms;
+    // The second clause ensures our value actually rolled over. Its possible it hit zero between
+    // the VAL read and CTRL read.
+    if ((tick_status & SysTick_CTRL_COUNTFLAG_Msk) != 0 ||
+        ((tick_status2 & SysTick_CTRL_COUNTFLAG_Msk) != 0 && current_us > ticks_per_us)) {
+        current_ms++;
+    }
+    common_hal_mcu_enable_interrupts();
+    return (current_ms + 1) * 1000000
+        - current_us * 1000 / ticks_per_us;
+}
+#else
+uint64_t common_hal_time_monotonic_ns(void) {
+    return common_hal_time_monotonic() * 1000000;
+}
+#endif

ports/cxd56/tick.c

@@ -43,3 +43,7 @@ void board_timerhook(void)
     autoreload_tick();
 #endif
 }
+
+uint64_t common_hal_time_monotonic_ns(void) {
+    return ticks_ms * 1000000;
+}

ports/nrf/tick.c

@@ -102,3 +102,23 @@ void wait_until(uint64_t ms, uint32_t us_until_ms) {
     uint32_t ticks_per_us = common_hal_mcu_processor_get_frequency() / 1000 / 1000;
     while(ticks_ms <= ms && SysTick->VAL / ticks_per_us >= us_until_ms) {}
 }
+
+uint64_t common_hal_time_monotonic_ns(void) {
+    uint32_t ticks_per_us = common_hal_mcu_processor_get_frequency() / 1000 / 1000;
+
+    // We disable interrupts to prevent ticks_ms from changing while we grab it.
+    common_hal_mcu_disable_interrupts();
+    uint32_t tick_status = SysTick->CTRL;
+    uint32_t current_us = SysTick->VAL;
+    uint32_t tick_status2 = SysTick->CTRL;
+    uint64_t current_ms = ticks_ms;
+    // The second clause ensures our value actually rolled over. Its possible it hit zero between
+    // the VAL read and CTRL read.
+    if ((tick_status & SysTick_CTRL_COUNTFLAG_Msk) != 0 ||
+        ((tick_status2 & SysTick_CTRL_COUNTFLAG_Msk) != 0 && current_us > ticks_per_us)) {
+        current_ms++;
+    }
+    common_hal_mcu_enable_interrupts();
+    return (current_ms + 1) * 1000000
+        - current_us * 1000 / ticks_per_us;
+}

ports/stm32f4/tick.c

@@ -30,6 +30,7 @@
 #include "supervisor/filesystem.h"
 #include "shared-module/gamepad/__init__.h"
 #include "shared-bindings/microcontroller/Processor.h"
+#include "shared-bindings/time/__init__.h"
 
 #include "stm32f4xx.h"
 
@@ -93,3 +94,7 @@ void wait_until(uint64_t ms, uint32_t us_until_ms) {
     uint32_t ticks_per_us = SystemCoreClock / 1000 / 1000;
     while(ticks_ms <= ms && SysTick->VAL / ticks_per_us >= us_until_ms) {}
 }
+
+uint64_t common_hal_time_monotonic_ns(void) {
+    return common_hal_time_monotonic() * 1000000;
+}

shared-bindings/time/__init__.c

@@ -216,7 +216,7 @@ MP_DEFINE_CONST_FUN_OBJ_0(time_time_obj, time_time);
 //|   :rtype: int
 //|
 STATIC mp_obj_t time_monotonic_ns(void) {
-    uint64_t time64 = common_hal_time_monotonic() * 1000000llu;
+    uint64_t time64 = common_hal_time_monotonic_ns();
     return mp_obj_new_int_from_ll((long long) time64);
 }
 MP_DEFINE_CONST_FUN_OBJ_0(time_monotonic_ns_obj, time_monotonic_ns);

shared-bindings/time/__init__.h

@@ -36,6 +36,7 @@ extern mp_obj_t struct_time_from_tm(timeutils_struct_time_t *tm);
 extern void struct_time_to_tm(mp_obj_t t, timeutils_struct_time_t *tm);
 
 extern uint64_t common_hal_time_monotonic(void);
+extern uint64_t common_hal_time_monotonic_ns(void);
 extern void common_hal_time_delay_ms(uint32_t);
 
 #endif  // MICROPY_INCLUDED_SHARED_BINDINGS_TIME___INIT___H