refactor: try to read the temperature but smarter

examples/temperature.rs

@@ -1,10 +1,11 @@
+// NOTE: This is at least unreliable and likely wrong
+
 #![no_main]
 #![no_std]
 
-use defmt::info;
+use defmt::{debug, info};
-use hal::adc::{Adc, Ready, VTemp};
+use hal::adc::{Adc, Ready, VRef, VTemp};
-use hal::gpio::Analog;
+use hal::calibration::{VtempCal30, VtempCal130};
-use hal::gpio::gpiob::PB1;
 use panic_probe as _;
 
 use defmt_rtt as _; // global logger
@@ -12,8 +13,6 @@ use defmt_rtt as _; // global logger
 use cortex_m_rt::entry;
 use hal::{pac, prelude::*, rcc::Config};
 
-const MAGIC_TEMPERATURE_NUMBER: f32 = 12.412122;
-
 #[entry]
 fn main() -> ! {
     let dp = pac::Peripherals::take().unwrap();
@@ -22,28 +21,61 @@ fn main() -> ! {
     let mut rcc = dp.RCC.freeze(Config::hsi16());
     let mut adc = dp.ADC.constrain(&mut rcc);
 
-    let gpiob = dp.GPIOB.split(&mut rcc);
-
-    let mut temp_pin = gpiob.pb1.into_analog();
-
-    // Get the delay provider.
     let mut delay = cp.SYST.delay(rcc.clocks);
 
-    let mut temp;
+    // manual says i need to calibrate but then boom
-    let mut i = 0;
+    adc.set_sample_time(hal::adc::SampleTime::T_1_5);
+    delay.delay_ms(50_u16);
+    adc.calibrate().unwrap();
+    delay.delay_ms(5000_u16);
+
+    // NOTE: TSEN bit must be enabled for reading the temperature
+    VTemp.enable(&mut adc);
+
+    // reference temperatures from the chips readonly memory
+    // [Source](https://www.st.com/resource/en/datasheet/stm32l053r8.pdf),
+    // Table 6 in Secion 3.13 "Temperature sensor"
+    //
+    // More and better info in the large 1000+ page sheet "Ultra-low-power
+    // STM32L0x3 advanced Arm®-based 32-bit MCUs" (RM0367), 14.9
+    //
+    // This is basically calibration data
+    info!(
+        "reading calibration data... If this is the last thing you hear from me something has gone terribly wrong"
+    );
+    let vref_cal = hal::calibration::VrefintCal::get().read();
+    let tsense_cal1 = (30, VtempCal30::get().read());
+    let tsense_cal2 = (130, VtempCal130::get().read());
+    info!("tsense_cal1: {:?}", (30, tsense_cal1));
+    info!("tsense_cal2: {:?}", (130, tsense_cal2));
+
+    delay.delay_ms(50_u16);
+    let vref_actual: u16 = adc.read(&mut VRef).unwrap();
+    let vref_factor = vref_cal as f32 / vref_actual as f32;
+    debug!(
+        "vref real={} register={} => factor={}",
+        vref_actual, vref_cal, vref_factor
+    );
+
+    let mut temp_c;
+    let mut temp_mv;
     loop {
-        if i % 10_000 == 0 {
+        temp_mv = read_temp_mv(&mut adc, vref_factor);
-            temp = read_temp_c(&mut temp_pin, &mut adc);
+        temp_c = temp_mv_to_c(temp_mv, tsense_cal1, tsense_cal2);
-            info!("Temperature: {}", temp);
+        info!("Temperature: {:03}mv, {:04}c", temp_mv, temp_c as i32);
-        }
+        delay.delay_ms(500_u16);
-        // delay.delay_ms(200_u16);
-        i += 1;
     }
 }
 
-fn read_temp_c(pin: &mut PB1<Analog>, adc: &mut Adc<Ready>) -> i16 {
+fn read_temp_mv(adc: &mut Adc<Ready>, vref_factor: f32) -> f32 {
-    let v: f32 = adc
+    let bare: f32 = adc.read(&mut VTemp).expect("could not read with adc");
-        .read(pin /* or maybe VTemp from the adc module? */)
+    bare * vref_factor
-        .expect("could not read with adc");
+}
-    (v / MAGIC_TEMPERATURE_NUMBER) as i16 - 50
+
+// This unholy abomination is from the datasheet and does not actually look so bad if it's written
+// in Math instead of Rust.
+fn temp_mv_to_c(temp: f32, ts_cal_1: (i32, u16), ts_cal_2: (i32, u16)) -> f32 {
+    ((ts_cal_2.0 as f32 - ts_cal_1.0 as f32) / (ts_cal_2.1 as f32 - ts_cal_1.1 as f32))
+        * (temp - ts_cal_1.1 as f32)
+        + ts_cal_1.0 as f32
 }