From ae3bfffd2829228d00d02ca1cbf5df8a899f7fb3 Mon Sep 17 00:00:00 2001 From: Mark Qvist Date: Sun, 13 Apr 2014 17:25:13 +0200 Subject: [PATCH] Work on error correction --- Modem/protocol/mp1.c | 169 ++++++++++++++++++++++++++++--------------- Modem/protocol/mp1.h | 1 + buildrev.h | 2 +- 3 files changed, 112 insertions(+), 60 deletions(-) diff --git a/Modem/protocol/mp1.c b/Modem/protocol/mp1.c index c8d1017..612ba05 100644 --- a/Modem/protocol/mp1.c +++ b/Modem/protocol/mp1.c @@ -3,6 +3,25 @@ #include #include +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 @@ -31,69 +50,90 @@ void mp1Poll(MP1 *mp1) { // Read bytes from the modem until we reach EOF while ((byte = kfile_getc(mp1->modem)) != EOF) { - if (!mp1->escape && byte == HDLC_FLAG) { - // We are not in an escape sequence and we - // found a HDLC_FLAG. This can mean two things: - if (mp1->packetLength >= MP1_MIN_FRAME_LENGTH) { - // We already have more data than the minimum - // frame length, which means the flag signifies - // the end of the packet. Pass control to the - // decoder. - if ((mp1->checksum_in & 0xff) == 0x00) { - mp1Decode(mp1); + // 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: + if (mp1->packetLength >= MP1_MIN_FRAME_LENGTH) { + // We already have more data than the minimum + // frame length, which means the flag signifies + // the end of the packet. Pass control to the + // decoder. + if ((mp1->checksum_in & 0xff) == 0x00) { + mp1Decode(mp1); + } else { + // Checksum was incorrect, we don't do anything, + // but you can enable the decode anyway, if you + // need it for testing or debugging + // mp1Decode(mp1); + } + } + // If the above is not the case, this must be the + // 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, + // and reset the length counter. Now we'll + // continue to the next byte. + continue; + } + + if (!mp1->escape && byte == HDLC_RESET) { + // Not good, we got a reset. The transmitting + // party may have encountered an error. We'll + // stop receiving this packet immediately. + mp1->reading = false; + 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 { - // Checksum was incorrect, we don't do anything, - // but you can enable the decode anyway, if you - // need it for testing or debugging - // mp1Decode(mp1); + // 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 + // interpret the next byte as a reset or flag + mp1->escape = true; + continue; + } + + // Now let's get to the actual reading of the data + if (mp1->reading) { + if (mp1->packetLength < MP1_MAX_FRAME_LENGTH) { + // If the length of the current incoming frame is + // still less than our max length, put the incoming + // byte in the buffer. + if (!mp1->escape) mp1->checksum_in = mp1->checksum_in ^ byte; + mp1->buffer[mp1->packetLength++] = byte; + } else { + // If not, we have a problem: The buffer has overrun + // We need to stop receiving, and the packet will be + // dropped :( + mp1->reading = false; } } - // If the above is not the case, this must be the - // beginning of a frame - mp1->reading = true; - mp1->packetLength = 0; - mp1->checksum_in = MP1_CHECKSUM_INIT; - - // We have indicated that we are reading, - // and reset the length counter. Now we'll - // continue to the next byte. - continue; + // We need to set the escape sequence indicator back + // to false after each byte. + mp1->escape = false; + } else { + } - - if (!mp1->escape && byte == HDLC_RESET) { - // Not good, we got a reset. The transmitting - // party may have encountered an error. We'll - // stop receiving this packet immediately. - mp1->reading = false; - continue; - } - - if (!mp1->escape && byte == AX25_ESC) { - // We found an escape character. We'll set - // the escape seqeunce indicator so we don't - // interpret the next byte as a reset or flag - mp1->escape = true; - continue; - } - - // Now let's get to the actual reading of the data - if (mp1->reading) { - if (mp1->packetLength < MP1_MAX_FRAME_LENGTH) { - // If the length of the current incoming frame is - // still less than our max length, put the incoming - // byte in the buffer. - if (!mp1->escape) mp1->checksum_in = mp1->checksum_in ^ byte; - mp1->buffer[mp1->packetLength++] = byte; - } else { - // If not, we have a problem: The buffer has overrun - // We need to stop receiving, and the packet will be - // dropped :( - mp1->reading = false; - } - } - // We need to set the escape sequence indicator back - // to false after each byte. - mp1->escape = false; } 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; diff --git a/Modem/protocol/mp1.h b/Modem/protocol/mp1.h index 289a25a..0887d4e 100644 --- a/Modem/protocol/mp1.h +++ b/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 diff --git a/buildrev.h b/buildrev.h index 75e6e0a..f77a343 100644 --- a/buildrev.h +++ b/buildrev.h @@ -1,2 +1,2 @@ -#define VERS_BUILD 577 +#define VERS_BUILD 602 #define VERS_HOST "vixen"