channels: fix dac calibration

src/channels.rs

@@ -207,13 +207,37 @@ impl Channels {
         }
     }
 
-    /// for i_set
+    /// Calibrate the I_SET DAC using the DAC_FB ADC pin.
+    ///
+    /// These loops perform a width-first search for the DAC setting
+    /// that will produce a `target_voltage`.
     pub fn calibrate_dac_value(&mut self, channel: usize) {
-        let vref = self.read_vref(channel);
+        let target_voltage = Volts(2.5);
-        let value = self.calibrate_dac_value_for_voltage(channel, vref);
+        let mut start_value = 1;
-        info!("best dac value for {}: {}", vref, value);
+        let mut best_error = Volts(100.0);
 
-        let dac_factor = value as f64 / vref.0;
+        for step in (0..18).rev() {
+            let mut prev_value = start_value;
+            for value in (start_value..=ad5680::MAX_VALUE).step_by(1 << step) {
+                match channel {
+                    0 => {
+                        self.channel0.dac.set(value).unwrap();
+                    }
+                    1 => {
+                        self.channel1.dac.set(value).unwrap();
+                    }
+                    _ => unreachable!(),
+                }
+
+                let dac_feedback = self.read_dac_feedback_until_stable(channel, 0.001);
+                let error = target_voltage - dac_feedback;
+                if error < Volts(0.0) {
+                    break;
+                } else if error < best_error {
+                    best_error = error;
+                    start_value = prev_value;
+
+                    let dac_factor = value as f64 / dac_feedback.0;
                     match channel {
                         0 => self.channel0.dac_factor = dac_factor,
                         1 => self.channel1.dac_factor = dac_factor,
@@ -221,36 +245,11 @@ impl Channels {
                     }
                 }
 
-    fn calibrate_dac_value_for_voltage(&mut self, channel: usize, voltage: Volts) -> u32 {
+                prev_value = value;
-        let mut best_value = 0;
-        let mut best_error = Volts(100.0);
-
-        for step in (1..=12).rev() {
-            for value in (best_value..=ad5680::MAX_VALUE).step_by(2usize.pow(step)) {
-                match channel {
-                    0 => {
-                        self.channel0.dac.set(value).unwrap();
-                        // self.channel0.shdn.set_high().unwrap();
-                    }
-                    1 => {
-                        self.channel1.dac.set(value).unwrap();
-                        // self.channel1.shdn.set_high().unwrap();
-                    }
-                    _ => unreachable!(),
-                }
-
-                let dac_feedback = self.read_dac_feedback_until_stable(channel, 0.001);
-                let error = voltage - dac_feedback;
-                if error < Volts(0.0) {
-                    break;
-                } else if error < best_error {
-                    best_value = value;
-                    best_error = error;
-                }
             }
         }
 
+        // Reset
         self.set_dac(channel, Volts(0.0));
-        best_value
     }
 }

src/main.rs

@@ -97,7 +97,7 @@ fn main() -> ! {
     );
     let mut channels = Channels::new(pins);
     channels.calibrate_dac_value(0);
-
+    channels.calibrate_dac_value(1);
 
     #[cfg(not(feature = "generate-hwaddr"))]
     let hwaddr = EthernetAddress(NET_HWADDR);