adc: read u32 for unipolar coding

src/ad7172/adc.rs

@@ -129,7 +129,7 @@ impl<SPI: Transfer<u8, Error = E>, NSS: OutputPin, E: fmt::Debug> Adc<SPI, NSS>
     }
 
     /// Get data
-    pub fn read_data(&mut self) -> Result<i32, AdcError<SPI::Error>> {
+    pub fn read_data(&mut self) -> Result<u32, AdcError<SPI::Error>> {
         self.read_reg(&regs::Data)
             .map(|data| data.data())
     }

src/ad7172/regs.rs

@@ -160,16 +160,10 @@ impl if_mode::Data {
 
 def_reg!(Data, data, 0x04, 3);
 impl data::Data {
-    pub fn data(&self) -> i32 {
-        let raw =
-            (u32::from(self.0[0]) << 16) |
-            (u32::from(self.0[1]) << 8) |
-            u32::from(self.0[2]);
-        if raw & 0x80_0000 != 0 {
-            ((raw & 0x7F_FFFF) | 0x8000_0000) as i32
-        } else {
-            raw as i32
-        }
+    pub fn data(&self) -> u32 {
+        (u32::from(self.0[0]) << 16) |
+        (u32::from(self.0[1]) << 8) |
+        u32::from(self.0[2])
     }
 }
 

src/channel_state.rs

@@ -3,7 +3,7 @@ use crate::{ad5680, ad7172, pid, steinhart_hart as sh};
 
 
 pub struct ChannelState {
-    pub adc_data: Option<i32>,
+    pub adc_data: Option<u32>,
     pub adc_time: Instant,
     pub dac_value: u32,
     pub pid_enabled: bool,
@@ -26,7 +26,7 @@ impl Default for ChannelState {
 
 impl ChannelState {
     /// Update PID state on ADC input, calculate new DAC output
-    pub fn update_adc(&mut self, now: Instant, adc_data: i32) {
+    pub fn update_adc(&mut self, now: Instant, adc_data: u32) {
         self.adc_data = Some(adc_data);
         self.adc_time = now;