Improve mp_hal_delay_ms by implementing subtick resolution.

Author: eightycc

supervisor/shared/tick.c

@@ -85,6 +85,13 @@ void supervisor_tick(void) {
     background_callback_add(&tick_callback, supervisor_background_tick, NULL);
 }
 
+uint64_t supervisor_get_raw_subticks(void) {
+    uint64_t ticks;
+    uint8_t subticks;
+    ticks = port_get_raw_ticks(&subticks);
+    return (ticks << 5) | subticks;
+}
+
 uint64_t supervisor_ticks_ms64() {
     uint64_t result;
     result = port_get_raw_ticks(NULL);
@@ -97,26 +104,29 @@ uint32_t supervisor_ticks_ms32() {
 }
 
 void mp_hal_delay_ms(mp_uint_t delay_ms) {
-    uint64_t start_tick = port_get_raw_ticks(NULL);
-    // Adjust the delay to ticks vs ms.
-    uint64_t delay_ticks = (delay_ms * (uint64_t)1024) / 1000;
-    uint64_t end_tick = start_tick + delay_ticks;
-    int64_t remaining = delay_ticks;
+    uint64_t start_subtick = supervisor_get_raw_subticks();
+    // Convert delay from ms to subticks
+    uint64_t delay_subticks = (delay_ms * (uint64_t)32768) / 1000;
+    uint64_t end_subtick = start_subtick + delay_subticks;
+    int64_t remaining = delay_subticks;
 
     // Loop until we've waited long enough or we've been CTRL-Ced by autoreload
     // or the user.
     while (remaining > 0 && !mp_hal_is_interrupted()) {
         RUN_BACKGROUND_TASKS;
-        remaining = end_tick - port_get_raw_ticks(NULL);
+        remaining = end_subtick - supervisor_get_raw_subticks();
         // We break a bit early so we don't risk setting the alarm before the time when we call
         // sleep.
         if (remaining < 1) {
             break;
         }
-        port_interrupt_after_ticks(remaining);
-        // Idle until an interrupt happens.
-        port_idle_until_interrupt();
-        remaining = end_tick - port_get_raw_ticks(NULL);
+        uint32_t remaining_ticks = remaining / 32;
+        if (remaining_ticks > 0) {
+            port_interrupt_after_ticks(remaining_ticks);
+            // Idle until an interrupt happens.
+            port_idle_until_interrupt();
+        }
+        remaining = end_subtick - supervisor_get_raw_subticks();
     }
 }
 

supervisor/shared/tick.h

@@ -33,6 +33,13 @@ extern uint32_t supervisor_ticks_ms32(void);
  */
 extern uint64_t supervisor_ticks_ms64(void);
 
+/** @brief Get 64-bit current time in subticks
+ *
+ * Time is returned as a 64-bit count of subticks where each subtick is 1/32768
+ * of a second.
+ */
+extern uint64_t supervisor_get_raw_subticks(void);
+
 extern void supervisor_enable_tick(void);
 extern void supervisor_disable_tick(void);