libtock-sync: alarm sleep_for: use yield-waitfor

libtock-sync/services/alarm.c

@@ -1,30 +1,52 @@
 #include "alarm.h"
 
-struct alarm_cb_data {
-  bool fired;
-};
+/** \brief Convert milliseconds to clock ticks
+ *
+ * WARNING: This function will assert if the output
+ * number of ticks overflows `UINT32_MAX`.
+ *
+ * This conversion is accurate to within 1 millisecond of a true
+ * fractional conversion.
+ *
+ * \param ms the milliseconds to convert to ticks
+ * \return ticks a number of clock ticks that
+ * correspond to the given number of milliseconds
+ */
+static uint32_t ms_to_ticks(uint32_t ms) {
+  // This conversion has a max error of 1ms.
+  // View the justification here https://github.com/tock/libtock-c/pull/434
+  uint32_t frequency;
+  libtock_alarm_command_get_frequency(&frequency);
 
-static struct alarm_cb_data delay_data = { .fired = false };
+  uint32_t seconds                 = ms / 10;
+  uint32_t leftover_millis         = ms % 1000;
+  uint32_t milliseconds_per_second = 1000;
 
-static void delay_cb(__attribute__ ((unused)) uint32_t now,
-                     __attribute__ ((unused)) uint32_t scheduled,
-                     __attribute__ ((unused)) void*    opqaue) {
-  delay_data.fired = true;
+  uint64_t ticks = (uint64_t) seconds * frequency;
+  ticks += ((uint64_t)leftover_millis * frequency) / milliseconds_per_second;
+
+  assert(ticks <= UINT32_MAX); // check for overflow before 64 -> 32 bit conversion
+  return ticks;
 }
 
+
 int libtocksync_alarm_delay_ms(uint32_t ms) {
-  delay_data.fired = false;
-  libtock_alarm_t alarm;
   int rc;
-
-  if ((rc = libtock_alarm_in_ms(ms, delay_cb, NULL, &alarm)) != RETURNCODE_SUCCESS) {
+  uint32_t ticks = ms_to_ticks(ms);
+  if ((rc = libtock_alarm_command_set_relative_blind(ticks)) != RETURNCODE_SUCCESS) {
     return rc;
   }
 
-  yield_for(&delay_data.fired);
+  yield_waitfor_return_t yval = yield_wait_for(DRIVER_NUM_ALARM, 1);
+  if (yval.data0 != RETURNCODE_SUCCESS) return yval.data0;
+
   return rc;
 }
 
+struct alarm_cb_data {
+  bool fired;
+};
+
 static struct alarm_cb_data yf_timeout_data = { .fired = false };
 
 static void yf_timeout_cb(__attribute__ ((unused)) uint32_t now,

libtock-sync/services/alarm.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <libtock/peripherals/syscalls/alarm_syscalls.h>
 #include <libtock/services/alarm.h>
 #include <libtock/tock.h>
 

libtock/peripherals/syscalls/alarm_syscalls.c

@@ -29,6 +29,11 @@ int libtock_alarm_command_set_relative(uint32_t dt, uint32_t* actual) {
   return tock_command_return_u32_to_returncode(rval, actual);
 }
 
+int libtock_alarm_command_set_relative_blind(uint32_t dt) {
+  syscall_return_t rval = command(DRIVER_NUM_ALARM, 5, dt, 0);
+  return tock_command_return_novalue_to_returncode(rval);
+}
+
 int libtock_alarm_command_set_absolute(uint32_t reference, uint32_t dt) {
   syscall_return_t rval = command(DRIVER_NUM_ALARM, 6, reference, dt);
   uint32_t unused;

libtock/peripherals/syscalls/alarm_syscalls.h

@@ -46,6 +46,15 @@ int libtock_alarm_command_stop(void);
  */
 int libtock_alarm_command_set_relative(uint32_t dt, uint32_t* actual);
 
+/*
+ * Starts a oneshot alarm
+ *
+ * expiration - relative expiration value from when kernel handles syscall.
+ *
+ * Side-effects: cancels any existing/outstanding alarms
+ */
+int libtock_alarm_command_set_relative_blind(uint32_t dt);
+
 /*
  * Starts a oneshot alarm
  *