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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 #define DECODE_CALL(buf, addr) \
54 for (unsigned i = 0; i < sizeof((addr)); i++) \
56 char c = (*(buf)++ >> 1); \
57 (addr)[i] = (c == ' ') ? '\x0' : c; \
60 static void ax25_decode(AX25Ctx *ctx)
63 uint8_t *buf = ctx->buf;
65 DECODE_CALL(buf, msg.dst.call);
66 msg.dst.ssid = (*buf++ >> 1) & 0x0F;
68 DECODE_CALL(buf, msg.src.call);
69 msg.src.ssid = (*buf >> 1) & 0x0F;
71 LOG_INFO("SRC[%.6s-%d], DST[%.6s-%d]\n", msg.src.call, msg.src.ssid, msg.dst.call, msg.dst.ssid);
73 /* Repeater addresses */
74 #if CONFIG_AX25_RPT_LST
75 for (msg.rpt_cnt = 0; !(*buf++ & 0x01) && (msg.rpt_cnt < countof(msg.rpt_lst)); msg.rpt_cnt++)
77 DECODE_CALL(buf, msg.rpt_lst[msg.rpt_cnt].call);
78 msg.rpt_lst[msg.rpt_cnt].ssid = (*buf >> 1) & 0x0F;
79 LOG_INFO("RPT%d[%.6s-%d]\n", msg.rpt_cnt, msg.rpt_lst[msg.rpt_cnt].call, msg.rpt_lst[msg.rpt_cnt].ssid);
82 while (!(*buf++ & 0x01))
86 DECODE_CALL(buf, rpt);
87 ssid = (*buf >> 1) & 0x0F;
88 LOG_INFO("RPT[%.6s-%d]\n", rpt, ssid);
93 if (msg.ctrl != AX25_CTRL_UI)
95 LOG_WARN("Only UI frames are handled, got [%02X]\n", msg.ctrl);
100 if (msg.pid != AX25_PID_NOLAYER3)
102 LOG_WARN("Only frames without layer3 protocol are handled, got [%02X]\n", msg.pid);
106 msg.len = ctx->frm_len - 2 - (buf - ctx->buf);
108 LOG_INFO("DATA: %.*s\n", msg.len, msg.info);
116 * Check if there are any AX25 messages to be processed.
117 * This function read available characters from the medium and search for
119 * If a message is found it is decoded and the linked callback executed.
120 * This function may be blocking if there are no available chars and the KFile
121 * used in \a ctx to access the medium is configured in blocking mode.
123 * \param ctx AX25 context to operate on.
125 void ax25_poll(AX25Ctx *ctx)
129 while ((c = kfile_getc(ctx->ch)) != EOF)
131 if (!ctx->escape && c == HDLC_FLAG)
133 if (ctx->frm_len >= AX25_MIN_FRAME_LEN)
135 if (ctx->crc_in == AX25_CRC_CORRECT)
137 LOG_INFO("Frame found!\n");
142 LOG_INFO("CRC error, computed [%04X]\n", ctx->crc_in);
146 ctx->crc_in = CRC_CCITT_INIT_VAL;
151 if (!ctx->escape && c == HDLC_RESET)
153 LOG_INFO("HDLC reset\n");
158 if (!ctx->escape && c == AX25_ESC)
166 if (ctx->frm_len < CONFIG_AX25_FRAME_BUF_LEN)
168 ctx->buf[ctx->frm_len++] = c;
169 ctx->crc_in = updcrc_ccitt(c, ctx->crc_in);
173 LOG_INFO("Buffer overrun");
180 if (kfile_error(ctx->ch))
182 LOG_ERR("Channel error [%04x]\n", kfile_error(ctx->ch));
183 kfile_clearerr(ctx->ch);
187 static void ax25_putchar(AX25Ctx *ctx, uint8_t c)
189 if (c == HDLC_FLAG || c == HDLC_RESET
191 kfile_putc(AX25_ESC, ctx->ch);
192 ctx->crc_out = updcrc_ccitt(c, ctx->crc_out);
193 kfile_putc(c, ctx->ch);
196 static void ax25_sendCall(AX25Ctx *ctx, const AX25Call *addr, bool last)
198 unsigned len = MIN(sizeof(addr->call), strlen(addr->call));
200 for (unsigned i = 0; i < len; i++)
202 uint8_t c = addr->call[i];
203 ASSERT(isalnum(c) || c == ' ');
205 ax25_putchar(ctx, c << 1);
208 /* Fill with spaces the rest of the CALL if it's shorter */
209 if (len < sizeof(addr->call))
210 for (unsigned i = 0; i < sizeof(addr->call) - len; i++)
211 ax25_putchar(ctx, ' ' << 1);
213 /* The bit0 of last call SSID should be set to 1 */
214 uint8_t ssid = addr->ssid << 1 | (last ? 0x01 : 0);
215 ax25_putchar(ctx, ssid);
219 * Send an AX25 frame on the channel through a specific path.
220 * \param ctx AX25 context to operate on.
221 * \param path An array of callsigns used as path, \see AX25_PATH for
222 * an handy way to create a path.
223 * \param path_len callsigns path lenght.
224 * \param _buf payload buffer.
225 * \param len length of the payload.
227 void ax25_sendVia(AX25Ctx *ctx, const AX25Call *path, size_t path_len, const void *_buf, size_t len)
229 const uint8_t *buf = (const uint8_t *)_buf;
231 ASSERT(path_len >= 2);
233 ctx->crc_out = CRC_CCITT_INIT_VAL;
234 kfile_putc(HDLC_FLAG, ctx->ch);
238 for (size_t i = 0; i < path_len; i++)
239 ax25_sendCall(ctx, &path[i], (i == path_len - 1));
241 ax25_putchar(ctx, AX25_CTRL_UI);
242 ax25_putchar(ctx, AX25_PID_NOLAYER3);
245 ax25_putchar(ctx, *buf++);
248 * According to AX25 protocol,
249 * CRC is sent in reverse order!
251 uint8_t crcl = (ctx->crc_out & 0xff) ^ 0xff;
252 uint8_t crch = (ctx->crc_out >> 8) ^ 0xff;
253 ax25_putchar(ctx, crcl);
254 ax25_putchar(ctx, crch);
256 ASSERT(ctx->crc_out == AX25_CRC_CORRECT);
258 kfile_putc(HDLC_FLAG, ctx->ch);
261 static void print_call(KFile *ch, const AX25Call *call)
263 kfile_printf(ch, "%.6s", call->call);
265 kfile_printf(ch, "-%d", call->ssid);
269 * Print a AX25 message in TNC-2 packet monitor format.
270 * \param ch a kfile channel where the message will be printed.
271 * \param msg the message to be printed.
273 void ax25_print(KFile *ch, const AX25Msg *msg)
275 print_call(ch, &msg->src);
277 print_call(ch, &msg->dst);
279 #if CONFIG_AX25_RPT_LST
280 for (int i = 0; i < msg->rpt_cnt; i++)
283 print_call(ch, &msg->rpt_lst[i]);
284 // TODO: add * to the trasmitting digi
288 kfile_printf(ch, ":%.*s\n", msg->len, msg->info);
293 * Init the AX25 protocol decoder.
295 * \param ctx AX25 context to init.
296 * \param channel Used to gain access to the physical medium
297 * \param hook Callback function called when a message is received
299 void ax25_init(AX25Ctx *ctx, KFile *channel, ax25_callback_t hook)
304 memset(ctx, 0, sizeof(*ctx));
307 ctx->crc_in = ctx->crc_out = CRC_CCITT_INIT_VAL;