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Work on error correction

This commit is contained in:
Mark Qvist 2014-04-13 17:25:13 +02:00
parent 13af4dcd2b
commit ae3bfffd28
3 changed files with 112 additions and 60 deletions
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167
Modem/protocol/mp1.c
View File

@ -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
@ -31,69 +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 need to set the escape sequence indicator back
// to false after each byte.
mp1->escape = false;
} else {
// 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;
}
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;

1
Modem/protocol/mp1.h
View File

@ -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

2
buildrev.h
View File

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