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cpu/stm32/periph/timer: fix clobered IRQ flag

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The STM32 periph_timer driver reads the timer's status flags, then
clears them all. It is possible that a timer interrupt could occur
between reading the flag and clearing it. This would lead to a lost
interrupt.

The timer's status flags can be cleared by software, but can only be set
by the hardware. This patch takes advantage of this by only clearing the
flags it knows are set. The rest of the flags are set, which doesn't
actually change their state.
This commit is contained in:
Joshua DeWeese 2023-03-13 13:39:16 -04:00
parent 993e539651
commit dea25437c7
1 changed files with 6 additions and 1 deletions
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7
cpu/stm32/periph/timer.c
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@ -267,7 +267,12 @@ static inline void irq_handler(tim_t tim)
{
uint32_t top = dev(tim)->ARR;
uint32_t status = dev(tim)->SR & dev(tim)->DIER;
dev(tim)->SR = 0;
/* clear interrupts which we are about to service */
/* Note, the flags in the SR register can be cleared by software, but
* setting them has no effect on the register. Only the hardware can set
* them. */
dev(tim)->SR = ~status;
for (unsigned int i = 0; status; i++) {
uint32_t msk = TIM_SR_CC1IF << i;