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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.
37 * \author Francesco Sacchi <batt@develer.com>
42 #include "cfg/cfg_ax25.h"
44 #include <algo/crc_ccitt.h>
46 #define LOG_LEVEL AX25_LOG_LEVEL
47 #define LOG_FORMAT AX25_LOG_FORMAT
50 #include <string.h> //memset, memcmp
51 #include <ctype.h> //isalnum, toupper
53 #if CONFIG_AX25_RPT_LST
54 #define AX25_SET_REPEATED(msg, idx, val) \
58 (msg)->rpt_flags |= BV(idx) ; \
60 (msg)->rpt_flags &= ~BV(idx) ; \
64 #define DECODE_CALL(buf, addr) \
65 for (unsigned i = 0; i < sizeof((addr)); i++) \
67 char c = (*(buf)++ >> 1); \
68 (addr)[i] = (c == ' ') ? '\x0' : c; \
71 static void ax25_decode(AX25Ctx *ctx)
74 uint8_t *buf = ctx->buf;
76 DECODE_CALL(buf, msg.dst.call);
77 msg.dst.ssid = (*buf++ >> 1) & 0x0F;
79 DECODE_CALL(buf, msg.src.call);
80 msg.src.ssid = (*buf >> 1) & 0x0F;
82 LOG_INFO("SRC[%.6s-%d], DST[%.6s-%d]\n", msg.src.call, msg.src.ssid, msg.dst.call, msg.dst.ssid);
84 /* Repeater addresses */
85 #if CONFIG_AX25_RPT_LST
86 for (msg.rpt_cnt = 0; !(*buf++ & 0x01) && (msg.rpt_cnt < countof(msg.rpt_lst)); msg.rpt_cnt++)
88 DECODE_CALL(buf, msg.rpt_lst[msg.rpt_cnt].call);
89 msg.rpt_lst[msg.rpt_cnt].ssid = (*buf >> 1) & 0x0F;
90 AX25_SET_REPEATED(&msg, msg.rpt_cnt, (*buf & 0x80));
92 LOG_INFO("RPT%d[%.6s-%d]%c\n", msg.rpt_cnt,
93 msg.rpt_lst[msg.rpt_cnt].call,
94 msg.rpt_lst[msg.rpt_cnt].ssid,
95 (AX25_REPEATED(&msg, msg.rpt_cnt) ? '*' : ' '));
98 while (!(*buf++ & 0x01))
102 DECODE_CALL(buf, rpt);
103 ssid = (*buf >> 1) & 0x0F;
104 LOG_INFO("RPT[%.6s-%d]\n", rpt, ssid);
109 if (msg.ctrl != AX25_CTRL_UI)
111 LOG_WARN("Only UI frames are handled, got [%02X]\n", msg.ctrl);
116 if (msg.pid != AX25_PID_NOLAYER3)
118 LOG_WARN("Only frames without layer3 protocol are handled, got [%02X]\n", msg.pid);
122 msg.len = ctx->frm_len - 2 - (buf - ctx->buf);
124 LOG_INFO("DATA: %.*s\n", msg.len, msg.info);
132 * Check if there are any AX25 messages to be processed.
133 * This function read available characters from the medium and search for
135 * If a message is found it is decoded and the linked callback executed.
136 * This function may be blocking if there are no available chars and the KFile
137 * used in \a ctx to access the medium is configured in blocking mode.
139 * \param ctx AX25 context to operate on.
141 void ax25_poll(AX25Ctx *ctx)
145 while ((c = kfile_getc(ctx->ch)) != EOF)
147 if (!ctx->escape && c == HDLC_FLAG)
149 if (ctx->frm_len >= AX25_MIN_FRAME_LEN)
151 if (ctx->crc_in == AX25_CRC_CORRECT)
153 LOG_INFO("Frame found!\n");
158 LOG_INFO("CRC error, computed [%04X]\n", ctx->crc_in);
162 ctx->crc_in = CRC_CCITT_INIT_VAL;
167 if (!ctx->escape && c == HDLC_RESET)
169 LOG_INFO("HDLC reset\n");
174 if (!ctx->escape && c == AX25_ESC)
182 if (ctx->frm_len < CONFIG_AX25_FRAME_BUF_LEN)
184 ctx->buf[ctx->frm_len++] = c;
185 ctx->crc_in = updcrc_ccitt(c, ctx->crc_in);
189 LOG_INFO("Buffer overrun");
196 if (kfile_error(ctx->ch))
198 LOG_ERR("Channel error [%04x]\n", kfile_error(ctx->ch));
199 kfile_clearerr(ctx->ch);
203 static void ax25_putchar(AX25Ctx *ctx, uint8_t c)
205 if (c == HDLC_FLAG || c == HDLC_RESET
207 kfile_putc(AX25_ESC, ctx->ch);
208 ctx->crc_out = updcrc_ccitt(c, ctx->crc_out);
209 kfile_putc(c, ctx->ch);
212 static void ax25_sendCall(AX25Ctx *ctx, const AX25Call *addr, bool last)
214 unsigned len = MIN(sizeof(addr->call), strlen(addr->call));
216 for (unsigned i = 0; i < len; i++)
218 uint8_t c = addr->call[i];
219 ASSERT(isalnum(c) || c == ' ');
221 ax25_putchar(ctx, c << 1);
224 /* Fill with spaces the rest of the CALL if it's shorter */
225 if (len < sizeof(addr->call))
226 for (unsigned i = 0; i < sizeof(addr->call) - len; i++)
227 ax25_putchar(ctx, ' ' << 1);
229 /* The bit7 "has-been-repeated" flag is not implemented here */
230 /* Bits6:5 should be set to 1 for all SSIDs (0x60) */
231 /* The bit0 of last call SSID should be set to 1 */
232 uint8_t ssid = 0x60 | (addr->ssid << 1) | (last ? 0x01 : 0);
233 ax25_putchar(ctx, ssid);
237 * Send an AX25 frame on the channel through a specific path.
238 * \param ctx AX25 context to operate on.
239 * \param path An array of callsigns used as path, \see AX25_PATH for
240 * an handy way to create a path.
241 * \param path_len callsigns path lenght.
242 * \param _buf payload buffer.
243 * \param len length of the payload.
245 void ax25_sendVia(AX25Ctx *ctx, const AX25Call *path, size_t path_len, const void *_buf, size_t len)
247 const uint8_t *buf = (const uint8_t *)_buf;
249 ASSERT(path_len >= 2);
251 ctx->crc_out = CRC_CCITT_INIT_VAL;
252 kfile_putc(HDLC_FLAG, ctx->ch);
256 for (size_t i = 0; i < path_len; i++)
257 ax25_sendCall(ctx, &path[i], (i == path_len - 1));
259 ax25_putchar(ctx, AX25_CTRL_UI);
260 ax25_putchar(ctx, AX25_PID_NOLAYER3);
263 ax25_putchar(ctx, *buf++);
266 * According to AX25 protocol,
267 * CRC is sent in reverse order!
269 uint8_t crcl = (ctx->crc_out & 0xff) ^ 0xff;
270 uint8_t crch = (ctx->crc_out >> 8) ^ 0xff;
271 ax25_putchar(ctx, crcl);
272 ax25_putchar(ctx, crch);
274 ASSERT(ctx->crc_out == AX25_CRC_CORRECT);
276 kfile_putc(HDLC_FLAG, ctx->ch);
279 static void print_call(KFile *ch, const AX25Call *call)
281 kfile_printf(ch, "%.6s", call->call);
283 kfile_printf(ch, "-%d", call->ssid);
287 * Print a AX25 message in TNC-2 packet monitor format.
288 * \param ch a kfile channel where the message will be printed.
289 * \param msg the message to be printed.
291 void ax25_print(KFile *ch, const AX25Msg *msg)
293 print_call(ch, &msg->src);
295 print_call(ch, &msg->dst);
297 #if CONFIG_AX25_RPT_LST
298 for (int i = 0; i < msg->rpt_cnt; i++)
301 print_call(ch, &msg->rpt_lst[i]);
302 /* Print a '*' if packet has already been transmitted
303 * by this repeater */
304 if (AX25_REPEATED(msg, i))
309 kfile_printf(ch, ":%.*s\n", msg->len, msg->info);
314 * Init the AX25 protocol decoder.
316 * \param ctx AX25 context to init.
317 * \param channel Used to gain access to the physical medium
318 * \param hook Callback function called when a message is received
320 void ax25_init(AX25Ctx *ctx, KFile *channel, ax25_callback_t hook)
325 memset(ctx, 0, sizeof(*ctx));
328 ctx->crc_in = ctx->crc_out = CRC_CCITT_INIT_VAL;