OpenModem/protocol/KISS.c

#include <stdlib.h>
#include <string.h>

#include "device.h"
#include "KISS.h"

static uint8_t serialBuffer[AX25_MAX_FRAME_LEN]; // Buffer for holding incoming serial data
AX25Ctx *ax25ctx;
Afsk *channel;
Serial *serial;
size_t frame_len;
bool IN_FRAME;
bool ESCAPE;

uint8_t command = CMD_UNKNOWN;
unsigned long custom_preamble = CONFIG_AFSK_PREAMBLE_LEN;
unsigned long custom_tail = CONFIG_AFSK_TRAILER_LEN;

unsigned long slotTime = 200;
uint8_t p = 63;

void kiss_init(AX25Ctx *ax25, Afsk *afsk, Serial *ser) {
    ax25ctx = ax25;
    serial = ser;
    channel = afsk;
}

void kiss_messageCallback(AX25Ctx *ctx) {
    fputc(FEND, &serial->uart0);
    fputc(0x00, &serial->uart0);
    for (unsigned i = 0; i < ctx->frame_len-2; i++) {
        uint8_t b = ctx->buf[i];
        if (b == FEND) {
            fputc(FESC, &serial->uart0);
            fputc(TFEND, &serial->uart0);
        } else if (b == FESC) {
            fputc(FESC, &serial->uart0);
            fputc(TFESC, &serial->uart0);
        } else {
            fputc(b, &serial->uart0);
        }
    }
    fputc(FEND, &serial->uart0);
}

void kiss_csma(AX25Ctx *ctx, uint8_t *buf, size_t len) {
    bool sent = false;
    while (!sent) {
        //puts("Waiting in CSMA");
        if(!channel->hdlc.receiving) {
            uint8_t tp = rand() & 0xFF;
            if (tp < p) {
                ax25_sendRaw(ctx, buf, len);
                sent = true;
            } else {
                ticks_t start = timer_clock();
                long slot_ticks = ms_to_ticks(slotTime);
                while (timer_clock() - start < slot_ticks) {
                    cpu_relax();
                }
            }
        } else {
            while (!sent && channel->hdlc.receiving) {
                // Continously poll the modem for data
                // while waiting, so we don't overrun
                // receive buffers
                ax25_poll(ax25ctx);

                if (channel->status != 0) {
                    // If an overflow or other error
                    // occurs, we'll back off and drop
                    // this packet silently.
                    channel->status = 0;
                    sent = true;
                }
            }
        }

    }
    
}

void kiss_serialCallback(uint8_t sbyte) {
    if (IN_FRAME && sbyte == FEND && command == CMD_DATA) {
        IN_FRAME = false;
        kiss_csma(ax25ctx, serialBuffer, frame_len);
    } else if (sbyte == FEND) {
        IN_FRAME = true;
        command = CMD_UNKNOWN;
        frame_len = 0;
    } else if (IN_FRAME && frame_len < AX25_MAX_FRAME_LEN) {
        // Have a look at the command byte first
        if (frame_len == 0 && command == CMD_UNKNOWN) {
            // MicroModem supports only one HDLC port, so we
            // strip off the port nibble of the command byte
            sbyte = sbyte & 0x0F;
            command = sbyte;
        } else if (command == CMD_DATA) {
            if (sbyte == FESC) {
                ESCAPE = true;
            } else {
                if (ESCAPE) {
                    if (sbyte == TFEND) sbyte = FEND;
                    if (sbyte == TFESC) sbyte = FESC;
                    ESCAPE = false;
                }
                serialBuffer[frame_len++] = sbyte;
            }
        } else if (command == CMD_TXDELAY) {
            custom_preamble = sbyte * 10UL;
        } else if (command == CMD_TXTAIL) {
            custom_tail = sbyte * 10;
        } else if (command == CMD_SLOTTIME) {
            slotTime = sbyte * 10;
        } else if (command == CMD_P) {
            p = sbyte;
        } 
        
    }
}