ax25.c

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#include "ax25.h"
#include "cfg/cfg_ax25.h"

#include <algo/crc_ccitt.h>

#define LOG_LEVEL  AX25_LOG_LEVEL
#define LOG_FORMAT AX25_LOG_FORMAT
#include <cfg/log.h>

#include <string.h> //memset, memcmp
#include <ctype.h>  //isalnum, toupper

#define DECODE_CALL(buf, addr) \
    for (unsigned i = 0; i < sizeof((addr)); i++) \
    { \
        (addr)[i] = *(buf)++ >> 1; \
    }

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;

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

    LOG_INFO("SRC[%.6s-%d], DST[%.6s-%d]\n", msg.src.call, msg.src.ssid, msg.dst.call, msg.dst.ssid);

    /* Repeater addresses */
    #if CONFIG_AX25_RPT_LST
        for (msg.rpt_cnt = 0; !(*buf++ & 0x01) && (msg.rpt_cnt < countof(msg.rpt_lst)); msg.rpt_cnt++)
        {
            DECODE_CALL(buf, msg.rpt_lst[msg.rpt_cnt].call);
            msg.rpt_lst[msg.rpt_cnt].ssid = (*buf >> 1) & 0x0F;
            LOG_INFO("RPT%d[%.6s-%d]\n", msg.rpt_cnt, msg.rpt_lst[msg.rpt_cnt].call, msg.rpt_lst[msg.rpt_cnt].ssid);
        }
    #else
        while (!(*buf++ & 0x01))
        {
            char rpt[6];
            uint8_t ssid;
            DECODE_CALL(buf, rpt);
            ssid = (*buf >> 1) & 0x0F;
            LOG_INFO("RPT[%.6s-%d]\n", rpt, ssid);
        }
    #endif

    msg.ctrl = *buf++;
    if (msg.ctrl != AX25_CTRL_UI)
    {
        LOG_WARN("Only UI frames are handled, got [%02X]\n", msg.ctrl);
        return;
    }

    msg.pid = *buf++;
    if (msg.pid != AX25_PID_NOLAYER3)
    {
        LOG_WARN("Only frames without layer3 protocol are handled, got [%02X]\n", msg.pid);
        return;
    }

    msg.len = ctx->frm_len - 2 - (buf - ctx->buf);
    msg.info = buf;
    LOG_INFO("DATA: %.*s\n", msg.len, msg.info);

    if (ctx->hook)
        ctx->hook(&msg);
}


void ax25_poll(AX25Ctx *ctx)
{
    int c;

    while ((c = kfile_getc(ctx->ch)) != EOF)
    {
        if (!ctx->escape && c == HDLC_FLAG)
        {
            if (ctx->frm_len >= AX25_MIN_FRAME_LEN)
            {
                if (ctx->crc_in == AX25_CRC_CORRECT)
                {
                    LOG_INFO("Frame found!\n");
                    ax25_decode(ctx);
                }
                else
                {
                    LOG_INFO("CRC error, computed [%04X]\n", ctx->crc_in);
                }
            }
            ctx->sync = true;
            ctx->crc_in = CRC_CCITT_INIT_VAL;
            ctx->frm_len = 0;
            continue;
        }

        if (!ctx->escape && c == HDLC_RESET)
        {
            LOG_INFO("HDLC reset\n");
            ctx->sync = false;
            continue;
        }

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

        if (ctx->sync)
        {
            if (ctx->frm_len < CONFIG_AX25_FRAME_BUF_LEN)
            {
                ctx->buf[ctx->frm_len++] = c;
                ctx->crc_in = updcrc_ccitt(c, ctx->crc_in);
            }
            else
            {
                LOG_INFO("Buffer overrun");
                ctx->sync = false;
            }
        }
        ctx->escape = false;
    }

    if (kfile_error(ctx->ch))
    {
        LOG_ERR("Channel error [%04x]\n", kfile_error(ctx->ch));
        kfile_clearerr(ctx->ch);
    }
}

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

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

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

    /* Fill with spaces the rest of the CALL if it's shorter */
    if (len < sizeof(addr->call))
        for (unsigned i = 0; i < sizeof(addr->call) - len; i++)
            ax25_putchar(ctx, ' ' << 1);
}

void ax25_send(AX25Ctx *ctx, const AX25Call *dst, const AX25Call *src, const void *_buf, size_t len)
{
    const uint8_t *buf = (const uint8_t *)_buf;

    ctx->crc_out = CRC_CCITT_INIT_VAL;
    kfile_putc(HDLC_FLAG, ctx->ch);

    ax25_sendCall(ctx, dst);
    ax25_putchar(ctx, dst->ssid << 1);

    ax25_sendCall(ctx, src);
    ax25_putchar(ctx, (src->ssid << 1) | 0x01);
    ax25_putchar(ctx, AX25_CTRL_UI);
    ax25_putchar(ctx, AX25_PID_NOLAYER3);

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

    /*
     * According to AX25 protocol,
     * CRC is sent in reverse order!
     */
    uint8_t crcl = (ctx->crc_out & 0xff) ^ 0xff;
    uint8_t crch = (ctx->crc_out >> 8) ^ 0xff;
    ax25_putchar(ctx, crcl);
    ax25_putchar(ctx, crch);

    ASSERT(ctx->crc_out == AX25_CRC_CORRECT);

    kfile_putc(HDLC_FLAG, ctx->ch);
}


void ax25_init(AX25Ctx *ctx, KFile *channel, ax25_callback_t hook)
{
    ASSERT(ctx);
    ASSERT(channel);

    memset(ctx, 0, sizeof(*ctx));
    ctx->ch = channel;
    ctx->hook = hook;
    ctx->crc_in = ctx->crc_out = CRC_CCITT_INIT_VAL;
}