Parse full airspy input.

adsbus.c

@@ -131,7 +131,7 @@ static int loop(int bfd) {
 				while (airspy_adsb_parse(&buf, &packet)) {
 				}
 
-				if (buf.length == BUF_LEN) {
+				if (buf.length == BUF_LEN_MAX) {
 					fprintf(stderr, "Input buffer overrun. This probably means that adsbus doesn't understand the protocol that this source is speaking.\n");
 					return -1;
 				}
@@ -142,6 +142,8 @@ static int loop(int bfd) {
 
 
 int main(int argc, char *argv[]) {
+	hex_init();
+
 	struct opts opts = {
 		.backend_node = "localhost",
 		.backend_service = "30006",

airspy_adsb.c

@@ -1,27 +1,53 @@
+#include <stdbool.h>
 #include <stdio.h>
 #include <string.h>
 
 #include "common.h"
 #include "airspy_adsb.h"
 
+static bool airspy_adsb_parse_common(char *, struct packet *);
+
+
 bool airspy_adsb_parse(struct buf *buf, struct packet *packet) {
 	if (buf->length < 35 ||
 	    buf_chr(buf, 0) != '*') {
 		return false;
 	}
 	if (buf->length >= 35 &&
+	    buf_chr(buf, 33) == '\r' &&
 	    buf_chr(buf, 34) == '\n' &&
 			buf_chr(buf, 15) == ';') {
+		if (!airspy_adsb_parse_common(buf_at(buf, 16), packet)) {
+			return false;
+		}
 		packet->type = MODE_S_SHORT;
+		hex_to_bin(packet->data, buf_at(buf, 1), 7);
 		buf_consume(buf, 35);
 		return true;
 	}
 	if (buf->length >= 49 &&
+	    buf_chr(buf, 47) == '\r' &&
 	    buf_chr(buf, 48) == '\n' &&
 			buf_chr(buf, 29) == ';') {
+		if (!airspy_adsb_parse_common(buf_at(buf, 30), packet)) {
+			return false;
+		}
 		packet->type = MODE_S_LONG;
+		hex_to_bin(packet->data, buf_at(buf, 1), 14);
 		buf_consume(buf, 49);
 		return true;
 	}
 	return false;
 }
+
+static bool airspy_adsb_parse_common(char *in, struct packet *packet) {
+	if (in[8] != ';' ||
+	    in[11] != ';' ||
+			in[16] != ';') {
+		return false;
+	}
+	uint16_t mlat_mhz = 2 * hex_to_int(&in[9], 1);
+	packet->mlat_timestamp = hex_to_int(in, 4) * (MLAT_MHZ / mlat_mhz);
+	packet->rssi = hex_to_int(&in[12], 2) * (RSSI_MAX / (1 << 16));
+	return true;
+}

common.c

@@ -8,13 +8,13 @@
 
 
 ssize_t buf_fill(struct buf *buf, int fd) {
-	if (buf->start + buf->length == BUF_LEN) {
+	if (buf->start + buf->length == BUF_LEN_MAX) {
 		assert(buf->start > 0);
 		memmove(buf->buf, buf_at(buf, 0), buf->length);
 		buf->start = 0;
 	}
 
-	size_t space = BUF_LEN - buf->length - buf->start;
+	size_t space = BUF_LEN_MAX - buf->length - buf->start;
 	ssize_t in = read(fd, buf_at(buf, buf->length), space);
 	if (in < 0) {
 		return in;
@@ -33,3 +33,36 @@ void buf_consume(struct buf *buf, size_t length) {
 		buf->start = 0;
 	}
 }
+
+
+static uint8_t hex_table[256] = {0};
+
+void hex_init() {
+	for (int i = '0'; i <= '9'; i++) {
+		hex_table[i] = i - '0';
+	}
+	for (int i = 'a'; i <= 'f'; i++) {
+		hex_table[i] = 10 + i - 'a';
+	}
+	for (int i = 'A'; i <= 'F'; i++) {
+		hex_table[i] = 10 + i - 'A';
+	}
+}
+
+void hex_to_bin(char *out, char *in, size_t bytes) {
+	uint8_t *in2 = (uint8_t *) in;
+	for (size_t i = 0, j = 0; i < bytes; i++, j += 2) {
+		out[i] = (hex_table[in2[j]] << 4) | hex_table[in2[j + 1]];
+	}
+}
+
+uint64_t hex_to_int(char *in, size_t bytes) {
+	uint8_t *in2 = (uint8_t *) in;
+	uint64_t ret = 0;
+	bytes *= 2;
+	for (size_t i = 0; i < bytes; i++) {
+		ret <<= 4;
+		ret |= hex_table[in2[i]];
+	}
+	return ret;
+}

common.h

@@ -4,9 +4,9 @@
 
 //////// buf
 
-#define BUF_LEN 4096
+#define BUF_LEN_MAX 256
 struct buf {
-	char buf[BUF_LEN];
+	char buf[BUF_LEN_MAX];
 	size_t start;
 	size_t length;
 };
@@ -20,18 +20,22 @@ void buf_consume(struct buf *, size_t);
 
 //////// packet
 
-#define MLAT_HZ 60000000
-#define DATA_MAX 14
+#define MLAT_MHZ 120
+#define RSSI_MAX UINT32_MAX
+#define DATA_LEN_MAX 14
 struct packet {
 	enum {
 		MODE_AC,
 		MODE_S_SHORT,
 		MODE_S_LONG,
 	} type;
-	char data[DATA_MAX];
+	char data[DATA_LEN_MAX];
 	uint64_t mlat_timestamp;
 	uint32_t rssi;
 };
 
 
 //////// hex
+void hex_init();
+void hex_to_bin(char *, char *, size_t);
+uint64_t hex_to_int(char *, size_t);