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Protocol-level (12,8) hamming code implemented

This commit is contained in:
Mark Qvist 2014-04-14 01:23:48 +02:00
parent ae3bfffd28
commit b2d2def862
3 changed files with 156 additions and 93 deletions
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119
Modem/protocol/mp1.c
View File

@ -3,21 +3,24 @@
#include <string.h>
#include <drv/ser.h>
// FIXME: Describe these
static uint8_t lastByte = 0x00;
static bool sendParityBlock = false;
INLINE bool BIT(uint8_t byte, int n) { return (byte & BV(n)); }
// FIXME: Describe this
INLINE bool BIT(uint8_t byte, int n) { return ((byte & BV(n-1))>>(n-1)); }
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);
parity = ((BIT(first, 1) ^ BIT(first, 2) ^ BIT(first, 4) ^ BIT(first, 5) ^ BIT(first, 7))) +
((BIT(first, 1) ^ BIT(first, 3) ^ BIT(first, 4) ^ BIT(first, 6) ^ BIT(first, 7))<<1) +
((BIT(first, 2) ^ BIT(first, 3) ^ BIT(first, 4) ^ BIT(first, 8))<<2) +
((BIT(first, 5) ^ BIT(first, 6) ^ BIT(first, 7) ^ BIT(first, 8))<<3) +
((BIT(other, 1) ^ BIT(other, 2) ^ BIT(other, 4) ^ BIT(other, 5) ^ BIT(other, 7))<<4) +
((BIT(other, 1) ^ BIT(other, 3) ^ BIT(other, 4) ^ BIT(other, 6) ^ BIT(other, 7))<<5) +
((BIT(other, 2) ^ BIT(other, 3) ^ BIT(other, 4) ^ BIT(other, 8))<<6) +
((BIT(other, 5) ^ BIT(other, 6) ^ BIT(other, 7) ^ BIT(other, 8))<<7);
return parity;
}
@ -30,9 +33,19 @@ static void mp1Decode(MP1 *mp1) {
MP1Packet packet; // A decoded packet struct
uint8_t *buffer = mp1->buffer; // Get the buffer from the protocol context
// Get the header and "remove" it from the buffer
uint8_t header = buffer[0];
buffer++;
// If header indicates a padded packet, remove
// padding
if (header & 0x01) {
buffer++;
}
// Set the payload length of the packet to the counted
// length minus 1, so we remove the checksum
packet.dataLength = mp1->packetLength - 1;
packet.dataLength = mp1->packetLength - 2 - (header & 0x01);
packet.data = buffer;
// If a callback have been specified, let's
@ -47,14 +60,54 @@ static void mp1Decode(MP1 *mp1) {
////////////////////////////////////////////////////////////
void mp1Poll(MP1 *mp1) {
int byte; // A place to store our read byte
sendParityBlock = false; // Reset our parity tx indicator
// Read bytes from the modem until we reach EOF
while ((byte = kfile_getc(mp1->modem)) != EOF) {
// We have a byte, increment our read counter
// FIXME: Describe error correction
if (mp1->reading && (byte != AX25_ESC) ) {
mp1->readLength++;
if (mp1->readLength % 3 != 0) {
// This is not a parity byte
if (mp1->readLength % 3 == 0) {
mp1->calculatedParity = mp1ParityBlock(mp1->buffer[mp1->packetLength-2], mp1->buffer[mp1->packetLength-1]);
uint8_t syndrome = mp1->calculatedParity ^ byte;
if (syndrome == 0x00) {
// No problems!
} else {
uint8_t syndromes[2];
syndromes[0] = syndrome & 0x0f;
syndromes[1] = (syndrome & 0xf0) >> 4;
for (int i = 0; i < 2; i++) {
uint8_t s = syndromes[i];
uint8_t correction = 0x00;
if (s == 1 || s == 2 || s == 4 || s == 8) {
// Error in parity bit, no correction needed
continue;
}
if (s == 3) correction = 0x01;
if (s == 5) correction = 0x02;
if (s == 6) correction = 0x04;
if (s == 7) correction = 0x08;
if (s == 9) correction = 0x10;
if (s == 10) correction = 0x20;
if (s == 11) correction = 0x40;
if (s == 12) correction = 0x80;
if (correction != 0x00) {
mp1->checksum_in ^= correction;
}
mp1->buffer[mp1->packetLength-(2-i)] ^= correction;
}
}
continue;
}
}
// FIXME: Describe error correction //////////
if (!mp1->escape && byte == HDLC_FLAG) {
// We are not in an escape sequence and we
// found a HDLC_FLAG. This can mean two things:
@ -64,12 +117,14 @@ void mp1Poll(MP1 *mp1) {
// the end of the packet. Pass control to the
// decoder.
if ((mp1->checksum_in & 0xff) == 0x00) {
kprintf("[OK] ");
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);
kprintf("[ER] [%d] ", mp1->checksum_in);
mp1Decode(mp1);
}
}
// If the above is not the case, this must be the
@ -94,16 +149,6 @@ void mp1Poll(MP1 *mp1) {
}
// 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
@ -119,7 +164,7 @@ void mp1Poll(MP1 *mp1) {
// 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->checksum_in = mp1->checksum_in ^ byte;
mp1->buffer[mp1->packetLength++] = byte;
} else {
// If not, we have a problem: The buffer has overrun
@ -128,12 +173,10 @@ void mp1Poll(MP1 *mp1) {
mp1->reading = false;
}
}
// We need to set the escape sequence indicator back
// to false after each byte.
mp1->escape = false;
} else {
}
}
if (kfile_error(mp1->modem)) {
@ -143,6 +186,7 @@ void mp1Poll(MP1 *mp1) {
}
}
// FIXME: Desribe additions here
static void mp1Putbyte(MP1 *mp1, uint8_t byte) {
// If we are sending something that looks
// like an HDLC special byte, send an escape
@ -152,20 +196,20 @@ static void mp1Putbyte(MP1 *mp1, uint8_t byte) {
byte == AX25_ESC) {
kfile_putc(AX25_ESC, mp1->modem);
lastByte = AX25_ESC;
sendParityBlock ^= true;
//sendParityBlock ^= true;
}
kfile_putc(byte, mp1->modem);
if (sendParityBlock) {
kfile_putc(mp1ParityBlock(lastByte, byte), mp1->modem);
uint8_t p = mp1ParityBlock(lastByte, byte);
kfile_putc(p, 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;
@ -176,6 +220,21 @@ void mp1Send(MP1 *mp1, const void *_buffer, size_t length) {
// Transmit the HDLC_FLAG to signify start of TX
kfile_putc(HDLC_FLAG, mp1->modem);
// Write header and possibly padding
// Remember we also write a header and
// a checksum. This ensures that we will
// always end our packet with a checksum
// and a parity byte.
if (length % 2 != 0) {
mp1->checksum_out = mp1->checksum_out ^ 0xf1;
mp1Putbyte(mp1, 0xf1);
mp1->checksum_out = mp1->checksum_out ^ 0x55;
mp1Putbyte(mp1, 0x55);
} else {
mp1->checksum_out = mp1->checksum_out ^ 0xf0;
mp1Putbyte(mp1, 0xf0);
}
// Continously increment the pointer address
// of the buffer while passing it to the byte
// output function

4
Modem/protocol/mp1.h
View File

@ -24,14 +24,17 @@ typedef void (*mp1_callback_t)(struct MP1Packet *packet);
// Struct for a protocol context
typedef struct MP1 {
uint8_t buffer[MP1_MAX_FRAME_LENGTH]; // A buffer for incoming packets
uint8_t fecBuffer[3]; // FEC buffer
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
uint8_t calculatedParity; // Calculated parity for incoming data block
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
bool reading; // True when we have seen a HDLC flag
bool escape; // We need to know if we are in an escape sequence
bool fecEscape; // fec escape
} MP1;
// A struct encapsulating a network packet
@ -41,6 +44,7 @@ typedef struct MP1Packet {
} MP1Packet;
void mp1Init(MP1 *mp1, KFile *modem, mp1_callback_t callback);
void mp1Read(MP1 *mp1, int byte);
void mp1Poll(MP1 *mp1);
void mp1Send(MP1 *mp1, const void *_buffer, size_t length);

2
buildrev.h
View File

@ -1,2 +1,2 @@
#define VERS_BUILD 602
#define VERS_BUILD 829
#define VERS_HOST "vixen"