ax25.c

Go to the documentation of this file.

#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

#if CONFIG_AX25_RPT_LST
    #define AX25_SET_REPEATED(msg, idx, val) \
        do \
        { \
            if (val) \
                (msg)->rpt_flags |= BV(idx) ; \
            else \
                (msg)->rpt_flags &= ~BV(idx) ; \
        } while(0) 
#endif

#define DECODE_CALL(buf, addr) \
    for (unsigned i = 0; i < sizeof((addr)); i++) \
    { \
        char c = (*(buf)++ >> 1); \
        (addr)[i] = (c == ' ') ? '\x0' : c; \
    }

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;
            AX25_SET_REPEATED(&msg, msg.rpt_cnt, (*buf & 0x80));

            LOG_INFO("RPT%d[%.6s-%d]%c\n", msg.rpt_cnt, 
                msg.rpt_lst[msg.rpt_cnt].call, 
                msg.rpt_lst[msg.rpt_cnt].ssid,
                (AX25_REPEATED(&msg, msg.rpt_cnt) ? '*' : ' '));
        }
    #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, bool last)
{
    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);

    /* The bit7 "has-been-repeated" flag is not implemented here */
    /* Bits6:5 should be set to 1 for all SSIDs (0x60) */
    /* The bit0 of last call SSID should be set to 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;
    ASSERT(path);
    ASSERT(path_len >= 2);

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


    /* Send call */
    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++);

    /*
     * 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);
}

static void print_call(KFile *ch, const AX25Call *call)
{
    kfile_printf(ch, "%.6s", call->call);
    if (call->ssid)
        kfile_printf(ch, "-%d", call->ssid);
}

void ax25_print(KFile *ch, const AX25Msg *msg)
{
    print_call(ch, &msg->src);
    kfile_putc('>', ch);
    print_call(ch, &msg->dst);

    #if CONFIG_AX25_RPT_LST
    for (int i = 0; i < msg->rpt_cnt; i++)
    {
        kfile_putc(',', ch);
        print_call(ch, &msg->rpt_lst[i]);
        /* Print a '*' if packet has already been transmitted 
         * by this repeater */
        if (AX25_REPEATED(msg, i))
            kfile_putc('*', ch);
    }
    #endif

    kfile_printf(ch, ":%.*s\n", msg->len, msg->info);
}


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;
}