--- a/trau-decode/parse-amr.c	Sat Feb 08 06:22:45 2025 +0000
+++ b/trau-decode/parse-amr.c	Sat Feb 08 09:13:30 2025 +0000
@@ -1,6 +1,6 @@
 /*
- * This module contains a bit of code that has been factored out of
- * trau-parse program; it handles AMR frames.
+ * Here we implement parsing/decoding of AMR frames as in 3GPP TS 48.060
+ * section 5.5.1.2, striving to decode and display as much as we can.
  */
 
 #include <stdio.h>
@@ -8,10 +8,34 @@
 #include <stdlib.h>
 #include <string.h>
 #include <strings.h>
+#include "osmo_bits.h"
+
+/*
+ * AMR TRAU parity (same as EFR)
+ *
+ * g(x) = x^3 + x^1 + 1
+ */
+static const struct osmo_crc8gen_code gsm0860_amr_crc3 = {
+	.bits = 3,
+	.poly = 0x3,
+	.init = 0x0,
+	.remainder = 0x7,
+};
+
+static int saved_mode, saved_mode_valid;
+
+static char *fclass_names[4] = {
+	"No_Speech", "Speech_Bad", "Speech_Degraded", "Speech_Good"
+};
+
+static char *nospch_class_names[8] = {
+	"No_Data", "invalid", "invalid", "invalid",
+	"Sid_Bad", "Sid_Update", "Onset", "Sid_First"
+};
 
 static unsigned
 bits_to_num(bits, nbits)
-	uint8_t *bits;
+	ubit_t *bits;
 	unsigned nbits;
 {
 	unsigned accum;
@@ -27,27 +51,154 @@
 	return accum;
 }
 
+static void
+decode_mode_0(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+}
+
+static void
+decode_mode_1(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+}
+
+static void
+decode_mode_2(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+}
+
+static void
+decode_mode_3(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+}
+
+static void
+decode_mode_4(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+}
+
+static void
+decode_mode_5(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+}
+
+static void
+decode_mode_6(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+}
+
+static void
+decode_mode_7(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+}
+
+static void (*per_mode_decode[8])() = {
+	decode_mode_0,
+	decode_mode_1,
+	decode_mode_2,
+	decode_mode_3,
+	decode_mode_4,
+	decode_mode_5,
+	decode_mode_6,
+	decode_mode_7
+};
+
+static void
+decode_speech_frame(c_bits, d_bits, cm_hdr)
+	ubit_t *c_bits, *d_bits;
+	unsigned cm_hdr;
+{
+	unsigned mode;
+
+	if (c_bits[11]) {
+		if (!saved_mode_valid) {
+			printf("  Mode unknown, cannot decode\n");
+			return;
+		}
+		mode = saved_mode;
+		saved_mode_valid = 0;
+	} else {
+		mode = cm_hdr;
+		saved_mode = mode;
+		saved_mode_valid = 1;
+	}
+	printf("  Decoding per speech mode %u\n", mode);
+	per_mode_decode[mode](c_bits, d_bits);
+}
+
+static void
+decode_nospeech_frame(c_bits, d_bits)
+	ubit_t *c_bits, *d_bits;
+{
+	ubit_t crc_collect[25 + 61];
+	int crc_stat;
+
+	printf("  No_Spch_Class=%u%u%u (%s) CMI=%u CMR=%u\n",
+		d_bits[31], d_bits[32], d_bits[33],
+		nospch_class_names[bits_to_num(d_bits + 31, 3)],
+		bits_to_num(d_bits + 34, 3), bits_to_num(d_bits + 37, 3));
+	printf("  PAB=%u TAE=%u%u\n", d_bits[40], d_bits[41], d_bits[42]);
+	bcopy(c_bits, crc_collect, 25);
+	bcopy(d_bits + 31, crc_collect + 25, 61);
+	crc_stat = osmo_crc8gen_check_bits(&gsm0860_amr_crc3, crc_collect,
+					   25 + 61, d_bits + 92);
+	printf("  CRC %s\n", crc_stat ? "bad" : "good");
+	if (crc_stat) {
+		saved_mode_valid = 0;
+	} else {
+		saved_mode = bits_to_num(d_bits + 34, 3);
+		saved_mode_valid = 1;
+	}
+}
+
 void
 print_amr_frame(frame_bits)
 	uint8_t *frame_bits;
 {
-	unsigned c6_11;
+	ubit_t c_bits[25], d_bits[256];
+	uint8_t fclass, cm_hdr;
 
-	c6_11 = bits_to_num(frame_bits + 22, 6);
-	printf("  C6-C11: %u\n", c6_11);
+	bcopy(frame_bits + 17, c_bits, 15);
+	bcopy(frame_bits + 33, c_bits + 15, 10);
+	bcopy(frame_bits + 43, d_bits, 5);
+	bcopy(frame_bits + 49, d_bits + 5, 15);
+	bcopy(frame_bits + 65, d_bits + 20, 15);
+	bcopy(frame_bits + 81, d_bits + 35, 15);
+	bcopy(frame_bits + 97, d_bits + 50, 15);
+	bcopy(frame_bits + 113, d_bits + 65, 15);
+	bcopy(frame_bits + 129, d_bits + 80, 15);
+	bcopy(frame_bits + 145, d_bits + 95, 15);
+	bcopy(frame_bits + 161, d_bits + 110, 15);
+	bcopy(frame_bits + 177, d_bits + 125, 15);
+	bcopy(frame_bits + 193, d_bits + 140, 15);
+	bcopy(frame_bits + 209, d_bits + 155, 15);
+	bcopy(frame_bits + 225, d_bits + 170, 15);
+	bcopy(frame_bits + 241, d_bits + 185, 15);
+	bcopy(frame_bits + 257, d_bits + 200, 15);
+	bcopy(frame_bits + 273, d_bits + 215, 15);
+	bcopy(frame_bits + 289, d_bits + 230, 15);
+	bcopy(frame_bits + 305, d_bits + 245, 11);
+
+	printf("  C6-C11: %u\n", bits_to_num(c_bits + 5, 6));
 	printf("  RIF=%u C13=%u Config_Prot=%u%u%u Msg_No=%u%u\n",
-		frame_bits[28], frame_bits[29], frame_bits[30],
-		frame_bits[31], frame_bits[33], frame_bits[34],
-		frame_bits[35]);
-	printf("  DTXd=%u TFOE=%u FClass=%u%u CMI/CMR=%u%u%u\n",
-		frame_bits[36], frame_bits[37], frame_bits[38],
-		frame_bits[39], frame_bits[40], frame_bits[41],
-		frame_bits[42]);
-	if (!frame_bits[38] && !frame_bits[39])
-		printf("  No_Spch_Class=%u%u%u CMI=%u%u%u CMR=%u%u%u\n",
-			frame_bits[76], frame_bits[77], frame_bits[78],
-			frame_bits[79], frame_bits[81], frame_bits[82],
-			frame_bits[83], frame_bits[84], frame_bits[85]);
+		c_bits[11], c_bits[12], c_bits[13], c_bits[14], c_bits[15],
+		c_bits[16], c_bits[17]);
+	fclass = bits_to_num(c_bits + 20, 2);
+	cm_hdr = bits_to_num(c_bits + 22, 3);
+	printf("  DTXd=%u TFOE=%u FClass=%u%u (%s) %s=%u\n",
+		c_bits[18], c_bits[19], c_bits[20], c_bits[21],
+		fclass_names[fclass], c_bits[11] ? "CMR" : "CMI", cm_hdr);
+	if (fclass)
+		decode_speech_frame(c_bits, d_bits, cm_hdr);
+	else
+		decode_nospeech_frame(c_bits, d_bits);
 	printf("  T1=%u T2=%u T3=%u T4=%u\n", frame_bits[316],
 		frame_bits[317], frame_bits[318], frame_bits[319]);
 }