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movement: add voltage monitor watch face

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This commit is contained in:
Joey Castillo
2021-11-06 23:52:00 -04:00
parent 88f41b12fc
commit 0f03257ee9
6 changed files with 163 additions and 0 deletions
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29
watch-library/watch/watch_adc.c
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@@ -138,6 +138,35 @@ void watch_set_analog_sampling_length(uint8_t cycles) {
_watch_sync_adc();
}
void watch_set_analog_reference_voltage(watch_adc_reference_voltage reference) {
ADC->CTRLA.bit.ENABLE = 0;
if (reference == ADC_REFERENCE_INTREF) SUPC->VREF.bit.VREFOE = 1;
else SUPC->VREF.bit.VREFOE = 0;
ADC->REFCTRL.bit.REFSEL = reference;
ADC->CTRLA.bit.ENABLE = 1;
_watch_sync_adc();
// throw away one measurement after reference change (the channel doesn't matter).
_watch_get_analog_value(ADC_INPUTCTRL_MUXPOS_SCALEDCOREVCC);
}
uint16_t watch_get_vcc_voltage() {
// stash the previous reference so we can restore it when we're done.
uint8_t oldref = ADC->REFCTRL.bit.REFSEL;
// if we weren't already using the internal reference voltage, select it now.
if (oldref != ADC_REFERENCE_INTREF) watch_set_analog_reference_voltage(ADC_REFERENCE_INTREF);
// get the data
uint32_t raw_val = _watch_get_analog_value(ADC_INPUTCTRL_MUXPOS_SCALEDIOVCC_Val);
// restore the old reference, if needed.
if (oldref != ADC_REFERENCE_INTREF) watch_set_analog_reference_voltage(oldref);
return (uint16_t)((raw_val * 1000) / (1024 * 1 << ADC->AVGCTRL.bit.SAMPLENUM));
}
inline void watch_disable_analog_input(const uint8_t pin) {
gpio_set_pin_function(pin, GPIO_PIN_FUNCTION_OFF);
}

47
watch-library/watch/watch_adc.h
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@@ -94,6 +94,53 @@ void watch_set_analog_num_samples(uint16_t samples);
**/
void watch_set_analog_sampling_length(uint8_t cycles);
typedef enum {
ADC_REFERENCE_INTREF = ADC_REFCTRL_REFSEL_INTREF_Val,
ADC_REFERENCE_VCC_DIV1POINT6 = ADC_REFCTRL_REFSEL_INTVCC0_Val,
ADC_REFERENCE_VCC_DIV2 = ADC_REFCTRL_REFSEL_INTVCC1_Val,
ADC_REFERENCE_VCC = ADC_REFCTRL_REFSEL_INTVCC2_Val,
} watch_adc_reference_voltage;
/** @brief Selects the reference voltage to use for analog readings. Default is ADC_REFERENCE_VCC.
* @param reference One of ADC_REFERENCE_VCC, ADC_REFERENCE_VCC_DIV1POINT6, ADC_REFERENCE_VCC_DIV2
* or ADC_REFERENCE_INTREF.
* @details In order to turn an analog voltage into a 16-bit integer, the ADC needs to compare the
* measured voltage to a reference point. For example, if you were powering the watch with
* VCC == 3.0V and you had two 10K resistors connected in series from 3V to GND, you could
* expect to get 3 volts when you measure the top of the voltage divider, 0 volts at the
* bottom, and 1.5 volts in the middle. If you read these values uising a reference voltage
* of ADC_REFERENCE_VCC, the top value would be about 65535, the bottom about 0, and the
* middle about 32768. However! If we used ADC_REFERENCE_VCC_DIV2 as our reference, we would
* expect to get 65535 both at the top and the middle, because the largest value the ADC can
* measure in this configutation is 1.5V (VCC / 2).
*
* By changing the reference voltage from ADC_REFERENCE_VCC to ADC_REFERENCE_VCC_DIV1POINT6
* or ADC_REFERENCE_VCC_DIV2, you can get more resolution when measuring small voltages (i.e.
* a phototransistor circuit in low light).
*
* There is also a special reference voltage called ADC_REFERENCE_INTREF. The SAM L22's
* Supply Controller provides a selectable voltage reference (by default, 1.024 V) that you
* can select as a reference voltage for ADC conversions. Unlike the three references we
* talked about in the last paragraph, this reference voltage does not depend on VCC, which
* makes it very useful for measuring the battery voltage (since you can't really compare
* VCC to itself). You can change the INTREF voltage to 2.048 or 4.096 V by poking at the
* supply controller's VREF register, but the watch library does not support this use case.
**/
void watch_set_analog_reference_voltage(watch_adc_reference_voltage reference);
/** @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.
* @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
* against the internal reference voltage of 1.024 V. In short, the ADC gives us a number
* that's complicated to deal with, so we just turn it into a useful number for you :)
* @note This function depends on INTREF being 1.024V. If you have changed it by poking at the supply
* controller's VREF.SEL bits, this function will return inaccurate values.
*/
uint16_t watch_get_vcc_voltage();
/** @brief Disables the analog circuitry on the selected pin.
* @param pin One of pins A0-A4.
*/