Improve the VREF calibration routine #132

atse · 2024-09-16T18:17:38+08:00

atse commented

2024-09-16 18:17:38 +08:00

VREF was incorrectly calibrated on a new v2.2.2 board, which calibrates its zero current point to be 2.2V instead of 1.5V

This PR implements a fix to the calibration problem. The fix is similar to Kirdy and calibrates VREF consistently in constant time.
This can also prevent boot-looping.

Reference from Kirdy's calibration sequence at

		src/thermostat/thermostat.rs
		Lines 317 to 344 in a512614de5
	
				    pub fn calibrate_dac_value(&mut self) {

				        const DAC_BIT: u32 = 18;

				        const ADC_BIT: u32 = 12;

				        let target_voltage = self.max1968.adc_read(AdcReadTarget::VREF, 512);

				        let mut start_value = 1;

				        let mut best_error = ElectricPotential::new::<volt>(100.0);

				        for step in (DAC_BIT - ADC_BIT - 1..DAC_BIT).rev() {

				            let mut prev_value = start_value;

				            for value in (start_value..=ad5680::MAX_VALUE).step_by(1 << step) {

				                self.max1968.phy.dac.set(value).unwrap();

				                sys_timer::sleep(5);

				                let dac_feedback = self.max1968.adc_read(AdcReadTarget::DacVfb, 64);

				                let error = target_voltage - dac_feedback;

				                if error < ElectricPotential::new::<volt>(0.0) {

				                    break;

				                } else if error < best_error {

				                    best_error = error;

				                    start_value = prev_value;

				                    let vref = (value as f32 / ad5680::MAX_VALUE as f32) * self.max1968.dac_out_range;

				                    self.set_center_pt(vref);

				                }

				                prev_value = value;

				            }

				        }

				        self.tec_settings.vref = target_voltage;

				    }

.

VREF was incorrectly calibrated on a new v2.2.2 board, which calibrates its zero current point to be 2.2V instead of 1.5V This PR implements a fix to the calibration problem. The fix is similar to Kirdy and calibrates VREF consistently in constant time. This can also prevent boot-looping. Reference from Kirdy's calibration sequence at https://git.m-labs.hk/M-Labs/kirdy/src/commit/a512614de535a6fb934ab848a1adc7b714f52eae/src/thermostat/thermostat.rs#L317-L344.

atse added 1 commit 2024-09-16 18:17:38 +08:00

Improve the VREF calibration routine 1041d3ecbb

* Fix wrong calibration of VREF on startup. Caused new v2.2.2 boards to
wrongly calibrate the zero-point to ~2.2 V instead of 1.5 V.

* Fix bootloop on some boards.

* Adjust watchdog interval accordingly.

mwojcik reviewed 2024-09-16 19:18:57 +08:00

src/main.rs

						
				@ -59,3 +59,3 @@

				const HSE: MegaHertz = MegaHertz(8);

				#[cfg(not(feature = "semihosting"))]

				const WATCHDOG_INTERVAL: u32 = 1_000;

				const WATCHDOG_INTERVAL: u32 = 2_000;