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sam d21: incorporate insights from Adafruit's Sleepydog library

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Joey Castillo 2025-06-14 16:18:15 -04:00
parent 1ff0cc58cf
commit 3b18ccb1f4
1 changed files with 14 additions and 0 deletions
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14
chips/samd21/system_samd21.c
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@ -211,6 +211,20 @@ bool set_cpu_frequency(uint32_t freq) {
}
void _enter_standby_mode() {
// Don't fully power down flash when in sleep
NVMCTRL->CTRLB.bit.SLEEPPRM = NVMCTRL_CTRLB_SLEEPPRM_DISABLED_Val;
// Set deep sleep mode
SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;
// Insight from Adafruit Sleepydog library: due to a hardware bug on the SAMD21,
// the SysTick interrupts become active before the flash has powered up from
// sleep, causing a hard fault. To prevent this the SysTick interrupts are disabled
// before entering sleep mode.
SysTick->CTRL &= ~SysTick_CTRL_TICKINT_Msk; // Disable SysTick interrupts
__DSB();
__WFI();
SysTick->CTRL |= SysTick_CTRL_TICKINT_Msk; // Enable SysTick interrupts
}