fix(dust-sensor): validate UART firmware setup

Author: thisisanubhav

lib/communication/peripherals/uart.dart

@@ -32,7 +32,12 @@ class Uart2 {
     packetHandler.sendByte(_commands.uart2);
     packetHandler.sendByte(_commands.setBaud);
     packetHandler.sendInt(divider);
-    await packetHandler.getAcknowledgement();
+    final acknowledgement = await packetHandler.getAcknowledgement();
+    if (acknowledgement != 1) {
+      throw StateError(
+        'UART2 rejected baud-rate configuration (ACK $acknowledgement)',
+      );
+    }
   }
 
   Future<bool> hasData() async {

lib/providers/dust_sensor_state_provider.dart

@@ -93,6 +93,7 @@ class Sds011DustSensorSource implements DustSensorSource {
 
   final ScienceLab scienceLab;
   Uart2? _uart;
+  int? _uartFirmwareMajor;
   final Sds011FrameParser _parser = Sds011FrameParser();
 
   Sds011DustSensorSource(this.scienceLab);
@@ -103,10 +104,17 @@ class Sds011DustSensorSource implements DustSensorSource {
   @override
   Future<void> initialize() async {
     final firmwareMajor = getIt.get<BoardStateProvider>().pslabFirmwareVersion;
-    final uart = _uart ??= Uart2(
-      scienceLab.mPacketHandler,
-      requiresWriteAcknowledgement: firmwareMajor > 0 && firmwareMajor < 3,
-    );
+    if (firmwareMajor == 0) {
+      throw StateError('Unable to determine the PSLab firmware version');
+    }
+    if (_uart == null || _uartFirmwareMajor != firmwareMajor) {
+      _uart = Uart2(
+        scienceLab.mPacketHandler,
+        requiresWriteAcknowledgement: firmwareMajor < 3,
+      );
+      _uartFirmwareMajor = firmwareMajor;
+    }
+    final uart = _uart!;
     await uart.configure(baudRate);
   }
 

test/uart_test.dart

@@ -65,6 +65,12 @@ void main() {
     expect(handler.writes, [5, 4, 0x82, 0x06]);
   });
 
+  test('rejects a failed baud-rate acknowledgement', () async {
+    handler.responses.add(3);
+
+    await expectLater(uart.configure(9600), throwsStateError);
+  });
+
   test('reads UART status and one byte without bulk length fields', () async {
     handler.responses.addAll([1, 0xaa]);