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arm64: Disable timer when not in use.

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* ARM documentation indicates this may save power.
* Notably, the timer keeps ticking even when "disabled", but
  cannot be read by the core without temporarily "enabling"
  the timer.

Change-Id: Iccff84915c611b43ee7a3c53ed2f8a3e426eda06
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8093
Haiku-Format: Haiku-format Bot <[email protected]>
Tested-by: Commit checker robot <[email protected]>
Reviewed-by: Adrien Destugues <[email protected]>
This commit is contained in:
Owen Anderson
2024-08-23 15:16:21 +00:00
committed by waddlesplash
parent 653d40cc93
commit b278b98232
1 changed files with 9 additions and 6 deletions
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src/system/kernel/arch/arm64/arch_timer.cpp
+9 -6
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@@ -16,8 +16,11 @@ static uint64 sTimerTicksUS;
static bigtime_t sTimerMaxInterval;
static uint64 sBootTime;
#define TIMER_ARMED (1)
#define TIMER_MASKED (2 | 1)
#define TIMER_DISABLED (0)
#define TIMER_ENABLE (1)
#define TIMER_IMASK (2)
#define TIMER_ISTATUS (4)
#define TIMER_IRQ 27
@@ -28,21 +31,21 @@ arch_timer_set_hardware_timer(bigtime_t timeout)
timeout = sTimerMaxInterval;
WRITE_SPECIALREG(CNTV_TVAL_EL0, timeout * sTimerTicksUS);
WRITE_SPECIALREG(CNTV_CTL_EL0, TIMER_ARMED);
WRITE_SPECIALREG(CNTV_CTL_EL0, TIMER_ENABLE);
}
void
arch_timer_clear_hardware_timer()
{
WRITE_SPECIALREG(CNTV_CTL_EL0, TIMER_MASKED);
WRITE_SPECIALREG(CNTV_CTL_EL0, TIMER_DISABLED);
}
int32
arch_timer_interrupt(void *data)
{
WRITE_SPECIALREG(CNTV_CTL_EL0, TIMER_MASKED);
WRITE_SPECIALREG(CNTV_CTL_EL0, TIMER_DISABLED);
return timer_interrupt();
}
@@ -53,7 +56,7 @@ arch_init_timer(kernel_args *args)
sTimerTicksUS = READ_SPECIALREG(CNTFRQ_EL0) / 1000000;
sTimerMaxInterval = INT32_MAX / sTimerTicksUS;
WRITE_SPECIALREG(CNTV_CTL_EL0, TIMER_MASKED);
WRITE_SPECIALREG(CNTV_CTL_EL0, TIMER_DISABLED);
install_io_interrupt_handler(TIMER_IRQ, &arch_timer_interrupt, NULL, 0);
sBootTime = READ_SPECIALREG(CNTPCT_EL0);