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29 * Copyright 2009 Develer S.r.l. (http://www.develer.com/)
32 * \brief Simple AX25 data link layer implementation.
34 * For now, only UI frames without any Layer 3 protocol are handled.
35 * This however is enough to send/receive APRS packets.
38 * \author Francesco Sacchi <batt@develer.com>
43 #include "cfg/cfg_ax25.h"
45 #include <algo/crc_ccitt.h>
47 #define LOG_LEVEL AX25_LOG_LEVEL
48 #define LOG_FORMAT AX25_LOG_FORMAT
51 #include <string.h> //memset, memcmp
52 #include <ctype.h> //isalnum, toupper
54 #define DECODE_CALL(buf, addr) \
55 for (unsigned i = 0; i < sizeof((addr)); i++) \
57 char c = (*(buf)++ >> 1); \
58 (addr)[i] = (c == ' ') ? '\x0' : c; \
61 static void ax25_decode(AX25Ctx *ctx)
64 uint8_t *buf = ctx->buf;
66 DECODE_CALL(buf, msg.dst.call);
67 msg.dst.ssid = (*buf++ >> 1) & 0x0F;
69 DECODE_CALL(buf, msg.src.call);
70 msg.src.ssid = (*buf >> 1) & 0x0F;
72 LOG_INFO("SRC[%.6s-%d], DST[%.6s-%d]\n", msg.src.call, msg.src.ssid, msg.dst.call, msg.dst.ssid);
74 /* Repeater addresses */
75 #if CONFIG_AX25_RPT_LST
76 for (msg.rpt_cnt = 0; !(*buf++ & 0x01) && (msg.rpt_cnt < countof(msg.rpt_lst)); msg.rpt_cnt++)
78 DECODE_CALL(buf, msg.rpt_lst[msg.rpt_cnt].call);
79 msg.rpt_lst[msg.rpt_cnt].ssid = (*buf >> 1) & 0x0F;
80 LOG_INFO("RPT%d[%.6s-%d]\n", msg.rpt_cnt, msg.rpt_lst[msg.rpt_cnt].call, msg.rpt_lst[msg.rpt_cnt].ssid);
83 while (!(*buf++ & 0x01))
87 DECODE_CALL(buf, rpt);
88 ssid = (*buf >> 1) & 0x0F;
89 LOG_INFO("RPT[%.6s-%d]\n", rpt, ssid);
94 if (msg.ctrl != AX25_CTRL_UI)
96 LOG_WARN("Only UI frames are handled, got [%02X]\n", msg.ctrl);
101 if (msg.pid != AX25_PID_NOLAYER3)
103 LOG_WARN("Only frames without layer3 protocol are handled, got [%02X]\n", msg.pid);
107 msg.len = ctx->frm_len - 2 - (buf - ctx->buf);
109 LOG_INFO("DATA: %.*s\n", msg.len, msg.info);
117 * Check if there are any AX25 messages to be processed.
118 * This function read available characters from the medium and search for
120 * If a message is found it is decoded and the linked callback executed.
121 * This function may be blocking if there are no available chars and the KFile
122 * used in \a ctx to access the medium is configured in blocking mode.
124 * \param ctx AX25 context to operate on.
126 void ax25_poll(AX25Ctx *ctx)
130 while ((c = kfile_getc(ctx->ch)) != EOF)
132 if (!ctx->escape && c == HDLC_FLAG)
134 if (ctx->frm_len >= AX25_MIN_FRAME_LEN)
136 if (ctx->crc_in == AX25_CRC_CORRECT)
138 LOG_INFO("Frame found!\n");
143 LOG_INFO("CRC error, computed [%04X]\n", ctx->crc_in);
147 ctx->crc_in = CRC_CCITT_INIT_VAL;
152 if (!ctx->escape && c == HDLC_RESET)
154 LOG_INFO("HDLC reset\n");
159 if (!ctx->escape && c == AX25_ESC)
167 if (ctx->frm_len < CONFIG_AX25_FRAME_BUF_LEN)
169 ctx->buf[ctx->frm_len++] = c;
170 ctx->crc_in = updcrc_ccitt(c, ctx->crc_in);
174 LOG_INFO("Buffer overrun");
181 if (kfile_error(ctx->ch))
183 LOG_ERR("Channel error [%04x]\n", kfile_error(ctx->ch));
184 kfile_clearerr(ctx->ch);
188 static void ax25_putchar(AX25Ctx *ctx, uint8_t c)
190 if (c == HDLC_FLAG || c == HDLC_RESET
192 kfile_putc(AX25_ESC, ctx->ch);
193 ctx->crc_out = updcrc_ccitt(c, ctx->crc_out);
194 kfile_putc(c, ctx->ch);
197 static void ax25_sendCall(AX25Ctx *ctx, const AX25Call *addr, bool last)
199 unsigned len = MIN(sizeof(addr->call), strlen(addr->call));
201 for (unsigned i = 0; i < len; i++)
203 uint8_t c = addr->call[i];
204 ASSERT(isalnum(c) || c == ' ');
206 ax25_putchar(ctx, c << 1);
209 /* Fill with spaces the rest of the CALL if it's shorter */
210 if (len < sizeof(addr->call))
211 for (unsigned i = 0; i < sizeof(addr->call) - len; i++)
212 ax25_putchar(ctx, ' ' << 1);
214 /* The bit0 of last call SSID should be set to 1 */
215 uint8_t ssid = addr->ssid << 1 | (last ? 0x01 : 0);
216 ax25_putchar(ctx, ssid);
220 * Send an AX25 frame on the channel through a specific path.
221 * \param ctx AX25 context to operate on.
222 * \param path An array of callsigns used as path, \see AX25_PATH for
223 * an handy way to create a path.
224 * \param path_len callsigns path lenght.
225 * \param _buf payload buffer.
226 * \param len length of the payload.
228 void ax25_sendVia(AX25Ctx *ctx, const AX25Call *path, size_t path_len, const void *_buf, size_t len)
230 const uint8_t *buf = (const uint8_t *)_buf;
232 ASSERT(path_len >= 2);
234 ctx->crc_out = CRC_CCITT_INIT_VAL;
235 kfile_putc(HDLC_FLAG, ctx->ch);
239 for (size_t i = 0; i < path_len; i++)
240 ax25_sendCall(ctx, &path[i], (i == path_len - 1));
242 ax25_putchar(ctx, AX25_CTRL_UI);
243 ax25_putchar(ctx, AX25_PID_NOLAYER3);
246 ax25_putchar(ctx, *buf++);
249 * According to AX25 protocol,
250 * CRC is sent in reverse order!
252 uint8_t crcl = (ctx->crc_out & 0xff) ^ 0xff;
253 uint8_t crch = (ctx->crc_out >> 8) ^ 0xff;
254 ax25_putchar(ctx, crcl);
255 ax25_putchar(ctx, crch);
257 ASSERT(ctx->crc_out == AX25_CRC_CORRECT);
259 kfile_putc(HDLC_FLAG, ctx->ch);
262 static void print_call(KFile *ch, const AX25Call *call)
264 kfile_printf(ch, "%.6s", call->call);
266 kfile_printf(ch, "-%d", call->ssid);
270 * Print a AX25 message in TNC-2 packet monitor format.
271 * \param ch a kfile channel where the message will be printed.
272 * \param msg the message to be printed.
274 void ax25_print(KFile *ch, const AX25Msg *msg)
276 print_call(ch, &msg->src);
278 print_call(ch, &msg->dst);
280 #if CONFIG_AX25_RPT_LST
281 for (int i = 0; i < msg->rpt_cnt; i++)
284 print_call(ch, &msg->rpt_lst[i]);
285 // TODO: add * to the trasmitting digi
289 kfile_printf(ch, ":%.*s\n", msg->len, msg->info);
294 * Init the AX25 protocol decoder.
296 * \param ctx AX25 context to init.
297 * \param channel Used to gain access to the physical medium
298 * \param hook Callback function called when a message is received
300 void ax25_init(AX25Ctx *ctx, KFile *channel, ax25_callback_t hook)
305 memset(ctx, 0, sizeof(*ctx));
308 ctx->crc_in = ctx->crc_out = CRC_CCITT_INIT_VAL;