implement APRS display mode for iGates

run with "multimonNG -A" to get APRS format output.

Example output:

	APRS: DO1GL-5>APDR12,DO1GL*,WIDE2-2:=5111.11N/01111.11E$ http://aprsdroid.org/

hdlc.c

@@ -79,6 +79,64 @@ static inline int check_crc_ccitt(const unsigned char *buf, int cnt)
 
 /* ---------------------------------------------------------------------- */
 
+int aprs_mode = 0;
+
+static void aprs_print_ax25call(unsigned char *call, int is_repeater)
+{
+	int i;
+	for (i = 0; i < 6; i++)
+		if ((call[i] &0xfe) != 0x40)
+			verbprintf(0, "%c",call[i] >> 1);
+	int ssid = (call[6] >> 1) & 0xf;
+	if (ssid)
+		verbprintf(0, "-%u",ssid);
+	// hack: only display "*" on the last repeater, as opposed to all that already repeated
+	if (is_repeater && (call[6] & 0x80))
+			verbprintf(0, "*");
+}
+static void aprs_disp_packet(unsigned char *bp, unsigned int len)
+{
+	unsigned char *hdr = bp + 14;
+	unsigned int hlen = len - 14;
+	// skip address fields
+	while ((!(hdr[-1] & 1)) && (hlen >= 7)) {
+		hdr += 7;
+		hlen -= 7;
+	}
+	if (*hdr++ != 0x03) // Ctrl 0x03 = UI frame
+		return;
+	if (*hdr++ != 0xf0) // PID 0xf0 = no layer 3 protocol
+		return;
+
+	verbprintf(0, "APRS: ");
+	// source call
+	aprs_print_ax25call(&bp[7], 0);
+	verbprintf(0, ">");
+	// tocall
+	aprs_print_ax25call(&bp[0], 0);
+	bp += 14;
+	len -= 14;
+	// via callsigns
+	while ((!(bp[-1] & 1)) && (len >= 7)) {
+		if ((!(bp[-1] & 1)) && (len >= 7))
+			verbprintf(0, ",");
+		aprs_print_ax25call(&bp[0], 1);
+		bp += 7;
+		len -= 7;
+	}
+	verbprintf(0, ":");
+	// end of header
+	bp += 2;
+	len -= 2;
+	if(!len)
+		return;
+	while (len) {
+		verbprintf(0, "%c",*bp++);
+		len--;
+	}
+	verbprintf(0, "\n");
+}
+
 static void ax25_disp_packet(struct demod_state *s, unsigned char *bp, unsigned int len)
 {
         unsigned char v1=1,cmd=0;
@@ -125,6 +183,10 @@ static void ax25_disp_packet(struct demod_state *s, unsigned char *bp, unsigned
                  */
                 if (len < 15) 
 			return;
+		if (aprs_mode) {
+			aprs_disp_packet(bp, len);
+			return;
+		}
                 if ((bp[6] & 0x80) != (bp[13] & 0x80)) {
                         v1 = 0;
                         cmd = (bp[6] & 0x80);

unixinput.c

@@ -78,6 +78,7 @@ static unsigned int dem_mask[(NUMDEMOD+31)/32];
 
 static int verbose_level = 0;
 extern int pocsag_mode;
+extern int aprs_mode;
 void quit(void);
 
 /* ---------------------------------------------------------------------- */
@@ -489,6 +490,7 @@ static const char usage_str[] = "multimonNG\n"
         "  -v <level> : level of verbosity (for example '-v 10')\n"
         "  -f <mode>  : forces POCSAG data decoding as <mode> (<mode> can be 'numeric', 'alpha' and 'skyper')\n"
         "  -h         : this help\n"
+        "  -A         : APRS mode (TNC2 text output)\n"
         "   Raw input requires one channel, 16 bit, signed integer (platform-native)\n"
         "   samples at the demodulator's input sampling rate, which is\n"
         "   usually 22050 kHz. Raw input is assumed and required if piped input is used.\n";
@@ -511,7 +513,7 @@ int main(int argc, char *argv[])
     for (i = 0; i < NUMDEMOD; i++)
         fprintf(stderr, " %s", dem[i]->name);
     fprintf(stderr, "\n");
-    while ((c = getopt(argc, argv, "t:a:s:v:f:cqh")) != EOF) {
+    while ((c = getopt(argc, argv, "t:a:s:v:f:cqhA")) != EOF) {
         switch (c) {
         case 'h':
         case '?':
@@ -522,6 +524,17 @@ int main(int argc, char *argv[])
             quietflg++;
             break;
 
+        case 'A':
+            aprs_mode = 1;
+	    memset(dem_mask, 0, sizeof(dem_mask));
+            mask_first = 0;
+            for (i = 0; i < NUMDEMOD; i++)
+                if (!strcasecmp("AFSK1200", dem[i]->name)) {
+                    MASK_SET(i);
+                    break;
+                }
+            break;
+
         case 'v':
             verbose_level = strtoul(optarg, 0, 0);
             break;