First fully-working BCH code.

Author: dtiller

src/CMakeLists.txt

@@ -86,6 +86,7 @@ list(APPEND direwolf_SOURCES
   dwgpsd.c
   mheard.c
   eotd.c
+  bch.c
   )
 
 if(LINUX)
@@ -319,6 +320,7 @@ list(APPEND atest_SOURCES
   tt_text.c
   textcolor.c
   eotd.c
+  bch.c
   )
 
 if(WIN32 OR CYGWIN)

src/bch.c

@@ -518,7 +518,7 @@ int apply_bch(const bch_t *bch, int *recd)
 }
 
 /* LEFT justified in hex */
-void bytes_to_bits(const int *bytes, int *bit_dest, int num_bits) {
+void bytes_to_bits(const uint8_t *bytes, int *bit_dest, int num_bits) {
 	for (int i = 0; i < num_bits; i++) {
 		int index = i / 8;
 		int bit_pos = 7 - (i % 8);
@@ -527,7 +527,7 @@ void bytes_to_bits(const int *bytes, int *bit_dest, int num_bits) {
 	}
 }
 
-void bits_to_bytes(const int *bits, int *byte_dest, int num_bits) {
+void bits_to_bytes(const int *bits, uint8_t *byte_dest, int num_bits) {
 
 	int index;
 
@@ -540,8 +540,6 @@ void bits_to_bytes(const int *bits, int *byte_dest, int num_bits) {
 		byte_dest[index] <<= 1;
 		byte_dest[index] |= (bits[i] & 0x01);
 	}
-
-	byte_dest[index] <<= 8 - (num_bits % 8);
 }
 
 void swap_format(const int *bits, int *dest, int cutoff, int num_bits) {
@@ -555,8 +553,8 @@ void swap_format(const int *bits, int *dest, int cutoff, int num_bits) {
 	}
 }
 
-int rotate_byte(int x) {
-        int y = 0;
+uint8_t rotate_byte(uint8_t x) {
+        uint8_t y = 0;
 
         for (int i = 0; i < 8; i++) {
                 y <<= 1;
@@ -583,143 +581,16 @@ void dump_bch(const bch_t *bch) {
 	printf("m: %d length: %d t: %d n: %d k: %d\n", bch->m, bch->length, bch->t, bch->n, bch->k);
 }
 
-void print_array(const char *msg, const char *format, const int *bytes, int num_bytes) {
+void print_bytes(const char *msg, const uint8_t *bytes, int num_bytes) {
 	printf("%s", msg);
 	for (int i = 0; i < num_bytes; i++) {
-		printf(format, bytes[i]);
+		printf("%02x ", bytes[i]);
 	}
 }
 
-void print_bytes(const char *msg, const int *bytes, int num_bytes) {
-	print_array(msg, "%02x ", bytes, num_bytes);
-}
-
 void print_bits(const char *msg, const int *bits, int num_bits) {
-	print_array(msg, "%d ", bits, num_bits);
-}
-
-#undef MAIN
-#undef TEST_BYTES_TO_BITS
-#define TEST_SWAP
-#ifdef MAIN
-int main()
-{
-	int test[][8] = {
-/* 0 errors */	{ 0xb2, 0x17, 0xa2, 0xb9, 0x53, 0xdd, 0xc5, 0x52 }, /* perfect random test */
-                { 0xf0, 0x5a, 0x6a, 0x6a, 0x01, 0x63, 0x33, 0xd0 }, /* g001-cut-lenthened_457.938M.wav */
-                { 0xf0, 0x81, 0x52, 0x6b, 0x71, 0xa5, 0x63, 0x08 }, /* 1st in eotd_received_data */
-/* 3 errors */	{ 0xf0, 0x85, 0x50, 0x6a, 0x01, 0xe5, 0x6e, 0x84 }, /* 2nd in eotd_received_data - 3 bad bits */
-/* 0 errors */	{ 0xf0, 0x85, 0x50, 0x6a, 0x01, 0xe5, 0x06, 0x84 }, /* 2nd, but with the bits fixed */
-/* 3 errors */	{ 0xf0, 0x85, 0x59, 0x5a, 0x01, 0xe5, 0x6e, 0x84 }, /* 3rd - 3 bad bits */
-/* 0 errors */	{ 0xb0, 0x85, 0x59, 0x5a, 0x11, 0xe5, 0x6f, 0x84 }, /* 3rd fixed */
-                { 0xf1, 0x34, 0x50, 0x1a, 0x01, 0xe5, 0x66, 0xfe }, /* 4th */
-                { 0xf0, 0xeb, 0x10, 0xea, 0x01, 0x6e, 0x54, 0x1c }, /* 5th */
-                { 0xf0, 0xea, 0x5c, 0xea, 0x01, 0x6e, 0x55, 0x0e }, /* 6th */
-                { 0xe0, 0x21, 0x10, 0x1a, 0x01, 0x32, 0xbc, 0xe4 }, /* Sun Mar 20 05:41:00 2022 */
-                { 0xf0, 0x42, 0x50, 0x5b, 0xcf, 0xd5, 0x64, 0xe4 }, /* Sun Mar 20 12:58:43 2022 */
-                { 0xf0, 0x8c, 0x10, 0xaa, 0x01, 0x73, 0x7b, 0x1a }, /* Sun Mar 20 13:35:48 2022 */
-                { 0xf0, 0x8c, 0x10, 0xb1, 0xc0, 0xe0, 0x90, 0x64 }, /* Sun Mar 20 13:37:05 2022 */
-/* 3 errors */	{ 0xf0, 0x8c, 0x10, 0x6a, 0x01, 0x64, 0x7a, 0xe8 }, /* Sun Mar 20 13:37:48 2022  - 3 bad bits */
-/* 0 errors */	{ 0x50, 0x8c, 0x12, 0x6a, 0x01, 0x64, 0x7a, 0xe8 }, /* Sun Mar 20 13:37:48 2022 with bits fixed */
-	};
-
-	int bits[63];
-	int temp[8];
-	bch_t bch;
-
-	init_bch(&bch, 6, 63, 3);
-
-	for (int count = 0; count < sizeof(test) / sizeof(*test); count++) {
-		bytes_to_bits(test[count], bits, 63);
-
-		printf("--------------------------\nORIG pkt [%d] ", count);
-		for (int i = 0; i < 8; i++) {
-			printf("%02x ", test[count][i]);
-		}
-		printf("\n");
-
-#ifdef TEST_BYTES_TO_BITS
-	
-		printf("ORIG pkt[%d] bits\n", count);
-		for (int i = 0; i < 63; i++) {
-			printf("%d ", bits[i]);
-		}
-		printf("\n");
-
-		bits_to_bytes(bits, temp, 63);
-		printf("bits_to_bytes pkt [%d]\n", count);
-		for (int i = 0; i < 8; i++) {
-			printf("%02x ", temp[i]);
-		}
-		printf("\n");
-
-#endif
-
-#ifdef TEST_GENERATE	
-		int bch_code[18];
-		generate_bch(&bch, bits, bch_code);
-		printf("generated BCH\n");
-		for (int i = 0; i < 18; i++) {
-			printf("%d ", bch_code[i]);
-		}
-		printf("\n");
-#endif	
-
-#ifdef TEST_SWAP
-		printf("orig: ");
-		for (int i = 0; i < 63; i++) {
-			printf("%d ", bits[i]);
-		}
-		printf("\n");
-
-		swap_format(bits, 45, 63);
-
-		printf("rev:  ");
-		for (int i = 0; i < 63; i++) {
-			printf("%d ", bits[i]);
-		}
-		printf("\n");
-#endif
-#ifdef TEST_APPLY
-		int recv[63];
-
-		for (int i = 0; i < 63; i++) {
-			recv[i] = bits[i];
-		}
-/*	
-		printf("rearranged packet [%d]: ", count);
-		for (int i = 0; i < 63; i++) {
-			printf("%d ", recv[i]);
-		}
-		printf("\n");
-
-		bits_to_bytes(recv, temp, 63);
-
-		printf("original [%d] bytes: ", count);
-		for (int i = 0; i < 8; i++) {
-			printf("%02x ", temp[i]);
-		}
-		printf("\n");
-*/	
-		int corrected = apply_bch(&bch, recv);
-
-		if (corrected >= 0) {
-/*
-			printf("corrected [%d] packet: ", corrected);
-			for (int i = 0; i < 63; i++) {
-				printf("%d ", recv[i]);
-			}
-			printf("\n");
-*/
-			bits_to_bytes(recv, temp, 63);
-
-			printf("corrected [%d] bytes: ", corrected);
-			for (int i = 0; i < 8; i++) {
-				printf("%02x ", temp[i]);
-			}
-			printf("\n");
-		}
-#endif
+	printf("%s", msg);
+	for (int i = 0; i < num_bits; i++) {
+		printf("%d ", bits[i]);
 	}
 }
-#endif

src/bch.h

@@ -1,5 +1,6 @@
 #ifndef __BCH_H
 #define __BCH_H
+#include <stdlib.h>
 
 struct bch {
 	int m;		// 2^m - 1 is max length, n
@@ -21,17 +22,17 @@ void generate_bch(bch_t *bch, const int *data, int *bb);
 
 int apply_bch(const bch_t *bch, int *recd);
 
-void bytes_to_bits(const int *bytes, int *bit_dest, int num_bits);
+void bytes_to_bits(const uint8_t *bytes, int *bit_dest, int num_bits);
 
-void bits_to_bytes(const int *bits, int *byte_dest, int num_bits);
+void bits_to_bytes(const int *bits, uint8_t *byte_dest, int num_bits);
 
 void swap_format(const int *bits, int *dest, int cutoff, int num_bits);
 
-int rotate_byte(int x);
+uint8_t rotate_byte(uint8_t x);
 
 void rotate_bits(const int *in, int *out, int num_bits);
 
-void print_bytes(const char *msg, const int *bytes, int num_bytes);
+void print_bytes(const char *msg, const uint8_t *bytes, int num_bytes);
 
 void print_bits(const char *msg, const int *bits, int num_bits);
 

src/eotd.c

@@ -40,7 +40,7 @@
 #include "eotd_defs.h"
 #include "eotd.h"
 
-#define EOTD_RAW
+#undef EOTD_RAW
 #define EOTD_TIMESTAMP
 #define EOTD_APPEND_HEX
 
@@ -283,7 +283,11 @@ void eotd_to_text (unsigned char *eotd, int eotd_len, char *text, int text_size)
 	add_comma(text, text_size);
 	snprintf(hex, sizeof(hex), "%llx", pkt);
 	strlcat(text, "hex=", text_size);
-	strlcat(text, hex, text_size);
+	for (int i = 56; i >= 0; i -= 8) {
+		sprintf(hex, "%02x ", (unsigned char) (pkt >> i) & 0xff);
+		strlcat(text, hex, text_size);
+	}
+	text[strlen(text) - 1] = '\0'; // zap trailing space
 #endif
 #else
 	char temp[8];

src/hdlc_rec.c

@@ -33,6 +33,7 @@
 #include <assert.h>
 #include <string.h>
 #include <stdint.h>          // uint64_t
+#include <stdlib.h>
 
 //#include "tune.h"
 #include "demod.h"
@@ -46,6 +47,7 @@
 #include "demod_9600.h"		/* for descramble() */
 #include "ptt.h"
 #include "fx25.h"
+#include "bch.h"
 #include "eotd_defs.h"
 
 
@@ -233,7 +235,6 @@ static int my_rand (void) {
 static void eas_rec_bit (int chan, int subchan, int slice, int raw, int future_use)
 {
 	struct hdlc_state_s *H;
-
 /*
  * Different state information for each channel / subchannel / slice.
  */
@@ -408,6 +409,85 @@ a good modem here and providing a result when it is received.
 
 */
 
+
+int is_eotd_valid(struct hdlc_state_s *H) {
+/*
+	The data as received in the frame buffer is in HCB+ATAD format; that is, the first
+	(leftmost) bit is the dummy bit or odd parity bit (which is the last bit transmitted)
+	followed by the BCH code (LSB first, so HCB) followed by the DATA, LSB first (ATAD).
+
+	The apply_bch funtion requires the packet in int[63] format, with the bits arranged
+	in either BCH+ATAD or ATAD+BCH format. Very odd. We'll use the first one.
+*/
+	static uint8_t r2f_mask[] = {0x07, 0x76, 0xa0 };
+	static bch_t *bch_r2f = NULL;
+	static bch_t *bch_f2r = NULL;
+
+	int bits[64];
+
+	assert(H != NULL);
+	// +1 for 'type' byte at end
+	assert(H->frame_len == EOTD_LENGTH + 1);
+
+	if(bch_r2f == NULL) {
+		bch_r2f = malloc(sizeof(bch_t));
+		int status = init_bch(bch_r2f, 6, 63, 3);
+		if (status != 0) {
+			fprintf(stderr, "BCH_R2F initialization failed: %d", status);
+			free(bch_r2f);
+			bch_r2f = NULL;
+			return status;
+		}
+	}
+
+	if(bch_f2r == NULL) {
+		bch_f2r = malloc(sizeof(bch_t));
+		int status = init_bch(bch_f2r, 6, 63, 6);
+		if (status != 0) {
+			fprintf(stderr, "BCH_F2R initialization failed: %d", status);
+			free(bch_f2r);
+			bch_f2r = NULL;
+			return status;
+		}
+	}
+
+	int temp_bits[64];
+	bch_t *temp_bch;
+
+	if (H->eotd_type == EOTD_TYPE_F2R) {
+		temp_bch = bch_f2r;
+	} else {
+		temp_bch = bch_r2f;
+		// The HCB needs to be XOR'ed with a special constant.
+print_bytes("IN  BYTES: ", H->frame_buf, H->frame_len);printf("\n");
+		for (int i = 0; i < sizeof(r2f_mask); i++) {
+			H->frame_buf[i] ^= r2f_mask[i];
+		}
+print_bytes("XOR BYTES: ", H->frame_buf, H->frame_len);printf("\n");
+	}
+
+	int crc_len = temp_bch->n - temp_bch->k;
+
+	bytes_to_bits(H->frame_buf, bits, 64);
+
+	// +1 is to skip the dummy/parity bit.
+	rotate_bits(bits + 1 , temp_bits, crc_len);
+	memcpy(bits + 1, temp_bits, crc_len * sizeof(int));
+print_bits("BCH+ATAD : ", bits, 64);printf("\n");
+
+	// Note: bits are changed in-place.
+	int corrected = apply_bch(temp_bch, bits + 1);
+printf("Corrected %d\n", corrected);
+	// Put back in HCB+ATAD format
+	rotate_bits(bits + 1, temp_bits, crc_len);
+	memcpy(bits + 1, temp_bits, crc_len * sizeof(int));
+print_bits("COR BITS: ", bits, 64);printf("\n");
+	bits_to_bytes(bits, H->frame_buf, 64);
+print_bytes("COR BYTES: ", H->frame_buf, H->frame_len);printf("\n");
+
+	return corrected;
+}
+
 /***********************************************************************************
  *
  * Name:	eotd_rec_bit
@@ -480,17 +560,19 @@ dw_printf("chan=%d subchan=%d slice=%d raw=%d\n", chan, subchan, slice, raw);
 	      H->frame_buf[EOTD_LENGTH] = H->eotd_type;
 	      done = 1;
 #ifdef EOTD_DEBUG
-for (int ii=0; ii < EOTD_MAX_LENGTH; ii++) {dw_printf("%02x ", H->frame_buf[ii]); } dw_printf("\n");
+for (int ii=0; ii < EOTD_LENGTH; ii++) {dw_printf("%02x ", H->frame_buf[ii]); } dw_printf("\n");
 #endif
 	    }
 	}
 
 	if (done) {
 #ifdef DEBUG_E
-	  dw_printf ("frame_buf %d = %s\n", slice, H->frame_buf);
+	  dw_printf ("frame_buf %d = %*s\n", slice, H->frame_len, H->frame_buf);
 #endif
-	  alevel_t alevel = demod_get_audio_level (chan, subchan);
-	  multi_modem_process_rec_frame (chan, subchan, slice, H->frame_buf, H->frame_len, alevel, 0, 0);
+	  if (is_eotd_valid(H) >= 0) {
+	  	alevel_t alevel = demod_get_audio_level (chan, subchan);
+	  	multi_modem_process_rec_frame (chan, subchan, slice, H->frame_buf, H->frame_len, alevel, 0, 0);
+	  }
 
 	  H->eotd_acc = 0;
 	  H->eotd_gathering = 0;