jlaitine commented on code in PR #15929:
URL: https://github.com/apache/nuttx/pull/15929#discussion_r1983204204
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arch/risc-v/src/common/riscv_mtimer.c:
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@@ -211,19 +210,20 @@ static int riscv_mtimer_max_delay(struct
oneshot_lowerhalf_s *lower,
static int riscv_mtimer_start(struct oneshot_lowerhalf_s *lower,
oneshot_callback_t callback, void *arg,
- const struct timespec *ts)
+ clock_t ticks)
{
struct riscv_mtimer_lowerhalf_s *priv =
(struct riscv_mtimer_lowerhalf_s *)lower;
irqstate_t flags;
uint64_t mtime;
+ clock_t current;
uint64_t alarm;
flags = up_irq_save();
mtime = riscv_mtimer_get_mtime(priv);
- alarm = mtime + ts->tv_sec * priv->freq +
- ts->tv_nsec * priv->freq / NSEC_PER_SEC;
+ current = mtime * TICK_PER_SEC / priv->freq;
+ alarm = (current + ticks) * priv->freq / TICK_PER_SEC;
Review Comment:
No, this is exactly what can't be done. The first conversion calculates the
"current" tick. the (current + tick) calculates the tick on which the wakeup
needs to be set. The "(current + ticks) * priv->freq / TICK_PER_SEC" properly
aligns the compare register value on the proper boundary.
If you'd leave out the first conversion, you'd return the issue of timer
drift, as the "mtime" is not the accurate start time of the tick.
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