eculocate

commit cf1f5dcde34b7e85505a2bdd0e9bd0b77d0e68a2
parent 2b96e079bc872e221361b5a9513b4f7ccfd5d973
Author: Daniel Barlow <dan@telent.net>
Date:   Fri, 21 Nov 2025 23:52:29 +0000

calculate checksum on outgoing packets

Diffstat:
M
src/ecu.rs
 | 
29
+++++++++++++++++++++++++----

1 file changed, 25 insertions(+), 4 deletions(-)
diff --git a/src/ecu.rs b/src/ecu.rs
@@ -28,9 +28,23 @@ impl Ecu<'_> {
 	}
     }
 
+    fn checksum(bytes: &mut [u8]) -> bool {
+	let last = bytes.len() - 1;
+	let mut sum : u8 = 0;
+	for b in &bytes[0..last] {
+	    sum = sum.wrapping_add(*b);
+	}
+	sum = 0u8 - sum;
+	let is_correct = sum == bytes[last];
+	bytes[last] = sum;
+	is_correct
+    }
+
+
     async fn chat<'z>(uart: &mut Uart<'_, Async>,
-		  send: &[u8],
-		  receive: &'z mut [u8]) -> &'z [u8] {
+		      send: &mut [u8],
+		      receive: &'z mut [u8]) -> &'z [u8] {
+	let _ = Self::checksum(send);
 	uart.write(send).expect("write failed");
 	let _ = uart.flush();
 	let mut received = 0;
@@ -78,9 +92,16 @@ impl Ecu<'_> {
 	    .into_async();
 
 	let mut buf = [0u8; 80];
-	let _ = Self::chat(&mut uart, b"\xfe\x04\xff\xff", &mut buf[0..0]).await;
+
+	let _ = Self::chat(&mut uart,
+			   &mut [0xfe, 0x04, 0xff, 0xff],
+			   &mut buf[0..0]).await;
 	Timer::after_millis(200).await;
-	let handshake = Self::chat(&mut uart, b"\x72\x05\x00\xF0\x99", &mut buf[0..4]).await;
+
+	// checksum is also correct on this packet
+	let handshake = Self::chat(&mut uart,
+				   &mut [0x72, 0x05, 0x00, 0xF0, 0x99],
+				   &mut buf[0..4]).await;
 	info!("matches {}", handshake == b"\x02\x04\x00\xfa");
     }