LibAPRS/src/AX25.cpp

// Based on work by Francesco Sacchi

#include "Arduino.h"
#include <string.h>
#include <ctype.h>
#include "AX25.h"
#include "HDLC.h"
#include "CRC-CCIT.h"
#include "AFSK.h"

#define countof(a) sizeof(a)/sizeof(a[0])
#define MIN(a,b) ({ typeof(a) _a = (a); typeof(b) _b = (b); ((typeof(_a))((_a < _b) ? _a : _b)); })
#define DECODE_CALL(buf, addr) for (unsigned i = 0; i < sizeof((addr))-CALL_OVERSPACE; i++) { char c = (*(buf)++ >> 1); (addr)[i] = (c == ' ') ? '\x0' : c; }
#define AX25_SET_REPEATED(msg, idx, val) do { if (val) { (msg)->rpt_flags |= _BV(idx); } else { (msg)->rpt_flags &= ~_BV(idx) ; } } while(0)

extern int LibAPRS_vref;
extern bool LibAPRS_open_squelch;

void ax25_init(AX25Ctx *ctx, ax25_callback_t hook) {
    memset(ctx, 0, sizeof(*ctx));
    ctx->hook = hook;
    ctx->crc_in = ctx->crc_out = CRC_CCIT_INIT_VAL;
}

static void ax25_decode(AX25Ctx *ctx) {
    AX25Msg msg;
    uint8_t *buf = ctx->buf;

    DECODE_CALL(buf, msg.dst.call);
    msg.dst.ssid = (*buf++ >> 1) & 0x0F;
    msg.dst.call[6] = 0;

    DECODE_CALL(buf, msg.src.call);
    msg.src.ssid = (*buf >> 1) & 0x0F;
    msg.src.call[6] = 0;

    for (msg.rpt_count = 0; !(*buf++ & 0x01) && (msg.rpt_count < countof(msg.rpt_list)); msg.rpt_count++) {
        DECODE_CALL(buf, msg.rpt_list[msg.rpt_count].call);
        //db1sb: terminate rpt_list.call-entries
        msg.rpt_list[msg.rpt_count].call[6] = 0; 
        msg.rpt_list[msg.rpt_count].ssid = (*buf >> 1) & 0x0F;
        AX25_SET_REPEATED(&msg, msg.rpt_count, (*buf & 0x80));
    }

    msg.ctrl = *buf++;
    if (msg.ctrl != AX25_CTRL_UI) { return; }

    msg.pid = *buf++;
    if (msg.pid != AX25_PID_NOLAYER3) { return; }

    msg.len = ctx->frame_len - 2 - (buf - ctx->buf);
    msg.info = buf;

    if (ctx->hook) {
        cli();
        ctx->hook(&msg);
        sei();
    }   

}

void ax25_poll(AX25Ctx *ctx) {
    int c;

    while ((c = afsk_getchar()) != EOF) {
        if (!ctx->escape && c == HDLC_FLAG) {
            if (ctx->frame_len >= AX25_MIN_FRAME_LEN) {
                if (ctx->crc_in == AX25_CRC_CORRECT) {
                    if(LibAPRS_open_squelch) {
                        LED_RX_ON();
                    }
                    ax25_decode(ctx);
                }
            }
            ctx->sync = true;
            ctx->crc_in = CRC_CCIT_INIT_VAL;
            ctx->frame_len = 0;
            continue;
        }

        if (!ctx->escape && c == HDLC_RESET) {
            ctx->sync = false;
            continue;
        }

        if (!ctx->escape && c == AX25_ESC) {
            ctx->escape = true;
            continue;
        }

        if (ctx->sync) {
            if (ctx->frame_len < AX25_MAX_FRAME_LEN) {
                ctx->buf[ctx->frame_len++] = c;
                ctx->crc_in = update_crc_ccit(c, ctx->crc_in);
            } else {
                ctx->sync = false;
            }
        }
        ctx->escape = false;
    }
}

static void ax25_putchar(AX25Ctx *ctx, uint8_t c)
{
    if (c == HDLC_FLAG || c == HDLC_RESET || c == AX25_ESC) afsk_putchar(AX25_ESC);
    ctx->crc_out = update_crc_ccit(c, ctx->crc_out);
    afsk_putchar(c);
}

void ax25_sendRaw(AX25Ctx *ctx, void *_buf, size_t len) {
    ctx->crc_out = CRC_CCIT_INIT_VAL;
    afsk_putchar(HDLC_FLAG);
    const uint8_t *buf = (const uint8_t *)_buf;
    while (len--) ax25_putchar(ctx, *buf++);

    uint8_t crcl = (ctx->crc_out & 0xff) ^ 0xff;
    uint8_t crch = (ctx->crc_out >> 8) ^ 0xff;
    ax25_putchar(ctx, crcl);
    ax25_putchar(ctx, crch);

    afsk_putchar(HDLC_FLAG);
}

static void ax25_sendCall(AX25Ctx *ctx, const AX25Call *addr, bool last){
    unsigned len = MIN((sizeof(addr->call) - CALL_OVERSPACE), strlen(addr->call));

    for (unsigned i = 0; i < len; i++) {
        uint8_t c = addr->call[i];
        c = toupper(c);
        ax25_putchar(ctx, c << 1);
    }

    if (len < (sizeof(addr->call) - CALL_OVERSPACE)) {
        for (unsigned i = 0; i < (sizeof(addr->call) - CALL_OVERSPACE) - len; i++) {
            ax25_putchar(ctx, ' ' << 1);
        }
    }

    uint8_t ssid = 0x60 | (addr->ssid << 1) | (last ? 0x01 : 0);
    ax25_putchar(ctx, ssid);
}

void ax25_sendVia(AX25Ctx *ctx, const AX25Call *path, size_t path_len, const void *_buf, size_t len) {
    const uint8_t *buf = (const uint8_t *)_buf;

    ctx->crc_out = CRC_CCIT_INIT_VAL;
    afsk_putchar(HDLC_FLAG);

    for (size_t i = 0; i < path_len; i++) {
        ax25_sendCall(ctx, &path[i], (i == path_len - 1));
    }

    ax25_putchar(ctx, AX25_CTRL_UI);
    ax25_putchar(ctx, AX25_PID_NOLAYER3);

    while (len--) {
        ax25_putchar(ctx, *buf++);
    }

    uint8_t crcl = (ctx->crc_out & 0xff) ^ 0xff;
    uint8_t crch = (ctx->crc_out >> 8) ^ 0xff;
    ax25_putchar(ctx, crcl);
    ax25_putchar(ctx, crch);

    afsk_putchar(HDLC_FLAG);
}