--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/trau-parse.c	Fri May 24 07:17:23 2024 +0000
@@ -0,0 +1,213 @@
+/*
+ * This program reads a 64 kbit/s timeslot recording file, examines one
+ * of the four 16 kbit/s subslots (selected), looks for GSM 08.60 TRAU
+ * frames, and dumps whatever it finds.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+
+static unsigned file_offset;
+
+static enum {
+	HUNT_FOR_0,
+	HUNT_FOUND_0,
+	GOT_8_ZEROS,
+	SYNCED
+} state;
+static unsigned hunt_for_0_count, frame_pos_count;
+static uint8_t in_frame_2bit[160], frame_bits[320];
+
+static void
+unpack_dibits()
+{
+	int i, inb;
+	uint8_t *op;
+
+	op = frame_bits;
+	for (i = 0; i < 160; i++) {
+		inb = in_frame_2bit[i];
+		if (inb & 2)
+			*op++ = 1;
+		else
+			*op++ = 0;
+		if (inb & 1)
+			*op++ = 1;
+		else
+			*op++ = 0;
+	}
+}
+
+static unsigned
+bits_to_num(bits, nbits)
+	uint8_t *bits;
+	unsigned nbits;
+{
+	unsigned accum;
+	unsigned n;
+
+	accum = 0;
+	for (n = 0; n < nbits; n++) {
+		accum <<= 1;
+		if (*bits)
+			accum |= 1;
+		bits++;
+	}
+	return accum;
+}
+
+static void
+process_frame()
+{
+	unsigned c1_5, c6_11;
+
+	printf("Frame at 0x%x:\n", file_offset - 160);
+	printf("  C1-C5: %u%u%u%u%u", frame_bits[17], frame_bits[18],
+		frame_bits[19], frame_bits[20], frame_bits[21]);
+	c1_5 = bits_to_num(frame_bits + 17);
+	switch (c1_5) {
+	case 0x02:
+		fputs(" (FR UL)", stdout);
+		break;
+	case 0x1C:
+		fputs(" (FR DL)", stdout);
+		break;
+	case 0x1E:
+		fputs(" (EFR)", stdout);
+		break;
+	case 0x10:
+		fputs(" (idle UL)", stdout);
+		break;
+	case 0x0E:
+		fputs(" (idle DL)", stdout);
+		break;
+	}
+	putchar('\n');
+	c6_11 = bits_to_num(frame_bits + 22);
+	printf("  C6-C11: %u\n", c6_11);
+	printf("  C12=%u C13=%u C14=%u C15=%u\n", frame_bits[28],
+		frame_bits[29], frame_bits[30], frame_bits[31]);
+	/* payload to be handled */
+	printf("  C16=%u C17=%u C18=%u C19=%u C20=%u C21=%u\n",
+		frame_bits[310], frame_bits[311], frame_bits[312],
+		frame_bits[313], frame_bits[314], frame_bits[315]);
+	printf("  T1=%u T2=%u T3=%u T4=%u\n", frame_bits[316], frame_bits[317],
+		frame_bits[318], frame_bits[319]);
+}
+
+static int
+check_sync_zeros()
+{
+	int i;
+
+	for (i = 0; i < 16; i++) {
+		if (frame_bits[i])
+			return 0;
+	}
+	return 1;
+}
+
+static int
+check_sync_ones()
+{
+	int i;
+
+	for (i = 1; i < 20; i++) {
+		if (!frame_bits[i*16])
+			return 0;
+	}
+	return 1;
+}
+
+static void
+check_sync()
+{
+	if (check_sync_zeros() && check_sync_ones())
+		return;
+	printf("Bad frame sync, returning to hunt state\n");
+	state = HUNT_FOR_0;
+}
+
+static void
+byte_input(inb)
+{
+	switch (state) {
+	case HUNT_FOR_0:
+		if (inb != 0)
+			return;
+		state = HUNT_FOUND_0;
+		hunt_for_0_count = 1;
+		return;
+	case HUNT_FOUND_0:
+		if (inb != 0) {
+			state = HUNT_FOR_0;
+			return;
+		}
+		hunt_for_0_count++;
+		if (hunt_for_0_count >= 8)
+			state = GOT_8_ZEROS;
+		return;
+	case GOT_8_ZEROS:
+		if (inb & 2) {
+			printf("Found frame sync at file offset 0x%x\n",
+				file_offset - 8);
+			bzero(in_frame_2bit, 8);
+			in_frame_2bit[8] = inb;
+			frame_pos_count = 9;
+			state = SYNCED;
+			return;
+		}
+		if (inb != 0)
+			state = HUNT_FOR_0;
+		return;
+	case SYNCED:
+		in_frame_2bit[frame_pos_count++] = inb;
+		if (frame_pos_count < 160)
+			return;
+		frame_pos_count = 0;
+		unpack_dibits();
+		process_frame();
+		check_sync();
+		return;
+	default:
+		fprintf(stderr, "BUG: bad sync state\n");
+		abort();
+	}
+}
+
+main(argc, argv)
+	char **argv;
+{
+	FILE *inf;
+	int subslot, right_shift;
+	int inb;
+
+	if (argc != 3) {
+		fprintf(stderr, "usage: %s binfile subslot\n", argv[0]);
+		exit(1);
+	}
+	inf = fopen(argv[1], "r");
+	if (!inf) {
+		perror(argv[1]);
+		exit(1);
+	}
+	subslot = atoi(argv[2]);
+	if (subslot < 0 || subslot > 3) {
+		fprintf(stderr, "error: invalid subslot argument\n");
+		exit(1);
+	}
+	right_shift = (3 - subslot) * 2;
+	state = HUNT_FOR_0;
+	for (file_offset = 0; ; file_offset++) {
+		inb = getc(inf);
+		if (inb < 0)
+			break;
+		inb >>= right_shift;
+		inb &= 3;
+		byte_input(inb);
+	}
+	exit(0);
+}