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#include <avr/io.h>
#include <stdlib.h>
#include "fecmodem.h"
uint8_t FECModem::parity128(uint8_t byte)
{
return pgm_read_byte(&hammingParityLow[byte & 0x0f]) ^ pgm_read_byte(&hammingParityHigh[byte >> 4]);
}
uint8_t FECModem::parity2416(uint8_t byte1, uint8_t byte2)
{
return parity128(byte1) | (parity128(byte2) << 4);
}
uint8_t FECModem::correct128(uint8_t *byte, uint8_t err)
{
uint8_t result = pgm_read_byte(&hammingParityCheck[err & 0x0f]);
if (result != NO_ERROR) {
if (byte == NULL)
return 3;
if (result == UNCORRECTABLE) {
*byte = 0;
return 3;
}
if (result != ERROR_IN_PARITY) {
*byte ^= result;
}
return 1;
}
return 0;
}
uint8_t FECModem::hamming2416(uint8_t *byte1, uint8_t *byte2, uint8_t parity)
{
uint8_t err;
if (byte1 == NULL || byte2 == NULL) {
return 3;
}
err = parity2416(*byte1, *byte2) ^ parity;
if (err) {
return correct128(byte1, err) + correct128(byte2, err >> 4);
}
return 0;
}
uint8_t FECModem::buffer_available()
{
// XXX this reset implementation is _completely_ broken
// if (newTransmission())
// hammingState = FIRST_BYTE;
if (this->Modem::buffer_available() >= 3)
return 2;
if (hammingState == SECOND_BYTE)
return 1;
return 0;
}
uint8_t FECModem::buffer_get()
{
uint8_t byte1, parity;
if (hammingState == SECOND_BYTE) {
hammingState = FIRST_BYTE;
return buf_byte;
}
hammingState = SECOND_BYTE;
byte1 = this->Modem::buffer_get();
buf_byte = this->Modem::buffer_get();
parity = this->Modem::buffer_get();
hamming2416(&byte1, &buf_byte, parity);
return byte1;
}
FECModem modem;
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