Work on error correction

Modem/protocol/mp1.c

@@ -3,6 +3,25 @@
 #include <string.h>
 #include <drv/ser.h>
 
+static uint8_t lastByte = 0x00;
+static bool sendParityBlock = false;
+
+INLINE bool BIT(uint8_t byte, int n) { return (byte & BV(n)); }
+static uint8_t mp1ParityBlock(uint8_t first, uint8_t other) {
+	uint8_t parity = 0x00;
+	parity ^= (BIT(first, 1) ^ BIT(first, 2) ^ BIT(first, 4) ^ BIT(first, 5) ^ BIT(first, 7)) << 7;
+	parity ^= (BIT(first, 1) ^ BIT(first, 3) ^ BIT(first, 4) ^ BIT(first, 6) ^ BIT(first, 7)) << 6;
+	parity ^= (BIT(first, 2) ^ BIT(first, 3) ^ BIT(first, 4) ^ BIT(first, 8)) << 5;
+	parity ^= (BIT(first, 5) ^ BIT(first, 6) ^ BIT(first, 7) ^ BIT(first, 8)) << 4;
+
+	parity ^= BIT(other, 1) ^ BIT(other, 2) ^ BIT(other, 4) ^ BIT(other, 5) ^ BIT(other, 7) << 3;
+	parity ^= BIT(other, 1) ^ BIT(other, 3) ^ BIT(other, 4) ^ BIT(other, 6) ^ BIT(other, 7) << 2;
+	parity ^= BIT(other, 2) ^ BIT(other, 3) ^ BIT(other, 4) ^ BIT(other, 8) << 1;
+	parity ^= BIT(other, 5) ^ BIT(other, 6) ^ BIT(other, 7) ^ BIT(other, 8);
+
+	return parity;
+}
+
 static void mp1Decode(MP1 *mp1) {
 	// This decode function is basic and bare minimum.
 	// It does nothing more than extract the data
@@ -31,6 +50,11 @@ void mp1Poll(MP1 *mp1) {
 
 	// Read bytes from the modem until we reach EOF
 	while ((byte = kfile_getc(mp1->modem)) != EOF) {
+		// We have a byte, increment our read counter
+		mp1->readLength++;
+
+		if (mp1->readLength % 3 != 0) {
+			// This is not a parity byte
 			if (!mp1->escape && byte == HDLC_FLAG) {
 				// We are not in an escape sequence and we
 				// found a HDLC_FLAG. This can mean two things:
@@ -52,6 +76,7 @@ void mp1Poll(MP1 *mp1) {
 				// beginning of a frame
 				mp1->reading = true;
 				mp1->packetLength = 0;
+				mp1->readLength = 0;
 				mp1->checksum_in = MP1_CHECKSUM_INIT;
 
 				// We have indicated that we are reading,
@@ -68,6 +93,18 @@ void mp1Poll(MP1 *mp1) {
 				continue;
 			}
 
+			// This should be a parity byte
+			if (mp1->readLength % 3 == 0) {
+				uint8_t calculatedParity = mp1ParityBlock(mp1->buffer[mp1->packetLength-2], mp1->buffer[mp1->packetLength-1]);
+				if (byte == calculatedParity) {
+					// Parity match, block is correct
+				} else {
+					// Parity differ, transmission error ocurred
+					kprintf("Parity mismatch");
+				}
+				mp1->readLength = 0;
+			}
+
 			if (!mp1->escape && byte == AX25_ESC) {
 				// We found an escape character. We'll set
 				// the escape seqeunce indicator so we don't
@@ -94,6 +131,9 @@ void mp1Poll(MP1 *mp1) {
 			// We need to set the escape sequence indicator back
 			// to false after each byte.
 			mp1->escape = false;
+		} else {
+			
+		}
 	}
 
 	if (kfile_error(mp1->modem)) {
@@ -111,10 +151,21 @@ static void mp1Putbyte(MP1 *mp1, uint8_t byte) {
 		byte == HDLC_RESET ||
 		byte == AX25_ESC) {
 		kfile_putc(AX25_ESC, mp1->modem);
+		lastByte = AX25_ESC;
+		sendParityBlock ^= true;
 	}
+
 	kfile_putc(byte, mp1->modem);
+
+	if (sendParityBlock) {
+		kfile_putc(mp1ParityBlock(lastByte, byte), mp1->modem);
+	}
+
+	lastByte = byte;
+	sendParityBlock ^= true;
 }
 
+
 void mp1Send(MP1 *mp1, const void *_buffer, size_t length) {
 	// Get the transmit data buffer
 	const uint8_t *buffer = (const uint8_t *)_buffer;

Modem/protocol/mp1.h

@@ -26,6 +26,7 @@ typedef struct MP1 {
 	uint8_t buffer[MP1_MAX_FRAME_LENGTH];	// A buffer for incoming packets
 	KFile *modem;							// KFile access to the modem
 	size_t packetLength;					// Counter for received packet length
+	size_t readLength;						// This is the full read length, including parity bytes
 	mp1_callback_t callback;				// The function to call when a packet has been received
 	uint8_t checksum_in;					// Rolling checksum for incoming packets
 	uint8_t checksum_out;					// Rolling checksum for outgoing packets

buildrev.h

@@ -1,2 +1,2 @@
-#define VERS_BUILD 577
+#define VERS_BUILD 602
 #define VERS_HOST  "vixen"