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watch_adc: enable ADC when checking battery; let's get rid of this footgun once and for all

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This commit is contained in:
Joey Castillo
2025-05-21 08:51:39 -04:00
parent 07a085e90b
commit 310ad3d095
10 changed files with 10 additions and 17 deletions
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8
watch-library/hardware/watch/watch_adc.c
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@ -67,6 +67,11 @@ void _watch_set_analog_reference_voltage(uint8_t reference) {
uint16_t watch_get_vcc_voltage(void) {
// stash the previous reference so we can restore it when we're done.
uint8_t oldref = ADC->REFCTRL.bit.REFSEL;
// same with the previous state of the ADC
bool adc_was_disabled = !adc_is_enabled();
// enable the ADC if needed
if (adc_was_disabled) watch_enable_adc();
// if we weren't already using the internal reference voltage, select it now.
if (oldref != ADC_REFCTRL_REFSEL_INTREF_Val) _watch_set_analog_reference_voltage(ADC_REFCTRL_REFSEL_INTREF_Val);
@ -77,6 +82,9 @@ uint16_t watch_get_vcc_voltage(void) {
// restore the old reference, if needed.
if (oldref != ADC_REFCTRL_REFSEL_INTREF_Val) _watch_set_analog_reference_voltage(oldref);
// and restore the ADC to its previous state
if (adc_was_disabled) watch_disable_adc();
return (uint16_t)((raw_val * 1000) / (1024 * 1 << ADC->AVGCTRL.bit.SAMPLENUM));
}

2
watch-library/hardware/watch/watch_private.c
View File

@ -51,9 +51,7 @@ void _watch_init(void) {
while(!SUPC->STATUS.bit.VREGRDY); // wait for voltage regulator to become ready
// check the battery voltage...
watch_enable_adc();
uint16_t battery_voltage = watch_get_vcc_voltage();
watch_disable_adc();
// ...because we can enable the more efficient low power regulator if the system voltage is > 2.5V
// still, enable LPEFF only if the battery voltage is comfortably above this threshold.
if (battery_voltage >= 2700) {

3
watch-library/shared/watch/watch_adc.h
View File

@ -53,7 +53,8 @@ void watch_enable_analog_input(const uint16_t pin);
uint16_t watch_get_analog_pin_level(const uint16_t pin);
/** @brief Returns the voltage of the VCC supply in millivolts (i.e. 3000 mV == 3.0 V). If running on
* a coin cell, this will be the battery voltage.
* a coin cell, this will be the battery voltage. If the ADC is not running when this function
* is called, it enabled the ADC briefly, and returns it to the off state.
* @details Unlike other ADC functions, this function does not return a raw value from the ADC, but
* rather scales it to an actual number of millivolts. This is because the ADC doesn't let
* us measure VCC per se; it instead lets us measure VCC / 4, and we choose to measure it