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506 lines
12 KiB
506 lines
12 KiB
/*
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This file is part of VP-Digi.
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VP-Digi is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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VP-Digi is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with VP-Digi. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "ax25.h"
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#include <stdlib.h>
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#include "drivers/modem.h"
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#include "common.h"
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#include "drivers/systick.h"
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enum TxStage
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{
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TX_STAGE_IDLE,
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TX_STAGE_PREAMBLE,
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TX_STAGE_HEADER_FLAGS,
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TX_STAGE_DATA,
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TX_STAGE_CRC,
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TX_STAGE_FOOTER_FLAGS,
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TX_STAGE_TAIL,
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};
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enum TxInitStage
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{
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TX_INIT_OFF,
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TX_INIT_WAITING,
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TX_INIT_TRANSMITTING
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};
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struct TxState
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{
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uint8_t txByte; //current TX byte
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int8_t txBitIdx; //current bit index in txByte
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uint16_t txDelayElapsed; //counter of TXDelay bytes already sent
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uint8_t flagsElapsed; //counter of flag bytes already sent
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uint16_t xmitIdx; //current TX byte index in TX buffer
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uint8_t crcIdx; //currently transmitted byte of CRC
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uint8_t bitstuff; //bit-stuffing counter
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uint16_t txTailElapsed; //counter of TXTail bytes already sent
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uint16_t txDelay; //number of TXDelay bytes to send
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uint16_t txTail; //number of TXTail bytes to send
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uint16_t crc; //current CRC
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uint32_t txQuiet; //quit time + current tick value
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uint8_t txRetries; //number of TX retries
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enum TxInitStage tx; //current TX initialization stage
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enum TxStage txStage; //current TX stage
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};
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volatile struct TxState txState;
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typedef struct
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{
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uint16_t crc; //current CRC
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uint8_t frame[FRAMELEN]; //raw frame buffer
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uint16_t frameIdx; //index for raw frame buffer
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uint8_t recByte; //byte being currently received
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uint8_t rBitIdx; //bit index for recByte
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uint8_t rawData; //raw data being currently received
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RxStage rx; //current RX stage
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uint8_t frameReceived; //frame received flag
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} RxState;
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volatile RxState rxState1, rxState2;
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uint16_t lastCrc = 0; //CRC of the last received frame. If not 0, a frame was successfully received
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uint16_t rxMultiplexDelay = 0; //simple delay for decoder multiplexer to avoid receiving the same frame twice
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RxStage Ax25_getRxStage(uint8_t modemNo)
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{
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if(modemNo == 0)
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return rxState1.rx;
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return rxState2.rx;
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}
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/**
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* @brief Recalculate CRC for one bit
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* @param[in] bit Input bit
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* @param *crc CRC pointer
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*/
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static void ax25_calcCRC(uint8_t bit, uint16_t *crc) {
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static uint16_t xor_result;
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xor_result = *crc ^ bit;
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*crc >>= 1;
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if (xor_result & 0x0001)
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{
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*crc ^= 0x8408;
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}
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return;
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}
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void Ax25_bitParse(uint8_t bit, uint8_t modemNo)
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{
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if(lastCrc > 0) //there was a frame received
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{
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rxMultiplexDelay++;
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if(rxMultiplexDelay > 4) //hold it for a while and wait for the other decoder to receive the frame
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{
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lastCrc = 0;
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rxMultiplexDelay = 0;
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ax25.frameReceived = (rxState1.frameReceived > 0) | ((rxState2.frameReceived > 0) << 1);
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}
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}
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RxState *rx = (RxState*)&rxState1;
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if(modemNo == 1)
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rx = (RxState*)&rxState2;
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rx->rawData <<= 1; //store incoming bit
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rx->rawData |= (bit > 0);
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if(rx->rawData == 0x7E) //HDLC flag received
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{
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if(rx->rx == RX_STAGE_FRAME) //we are in frame, so this is the end of the frame
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{
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if((rx->frameIdx > 15)) //correct frame must be at least 16 bytes long
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{
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uint16_t i = 0;
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for(; i < rx->frameIdx - 2; i++) //look for path end bit
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{
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if(rx->frame[i] & 1)
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break;
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}
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//check if this frame has control=0x03 and PID=0xF0
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//if not, it's not a correct APRS frame, even if it has correct CRC
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if(!((rx->frame[i + 1] == 0x03) && (rx->frame[i + 2] == 0xf0)))
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{
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rx->recByte = 0;
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rx->rBitIdx = 0;
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rx->frameIdx = 0;
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rx->crc = 0xFFFF;
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return;
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}
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if ((rx->frame[rx->frameIdx - 2] == ((rx->crc & 0xFF) ^ 0xFF)) && (rx->frame[rx->frameIdx - 1] == (((rx->crc >> 8) & 0xFF) ^ 0xFF))) //check CRC
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{
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rx->frameReceived = 1;
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if(rx->crc != lastCrc) //the other decoder has not received this frame yet, so store it in main frame buffer
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{
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lastCrc = rx->crc; //store CRC of this frame
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ax25.sLvl = Afsk_getRMS(modemNo); //get RMS amplitude of the received frame
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uint16_t freebuf = 0;
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if(ax25.frameBufWr > ax25.frameBufRd) //check if there is enough free space in buffer
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freebuf = FRAMEBUFLEN - ax25.frameBufWr + ax25.frameBufRd - 3;
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else
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freebuf = ax25.frameBufRd - ax25.frameBufWr - 3;
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if((rx->frameIdx - 2) <= freebuf) //if enough space, store the frame
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{
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for(uint16_t i = 0; i < rx->frameIdx - 2; i++)
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{
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ax25.frameBuf[ax25.frameBufWr++] = rx->frame[i];
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ax25.frameBufWr %= (FRAMEBUFLEN);
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}
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ax25.frameBuf[ax25.frameBufWr++] = 0xFF; //add frame separator
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ax25.frameBufWr %= FRAMEBUFLEN;
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}
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}
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} else
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{
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Afsk_clearRMS(modemNo);
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}
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}
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rx->recByte = 0;
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rx->rBitIdx = 0;
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rx->frameIdx = 0;
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rx->crc = 0xFFFF;
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}
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rx->rx = RX_STAGE_FLAG;
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rx->recByte = 0;
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rx->rBitIdx = 0;
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rx->frameIdx = 0;
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rx->crc = 0xFFFF;
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Afsk_clearRMS(modemNo);
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return;
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}
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if((rx->rawData & 0x7F) == 0x7F) //received 7 consecutive ones, this is an error (sometimes called "escape byte")
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{
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Afsk_clearRMS(modemNo);
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rx->rx = RX_STAGE_IDLE;
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rx->recByte = 0;
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rx->rBitIdx = 0;
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rx->frameIdx = 0;
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rx->crc = 0xFFFF;
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return;
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}
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if(rx->rx == RX_STAGE_IDLE) //not in a frame, don't go further
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return;
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if((rx->rawData & 0x3F) == 0x3E) //dismiss bit 0 added by bitstuffing
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return;
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if(rx->rawData & 0x01) //received bit 1
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rx->recByte |= 0x80; //store it
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if(++rx->rBitIdx >= 8) //received full byte
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{
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if(rx->frameIdx > FRAMELEN) //frame is top long
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{
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rx->rx = RX_STAGE_IDLE;
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rx->recByte = 0;
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rx->rBitIdx = 0;
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rx->frameIdx = 0;
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rx->crc = 0xFFFF;
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Afsk_clearRMS(modemNo);
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}
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if(rx->frameIdx >= 2) //more than 2 bytes received, calculate CRC
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{
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for(uint8_t i = 0; i < 8; i++)
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{
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ax25_calcCRC((rx->frame[rx->frameIdx - 2] >> i) & 0x01, &(rx->crc));
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}
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}
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rx->rx = RX_STAGE_FRAME;
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rx->frame[rx->frameIdx++] = rx->recByte; //store received byte
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rx->recByte = 0;
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rx->rBitIdx = 0;
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}
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else
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rx->recByte >>= 1;
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}
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uint8_t Ax25_getTxBit(void)
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{
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if(txState.txBitIdx == 8)
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{
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txState.txBitIdx = 0;
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if(txState.txStage == TX_STAGE_PREAMBLE) //transmitting preamble (TXDelay)
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{
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if(txState.txDelayElapsed < txState.txDelay) //still transmitting
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{
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txState.txByte = 0x7E;
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txState.txDelayElapsed++;
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}
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else //now transmit initial flags
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{
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txState.txDelayElapsed = 0;
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txState.txStage = TX_STAGE_HEADER_FLAGS;
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}
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}
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if(txState.txStage == TX_STAGE_HEADER_FLAGS) //transmitting initial flags
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{
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if(txState.flagsElapsed < 4) //say we want to transmit 4 flags
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{
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txState.txByte = 0x7E;
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txState.flagsElapsed++;
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}
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else
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{
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txState.flagsElapsed = 0;
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txState.txStage = TX_STAGE_DATA; //transmit data
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}
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}
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if(txState.txStage == TX_STAGE_DATA) //transmitting normal data
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{
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if((ax25.xmitIdx > 10) && (txState.xmitIdx < ax25.xmitIdx)) //send buffer
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{
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if(ax25.frameXmit[txState.xmitIdx] == 0xFF) //frame separator found
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{
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txState.txStage = TX_STAGE_CRC; //transmit CRC
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txState.xmitIdx++;
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}
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else //normal bytes
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{
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txState.txByte = ax25.frameXmit[txState.xmitIdx];
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txState.xmitIdx++;
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}
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} else //end of buffer
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{
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ax25.xmitIdx = 0;
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txState.xmitIdx = 0;
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txState.txStage = TX_STAGE_TAIL;
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}
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}
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if(txState.txStage == TX_STAGE_CRC) //transmitting CRC
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{
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if(txState.crcIdx < 2)
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{
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txState.txByte = (txState.crc >> (txState.crcIdx * 8)) ^ 0xFF;
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txState.crcIdx++;
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}
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else
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{
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txState.crc = 0xFFFF;
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txState.txStage = TX_STAGE_FOOTER_FLAGS; //now transmit flags
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txState.crcIdx = 0;
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}
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}
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if(txState.txStage == TX_STAGE_FOOTER_FLAGS)
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{
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if(txState.flagsElapsed < 8) //say we want to transmit 8 flags
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{
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txState.txByte = 0x7E;
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txState.flagsElapsed++;
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} else
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{
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txState.flagsElapsed = 0;
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txState.txStage = TX_STAGE_DATA; //return to normal data transmission stage. There might be a next frame to transmit
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if((ax25.xmitIdx > 10) && (txState.xmitIdx < ax25.xmitIdx)) //send buffer
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{
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if(ax25.frameXmit[txState.xmitIdx] == 0xFF) //frame separator found
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{
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txState.txStage = TX_STAGE_CRC; //transmit CRC
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txState.xmitIdx++;
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}
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else //normal bytes
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{
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txState.txByte = ax25.frameXmit[txState.xmitIdx];
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txState.xmitIdx++;
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}
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} else //end of buffer
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{
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ax25.xmitIdx = 0;
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txState.xmitIdx = 0;
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txState.txStage = TX_STAGE_TAIL;
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}
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}
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}
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if(txState.txStage == TX_STAGE_TAIL) //transmitting tail
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{
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ax25.xmitIdx = 0;
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if(txState.txTailElapsed < txState.txTail)
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{
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txState.txByte = 0x7E;
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txState.txTailElapsed++;
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}
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else //tail transmitted, stop transmissiob
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{
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txState.txTailElapsed = 0;
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txState.txStage = TX_STAGE_IDLE;
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txState.crc = 0xFFFF;
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txState.bitstuff = 0;
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txState.txByte = 0;
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txState.tx = TX_INIT_OFF;
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Afsk_transmitStop();
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}
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}
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}
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uint8_t txBit = 0;
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if((txState.txStage == TX_STAGE_DATA) || (txState.txStage == TX_STAGE_CRC)) //transmitting normal data or CRC
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{
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if(txState.bitstuff == 5) //5 consecutive ones transmitted
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{
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txBit = 0; //transmit bit-stuffed 0
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txState.bitstuff = 0;
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}
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else
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{
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if(txState.txByte & 1) //1 being transmitted
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{
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txState.bitstuff++; //increment bit stuffing counter
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txBit = 1;
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} else
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{
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txBit = 0;
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txState.bitstuff = 0; //0 being transmitted, reset bit stuffing counter
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}
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if(txState.txStage == TX_STAGE_DATA) //calculate CRC only for normal data
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ax25_calcCRC(txState.txByte & 1, (uint16_t*)&(txState.crc));
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txState.txByte >>= 1;
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txState.txBitIdx++;
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}
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}
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else //transmitting preambles or flags, don't calculate CRC, don't use bit stuffing
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{
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txBit = txState.txByte & 1;
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txState.txByte >>= 1;
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txState.txBitIdx++;
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}
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return txBit;
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}
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/**
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* @brief Initialize transmission and start when possible
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*/
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void Ax25_transmitBuffer(void)
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{
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if(txState.tx == TX_INIT_WAITING)
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return;
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if(txState.tx == TX_INIT_TRANSMITTING)
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return;
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if(ax25.xmitIdx > 10)
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{
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txState.txQuiet = (ticks + (ax25Cfg.quietTime / 10) + rando(0, 20)); //calculate required delay
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txState.tx = TX_INIT_WAITING;
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}
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else ax25.xmitIdx = 0;
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}
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/**
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* @brief Start transmissin immediately
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* @warning Transmission should be initialized using Ax25_transmitBuffer
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*/
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static void ax25_transmitStart(void)
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{
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txState.crc = 0xFFFF; //initial CRC value
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txState.txStage = TX_STAGE_PREAMBLE;
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txState.txByte = 0;
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txState.txBitIdx = 0;
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Afsk_transmitStart();
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}
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/**
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* @brief Start transmitting when possible
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* @attention Must be continuously polled in main loop
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*/
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void Ax25_transmitCheck(void)
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{
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if(txState.tx == TX_INIT_OFF) //TX not initialized at all, nothing to transmit
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return;
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if(txState.tx == TX_INIT_TRANSMITTING) //already transmitting
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return;
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if(ax25.xmitIdx < 10)
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{
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ax25.xmitIdx = 0;
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return;
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}
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if(Afsk_isTxTestOngoing()) //TX test is enabled, wait for now
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return;
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if(txState.txQuiet < ticks) //quit time has elapsed
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{
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if(!Afsk_dcdState()) //channel is free
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{
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txState.tx = TX_INIT_TRANSMITTING; //transmit right now
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txState.txRetries = 0;
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ax25_transmitStart();
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}
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else //channel is busy
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{
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if(txState.txRetries == 8) //8th retry occured, transmit immediately
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{
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txState.tx = TX_INIT_TRANSMITTING; //transmit right now
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txState.txRetries = 0;
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ax25_transmitStart();
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}
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else //still trying
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{
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txState.txQuiet = ticks + rando(10, 50); //try again after some random time
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txState.txRetries++;
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}
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}
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}
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}
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void Ax25_init(void)
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{
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txState.crc = 0xFFFF;
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ax25.frameBufWr = 0;
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ax25.frameBufRd = 0;
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ax25.xmitIdx = 0;
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ax25.frameReceived = 0;
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rxState1.crc = 0xFFFF;
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rxState2.crc = 0xFFFF;
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txState.txDelay = ((float)ax25Cfg.txDelayLength / 6.66667f); //change milliseconds to byte count
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txState.txTail = ((float)ax25Cfg.txTailLength / 6.66667f);
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}
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