--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/frtest/cvt-dlcap.c	Sun Nov 20 06:11:16 2022 +0000
@@ -0,0 +1,87 @@
+/*
+ * This program reads a TCH downlink capture produced with FreeCalypso tools
+ * (fw version with TCH downlink sniffing feature and fc-shell tch record)
+ * and converts it into our extended-libgsm binary format, to be further
+ * fed to gsmfr-decode.
+ */
+
+#include <sys/types.h>
+#include <ctype.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+static const char bfi_marker[2] = {0xBF, 0x00};
+
+static
+decode_hex_digit(ch)
+{
+	if (isdigit(ch))
+		return(ch - '0');
+	else if (isupper(ch))
+		return(ch - 'A' + 10);
+	else
+		return(ch - 'a' + 10);
+}
+
+main(argc, argv)
+	char **argv;
+{
+	FILE *inf, *outf;
+	char linebuf[128];
+	int lineno;
+	char *cp;
+	int i;
+	u_short status_words[3];
+	u_char tidsp_bytes[33], libgsm_bytes[33];
+
+	if (argc != 3) {
+		fprintf(stderr, "usage: %s infile outfile\n", argv[0]);
+		exit(1);
+	}
+	inf = fopen(argv[1], "r");
+	if (!inf) {
+		perror(argv[1]);
+		exit(1);
+	}
+	outf = fopen(argv[2], "w");
+	if (!outf) {
+		perror(argv[2]);
+		exit(1);
+	}
+	for (lineno = 1; fgets(linebuf, sizeof linebuf, inf); lineno++) {
+		/* grok DSP status words */
+		cp = linebuf;
+		for (i = 0; i < 3; i++) {
+			if (!isxdigit(cp[0]) || !isxdigit(cp[1]) ||
+			    !isxdigit(cp[2]) || !isxdigit(cp[3])) {
+invalid:			fprintf(stderr,
+				    "error: %s is not in the expected format\n",
+						argv[1]);
+				exit(1);
+			}
+			status_words[i] = (decode_hex_digit(cp[0]) << 12) |
+					  (decode_hex_digit(cp[1]) << 8) |
+					  (decode_hex_digit(cp[2]) << 4) |
+					   decode_hex_digit(cp[3]);
+			cp += 4;
+			if (*cp++ != ' ')
+				goto invalid;
+		}
+		/* read the frame bits */
+		for (i = 0; i < 33; i++) {
+			if (!isxdigit(cp[0]) || !isxdigit(cp[1]))
+				goto invalid;
+			tidsp_bytes[i] = (decode_hex_digit(cp[0]) << 4) |
+					  decode_hex_digit(cp[1]);
+			cp += 2;
+		}
+		/* bit 2 of status word 0 is BFI */
+		if (status_words[0] & 0x0004)
+			fwrite(bfi_marker, 1, 2, outf);
+		else {
+			gsm0610_tidsp_to_libgsm(tidsp_bytes, libgsm_bytes);
+			fwrite(libgsm_bytes, 1, 33, outf);
+		}
+	}
+	exit(0);
+}