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hdlc_rec2.c
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hdlc_rec2.c
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// This file is part of Dire Wolf, an amateur radio packet TNC.
//
// Copyright (C) 2011, 2012, 2013, 2014, 2015 John Langner, WB2OSZ
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 2 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//
/********************************************************************************
*
* File: hdlc_rec2.c
*
* Purpose: Extract HDLC frame from a block of bits after someone
* else has done the work of pulling it out from between
* the special "flag" sequences.
*
*
* New in version 1.1:
*
* Several enhancements provided by Fabrice FAURE:
*
* - Additional types of attempts to fix a bad CRC.
* - Optimized code to reduce execution time.
* - Improved detection of duplicate packets from different fixup attempts.
* - Set limit on number of packets in fix up later queue.
*
* One of the new recovery attempt cases recovers three additional
* packets that were lost before. The one thing I disagree with is
* use of the word "swap" because that sounds like two things
* are being exchanged for each other. I would prefer "flip"
* or "invert" to describe changing a bit to the opposite state.
* I took "swap" out of the user-visible messages but left the
* rest of the source code as provided.
*
* Test results: We intentionally use the worst demodulator so there
* is more opportunity to try to fix the frames.
*
* atest -P A -F n 02_Track_2.wav
*
* n description frames sec
* -- ----------- ------ ---
* 0 no attempt 963 40 error-free frames
* 1 invert 1 979 41 16 more
* 2 invert 2 982 42 3 more
* 3 invert 3 982 42 no change
* 4 remove 1 982 43 no change
* 5 remove 2 982 43 no change
* 6 remove 3 982 43 no change
* 7 insert 1 982 45 no change
* 8 insert 2 982 47 no change
* 9 invert two sep 993 178 11 more, some visually obvious errors.
* 10 invert many? 993 190 no change
* 11 remove many 995 190 2 more, need to investigate in detail.
* 12 remove two sep 995 201 no change
*
* Observations: The "insert" and "remove" techniques had no benefit. I would not expect them to.
* We have a phase locked loop that attempts to track any slight variations in the
* timing so we sample near the middle of the bit interval. Bits can get corrupted
* by noise but not disappear or just appear. That would be a gap in the timing.
* These should probably be removed in a future version.
*
*
* Version 1.2: Now works for 9600 baud.
* This was more complicated due to the data scrambling.
* It was necessary to retain more initial state information after
* the start flag octet.
*
*******************************************************************************/
#include <stdio.h>
#include <assert.h>
#include <ctype.h>
//Optimize processing by accessing directly to decoded bits
#define RRBB_C 1
#include "direwolf.h"
#include "hdlc_rec2.h"
#include "fcs_calc.h"
#include "textcolor.h"
#include "ax25_pad.h"
#include "rrbb.h"
#include "rdq.h"
#include "multi_modem.h"
#include "dtime_now.h"
#include "demod_9600.h" /* for descramble() */
#include "audio.h" /* for struct audio_s */
//#include "ax25_pad.h" /* for AX25_MAX_ADDR_LEN */
//#define DEBUG 1
//#define DEBUGx 1
//#define DEBUG_LATER 1
/* Audio configuration. */
static struct audio_s *save_audio_config_p;
/*
* Minimum & maximum sizes of an AX.25 frame including the 2 octet FCS.
*/
#define MIN_FRAME_LEN ((AX25_MIN_PACKET_LEN) + 2)
#define MAX_FRAME_LEN ((AX25_MAX_PACKET_LEN) + 2)
/*
* This is the current state of the HDLC decoder.
*
* It is possible to run multiple decoders concurrently by
* having a separate set of state variables for each.
*
* Should have a reset function instead of initializations here.
*/
struct hdlc_state_s {
int prev_raw; /* Keep track of previous bit so */
/* we can look for transitions. */
/* Should be only 0 or 1. */
int is_scrambled; /* Set for 9600 baud. */
int lfsr; /* Descrambler shift register for 9600 baud. */
int prev_descram; /* Previous unscrambled for 9600 baud. */
unsigned char pat_det; /* 8 bit pattern detector shift register. */
/* See below for more details. */
unsigned char oacc; /* Accumulator for building up an octet. */
int olen; /* Number of bits in oacc. */
/* When this reaches 8, oacc is copied */
/* to the frame buffer and olen is zeroed. */
unsigned char frame_buf[MAX_FRAME_LEN];
/* One frame is kept here. */
int frame_len; /* Number of octets in frame_buf. */
/* Should be in range of 0 .. MAX_FRAME_LEN. */
};
#define MAX_RETRY_SWAP_BITS 24 /* Maximum number of contiguous bits to swap */
#define MAX_RETRY_REMOVE_SEPARATED_BITS 24 /* Maximum number of contiguous bits to remove */
static int try_decode (rrbb_t block, int chan, int subchan, alevel_t alevel, retry_conf_t retry_conf, int passall);
static int try_to_fix_quick_now (rrbb_t block, int chan, int subchan, alevel_t alevel);
static int sanity_check (unsigned char *buf, int blen, retry_t bits_flipped, enum sanity_e sanity_test);
/***********************************************************************************
*
* Name: hdlc_rec2_init
*
* Purpose: Initialization.
*
* Inputs: p_audio_config - Pointer to configuration settings.
* This is what we care about for each channel.
*
* enum retry_e fix_bits;
* Level of effort to recover from
* a bad FCS on the frame.
* 0 = no effort
* 1 = try fixing a single bit
* 2... = more techniques...
*
* enum sanity_e sanity_test;
* Sanity test to apply when finding a good
* CRC after changing one or more bits.
* Must look like APRS, AX.25, or anything.
*
* int passall;
* Allow thru even with bad CRC after exhausting
* all fixup attempts.
*
* Description: Save pointer to configuration for later use.
*
***********************************************************************************/
void hdlc_rec2_init (struct audio_s *p_audio_config)
{
save_audio_config_p = p_audio_config;
}
/***********************************************************************************
*
* Name: hdlc_rec2_block
*
* Purpose: Extract HDLC frame from a stream of bits.
*
* Inputs: block - Handle for bit array.
*
* Description: The other (original) hdlc decoder took one bit at a time
* right out of the demodulator.
*
* This is different in that it processes a block of bits
* previously extracted from between two "flag" patterns.
*
* This allows us to try decoding the same received data more
* than once.
*
* Version 1.2: Now works properly for G3RUH type scrambling.
*
***********************************************************************************/
void hdlc_rec2_block (rrbb_t block)
{
int chan = rrbb_get_chan(block);
int subchan = rrbb_get_subchan(block);
alevel_t alevel = rrbb_get_audio_level(block);
retry_t fix_bits = save_audio_config_p->achan[chan].fix_bits;
int passall = save_audio_config_p->achan[chan].passall;
int ok;
int n;
#if DEBUGx
text_color_set(DW_COLOR_DEBUG);
dw_printf ("\n--- try to decode ---\n");
#endif
/* Create an empty retry configuration */
retry_conf_t retry_cfg;
/*
* For our first attempt we don't try to alter any bits.
* Still let it thru if passall AND no retries are desired.
*/
retry_cfg.type = RETRY_TYPE_NONE;
retry_cfg.mode = RETRY_MODE_CONTIGUOUS;
retry_cfg.retry = RETRY_NONE;
retry_cfg.u_bits.contig.nr_bits = 0;
retry_cfg.u_bits.contig.bit_idx = 0;
/* Prepare the decoded bits in an array for faster processing
*(at cost of memory but 1 or 2 kbytes is nothing compared to processing time ) */
rrbb_compute_bits(block);
ok = try_decode (block, chan, subchan, alevel, retry_cfg, passall & (fix_bits == RETRY_NONE));
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_INFO);
dw_printf ("Got it the first time.\n");
#endif
rrbb_delete (block);
return;
}
/*
* Not successful with frame in orginal form.
* Try the quick techniques with time proportional to the frame length.
*/
if (try_to_fix_quick_now (block, chan, subchan, alevel)) {
rrbb_delete (block);
return;
}
/*
* Not successful with the quick fix up attempts.
* Do we want to try the more aggressive techniques where processing
* time is proportional to the square of length?
* Rather than doing it now, we throw it in a queue for processing
* by a different thread.
*/
if (fix_bits >= RETRY_SWAP_TWO_SEP) {
rdq_append (block);
}
else if (passall) {
/* Exhausted all desired fix up attempts. */
/* Let thru even with bad CRC. Of course, it still */
/* needs to be a minimum number of whole octets. */
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 1);
rrbb_delete (block);
}
else {
rrbb_delete (block);
}
} /* end hdlc_rec2_block */
/***********************************************************************************
*
* Name: try_to_fix_quick_now
*
* Purpose: Attempt some quick fixups that don't take very long.
*
* Inputs: block - Stream of bits that might be a frame.
* chan - Radio channel from which it was received.
* subchan - Which demodulator when more than one per channel.
* alevel - Audio level for later reporting.
*
* Global In: configuration fix_bits - Maximum level of fix up to attempt.
*
* RETRY_NONE (0) - Don't try any.
* RETRY_SWAP_SINGLE (1) - Try inverting single bits.
* etc.
*
* configuration passall - Let it thru with bad CRC after exhausting
* all fixup attempts.
*
*
* Returns: 1 for success. "try_decode" has passed the result along to the
* processing step.
* 0 for failure. Caller might continue with more aggressive attempts.
*
* Description: Some of the attempted fix up techniques are quick.
* We will attempt them immediately after receiving the frame.
* Others, that take time order N**2, will be done in a later section.
*
* Version 1.2: Now works properly for G3RUH type scrambling.
*
***********************************************************************************/
static int try_to_fix_quick_now (rrbb_t block, int chan, int subchan, alevel_t alevel)
{
int ok;
int len, i,j;
retry_t fix_bits = save_audio_config_p->achan[chan].fix_bits;
int passall = save_audio_config_p->achan[chan].passall;
len = rrbb_get_len(block);
/* Prepare the retry configuration */
retry_conf_t retry_cfg;
/* Will modify only contiguous bits*/
retry_cfg.mode = RETRY_MODE_CONTIGUOUS;
/*
* Try fixing one bit.
*/
if (fix_bits < RETRY_SWAP_SINGLE) {
/* Stop before single bit fix up. */
return 0; /* failure. */
}
/* Try to swap one bit */
retry_cfg.type = RETRY_TYPE_SWAP;
retry_cfg.retry = RETRY_SWAP_SINGLE;
retry_cfg.u_bits.contig.nr_bits = 1;
for (i=0; i<len; i++) {
/* Set the index of the bit to swap */
retry_cfg.u_bits.contig.bit_idx = i;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by flipping SINGLE bit %d of %d ***\n", i, len);
#endif
return 1;
}
}
/*
* Try fixing two adjacent bits.
*/
if (fix_bits < RETRY_SWAP_DOUBLE) {
return 0;
}
/* Try to swap two contiguous bits */
retry_cfg.retry = RETRY_SWAP_DOUBLE;
retry_cfg.u_bits.contig.nr_bits = 2;
for (i=0; i<len-1; i++) {
retry_cfg.u_bits.contig.bit_idx = i;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by flipping DOUBLE bit %d of %d ***\n", i, len);
#endif
return 1;
}
}
/*
* Try fixing adjacent three bits.
*/
if (fix_bits < RETRY_SWAP_TRIPLE) {
return 0;
}
/* Try to swap three contiguous bits */
retry_cfg.retry = RETRY_SWAP_TRIPLE;
retry_cfg.u_bits.contig.nr_bits = 3;
for (i=0; i<len-2; i++) {
retry_cfg.u_bits.contig.bit_idx = i;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by flipping TRIPLE bit %d of %d ***\n", i, len);
#endif
return 1;
}
}
if (fix_bits < RETRY_REMOVE_SINGLE) {
return 0;
}
/*
* Try removing one bit.
*/
retry_cfg.type = RETRY_TYPE_REMOVE;
retry_cfg.retry = RETRY_REMOVE_SINGLE;
retry_cfg.u_bits.contig.nr_bits = 1;
for (i=0; i<len; i++) {
retry_cfg.u_bits.contig.bit_idx = i;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by removing SINGLE bit %d of %d ***\n", i, len);
#endif
return 1;
}
}
if (fix_bits < RETRY_REMOVE_DOUBLE) {
return 0;
}
/*
* Try removing two contiguous bits.
*/
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Try removing DOUBLE bits *** for %d bits\n", len);
#endif
retry_cfg.retry = RETRY_REMOVE_DOUBLE;
retry_cfg.u_bits.contig.nr_bits = 2;
for (i=0; i<len-1; i++) {
retry_cfg.u_bits.contig.bit_idx = i;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by removing DOUBLE bits %d of %d ***\n", i, len);
#endif
return 1;
}
}
if (fix_bits < RETRY_REMOVE_TRIPLE) {
return 0;
}
/*
* Try removing three contiguous bits.
*/
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Try removing TRIPLE bits *** for %d bits\n", len);
#endif
retry_cfg.retry = RETRY_REMOVE_TRIPLE;
retry_cfg.u_bits.contig.nr_bits = 3;
for (i=0; i<len-2; i++) {
retry_cfg.u_bits.contig.bit_idx = i;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by removing TRIPLE bits %d of %d ***\n", i, len);
#endif
return 1;
}
}
if (fix_bits < RETRY_INSERT_SINGLE) {
return 0;
}
/*
* Try inserting one bit (two values possibles for this inserted bit).
*/
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Try inserting SINGLE bit *** for %d bits\n", len);
#endif
retry_cfg.type = RETRY_TYPE_INSERT;
retry_cfg.retry = RETRY_INSERT_SINGLE;
retry_cfg.u_bits.contig.nr_bits = 1;
for (i=0; i<len; i++) {
retry_cfg.u_bits.contig.bit_idx = i;
retry_cfg.insert_value=0;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (!ok) {
retry_cfg.insert_value=1;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
}
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by inserting SINGLE bit %d of %d ***\n", i, len);
#endif
return 1;
}
}
if (fix_bits < RETRY_INSERT_DOUBLE) {
return 0;
}
/*
* Try inserting two contiguous bits (4 possible values for two bits).
*/
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Try inserting DOUBLE bits *** for %d bits\n", len);
#endif
retry_cfg.retry = RETRY_INSERT_DOUBLE;
retry_cfg.u_bits.contig.nr_bits = 2;
for (i=0; i<len-1; i++) {
retry_cfg.u_bits.contig.bit_idx = i;
for (j=0;j<4;j++) {
retry_cfg.insert_value=j;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by inserting DOUBLE bits %d of %d ***\n", i, len);
#endif
return 1;
}
}
}
return 0;
}
/***********************************************************************************
*
* Name: hdlc_rec2_try_to_fix_later
*
* Purpose: Attempt some more time-consuming techniques.
* Rather than trying these immediately, the information is
* put into a queue and processed by another thread.
*
* Inputs: block - Stream of bits that might be a frame.
* chan - Radio channel from which it was received.
* subchan - Which demodulator when more than one per channel.
* alevel - Audio level for later reporting.
*
* Global In: configuration fix_bits - Maximum level of fix up to attempt.
*
* RETRY_NONE (0) - Don't try any.
* RETRY_SWAP_SINGLE (1) - Try inverting single bits.
* etc.
*
* configuration passall - Let it thru with bad CRC after exhausting
* all fixup attempts.
*
*
* Returns: 1 for success. "try_decode" has passed the result along to the
* processing step.
* 0 for failure. Caller might try again if "passall" option specified.
*
***********************************************************************************/
int hdlc_rec2_try_to_fix_later (rrbb_t block, int chan, int subchan, alevel_t alevel)
{
int ok;
int len, i, j;
retry_t fix_bits = save_audio_config_p->achan[chan].fix_bits;
int passall = save_audio_config_p->achan[chan].passall;
#if DEBUG_LATER
double tstart, tend;
#endif
retry_conf_t retry_cfg;
len = rrbb_get_len(block);
if (fix_bits < RETRY_SWAP_TWO_SEP) {
goto failure;
}
retry_cfg.mode = RETRY_MODE_SEPARATED;
/*
* Two non-adjacent ("separated") single bits.
* It chews up a lot of CPU time. Test takes 4 times longer to run.
*
* Ran up to xx seconds (TODO check again with optimized code) seconds for 1040 bits before giving up .
* Processing time is order N squared so time goes up rapidly with larger frames.
*/
retry_cfg.type = RETRY_TYPE_SWAP;
retry_cfg.retry = RETRY_SWAP_TWO_SEP;
retry_cfg.u_bits.sep.bit_idx_c = -1;
#ifdef DEBUG_LATER
tstart = dtime_now();
dw_printf ("*** Try flipping TWO SEPARATED BITS %d bits\n", len);
#endif
len = rrbb_get_len(block);
for (i=0; i<len-2; i++) {
retry_cfg.u_bits.sep.bit_idx_a = i;
int j;
ok = 0;
for (j=i+2; j<len; j++) {
retry_cfg.u_bits.sep.bit_idx_b = j;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
break;
}
}
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by flipping TWO SEPARATED bits %d and %d of %d \n", i, j, len);
#endif
return (1);
}
}
#if DEBUG_LATER
tend = dtime_now();
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** No luck flipping TWO SEPARATED bits of %d *** %.3f sec.\n", len, tend-tstart);
#endif
if (fix_bits < RETRY_SWAP_MANY) {
goto failure;
}
/* Try to swap many contiguous bits */
retry_cfg.mode = RETRY_MODE_CONTIGUOUS;
retry_cfg.type = RETRY_TYPE_SWAP;
retry_cfg.retry = RETRY_SWAP_MANY;
#ifdef DEBUG_LATER
tstart = dtime_now();
dw_printf ("*** Try swapping many BITS %d bits\n", len);
#endif
len = rrbb_get_len(block);
for (i=0; i<len; i++) {
for (j=1; j<len-i && j < MAX_RETRY_SWAP_BITS;j++) {
retry_cfg.u_bits.contig.bit_idx = i;
retry_cfg.u_bits.contig.nr_bits = j;
// dw_printf ("*** Trying swapping %d bits starting at %d of %d ***\n", j,i, len);
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by swapping %d bits starting at %d of %d ***\n", j,i, len);
#endif
return (1);
}
}
}
#if DEBUG_LATER
tend = dtime_now();
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** No luck swapping many bits for len %d in %.3f sec.\n",len, tend-tstart);
#endif
if (fix_bits < RETRY_REMOVE_MANY) {
goto failure;
}
/* Try to remove many contiguous bits */
retry_cfg.type = RETRY_TYPE_REMOVE;
retry_cfg.retry = RETRY_REMOVE_MANY;
#ifdef DEBUG_LATER
tstart = dtime_now();
dw_printf ("*** Trying removing many bits for len\n", len);
#endif
len = rrbb_get_len(block);
for (i=0; i<2; i++) {
for (j=1; j<len-i && j<len/2;j++) {
retry_cfg.u_bits.contig.bit_idx = i;
retry_cfg.u_bits.contig.nr_bits = j;
#ifdef DEBUG
dw_printf ("*** Trying removing %d bits starting at %d of %d ***\n", j,i, len);
#endif
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
#if DEBUG
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by removing %d bits starting at %d of %d ***\n", j,i, len);
#endif
return (1);
}
}
}
#if DEBUG_LATER
tend = dtime_now();
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** No luck removing many bits for len %d *** in %.3f sec.\n", len, tend-tstart);
#endif
if (fix_bits < RETRY_REMOVE_TWO_SEP) {
goto failure;
}
/*
* Try to remove Two non-adjacent ("separated") single bits.
*/
retry_cfg.mode = RETRY_MODE_SEPARATED;
retry_cfg.type = RETRY_TYPE_REMOVE;
retry_cfg.retry = RETRY_REMOVE_TWO_SEP;
retry_cfg.u_bits.sep.bit_idx_c = -1;
#if DEBUG_LATER
tstart = dtime_now();
dw_printf ("*** Try removing TWO SEPARATED BITS %d bits\n", len);
#endif
len = rrbb_get_len(block);
for (i=0; i<len-2; i++) {
retry_cfg.u_bits.sep.bit_idx_a = i;
int j;
ok = 0;
for (j=i+2; j<len && j - i < MAX_RETRY_REMOVE_SEPARATED_BITS; j++) {
retry_cfg.u_bits.sep.bit_idx_b = j;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, 0);
if (ok) {
break;
}
}
if (ok) {
#if DEBUG_LATER
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** Success by removing TWO SEPARATED bits %d and %d of %d \n", i, j, len);
#endif
return (1);
}
}
#if DEBUG_LATER
tend = dtime_now();
text_color_set(DW_COLOR_ERROR);
dw_printf ("*** No luck removing TWO SEPARATED bits of %d *** %.3f sec.\n", len, tend-tstart);
#endif
failure:
/*
* All fix up attempts have failed.
* Should we pass it along anyhow with a bad CRC?
* Note that we still need a minimum number of whole octets.
*/
if (passall) {
retry_cfg.type = RETRY_TYPE_NONE;
retry_cfg.mode = RETRY_MODE_CONTIGUOUS;
retry_cfg.retry = RETRY_NONE;
retry_cfg.u_bits.contig.nr_bits = 0;
retry_cfg.u_bits.contig.bit_idx = 0;
ok = try_decode (block, chan, subchan, alevel, retry_cfg, passall);
return (ok);
}
return (0);
} /* end hdlc_rec2_try_to_fix_later */
/*
* Check if the specified index of bit has been modified with the current type of configuration
* Provide a specific implementation for contiguous mode to optimize number of tests done in the loop
*/
inline static char is_contig_bit_modified(int bit_idx, retry_conf_t retry_conf) {
int cont_bit_idx = retry_conf.u_bits.contig.bit_idx;
int cont_nr_bits = retry_conf.u_bits.contig.nr_bits;
if (bit_idx >= cont_bit_idx && (bit_idx < cont_bit_idx + cont_nr_bits ))
return 1;
else
return 0;
}
/*
* Check if the specified index of bit has been modified with the current type of configuration in separated bit index mode
* Provide a specific implementation for separated mode to optimize number of tests done in the loop
*/
inline static char is_sep_bit_modified(int bit_idx, retry_conf_t retry_conf) {
if (bit_idx == retry_conf.u_bits.sep.bit_idx_a ||
bit_idx == retry_conf.u_bits.sep.bit_idx_b ||
bit_idx == retry_conf.u_bits.sep.bit_idx_c)
return 1;
else
return 0;
}
/*
* Get the bit value from a precalculated array to optimize access time in the loop
*/
inline static unsigned int get_bit (const rrbb_t b,const unsigned int ind)
{
return b->computed_data[ind];
}
/***********************************************************************************
*
* Name: try_decode
*
* Purpose:
*
* Inputs: block - Bit string that was collected between "flag" patterns.
*
* chan, subchan - where it came from.
*
* alevel - audio level for later reporting.
*
* retry_conf - Controls changes that will be attempted to get a good CRC.
*
* retry:
* Level of effort to recover from A bad FCS on the frame.
* RETRY_NONE=0,
* RETRY_SWAP_SINGLE=1,
* RETRY_SWAP_DOUBLE=2,
* RETRY_SWAP_TRIPLE=3,
* RETRY_REMOVE_SINGLE=4,
* RETRY_REMOVE_DOUBLE=5,
* RETRY_REMOVE_TRIPLE=6,
* RETRY_INSERT_SINGLE=7,
* RETRY_INSERT_DOUBLE=8,
* RETRY_SWAP_TWO_SEP=9,
* RETRY_SWAP_MANY=10,
* RETRY_REMOVE_MANY=11,
* RETRY_REMOVE_TWO_SEP=12,
*
* mode: RETRY_MODE_CONTIGUOUS - change adjacent bits.
* contig.bit_idx - first bit position
* contig.nr_bits - number of bits
*
* RETRY_MODE_SEPARATED - change bits not next to each other.
* sep.bit_idx_a - bit positions
* sep.bit_idx_b - bit positions
* sep.bit_idx_c - bit positions
*
* type: RETRY_TYPE_NONE - Make no changes.
* RETRY_TYPE_SWAP - Try inverting.
* RETRY_TYPE_REMOVE - Try removing.
* RETRY_TYPE_INSERT - Try inserting.
*
* passall - All it thru even with bad CRC.
* Valid only when no changes make. i.e.
* retry == RETRY_NONE, type == RETRY_TYPE_NONE
*
* Returns: 1 = successfully extracted something.
* 0 = failure.
*
***********************************************************************************/
static int try_decode (rrbb_t block, int chan, int subchan, alevel_t alevel, retry_conf_t retry_conf, int passall)
{
struct hdlc_state_s H;
int blen; /* Block length in bits. */
int i;
unsigned int raw; /* From demodulator. */
int crc_failed = 1;
int retry_conf_mode = retry_conf.mode;
int retry_conf_type = retry_conf.type;
int retry_conf_retry = retry_conf.retry;
H.is_scrambled = rrbb_get_is_scrambled (block);
H.prev_descram = rrbb_get_prev_descram (block);
H.lfsr = rrbb_get_descram_state (block);
H.prev_raw = get_bit (block, 0); /* Actually last bit of the */
/* opening flag so we can derive the */
/* first data bit. */
/* Does this make sense? */
/* This is the last bit of the "flag" pattern. */
/* If it was corrupted we wouldn't have detected */
/* the start of frame. */
if ((retry_conf.mode == RETRY_MODE_CONTIGUOUS && is_contig_bit_modified(0, retry_conf)) ||
(retry_conf.mode == RETRY_MODE_SEPARATED && is_sep_bit_modified(0, retry_conf))) {
H.prev_raw = ! H.prev_raw;
}
H.pat_det = 0;
H.oacc = 0;
H.olen = 0;
H.frame_len = 0;
blen = rrbb_get_len(block);
/* Prepare space for the inserted bits in contiguous mode (separated mode for insert is not supported yet) */
if (retry_conf.type == RETRY_TYPE_INSERT && retry_conf.mode == RETRY_MODE_CONTIGUOUS)
blen+=retry_conf.u_bits.contig.nr_bits;
#if DEBUGx
text_color_set(DW_COLOR_DEBUG);
if (retry_conf.type == RETRY_TYPE_NONE)
dw_printf ("try_decode: blen=%d\n", blen);
#endif
for (i=1; i<blen; i++) {
/* Get the value for the current bit */
raw = get_bit (block, i);
/* If swap two sep mode , swap the bit if needed */
if (retry_conf_retry == RETRY_SWAP_TWO_SEP) {
if (is_sep_bit_modified(i, retry_conf))
raw = ! raw;
/* Else if remove two sep bits mode , remove the bit if needed */
} else if (retry_conf_retry == RETRY_REMOVE_TWO_SEP) {
if (is_sep_bit_modified(i, retry_conf))
//Remove (ignore) this bit from the buffer!
continue;
}
/* Else handle all the others contiguous modes */
else if (retry_conf_mode == RETRY_MODE_CONTIGUOUS) {
/* If contiguous remove, ignore this bit from the buffer */
if (retry_conf_type == RETRY_TYPE_REMOVE) {
if ( is_contig_bit_modified(i, retry_conf))
//Remove (ignore) this bit from the buffer!
continue;
}
/* If insert bits mode */
else if (retry_conf_type == RETRY_TYPE_INSERT) {
int nr_bits = retry_conf.u_bits.contig.nr_bits;
int bit_idx = retry_conf.u_bits.contig.bit_idx;
/* If bit is after the index to insert, use the existing bit value (but shifted from the array) */
if (i >= bit_idx + nr_bits)
raw = get_bit (block, i-nr_bits);
/* Else if this is a bit to insert, calculate the value of the bit from insert_value */
else if (is_contig_bit_modified(i, retry_conf)) {
raw = (retry_conf.insert_value >> (i-bit_idx)) & 1;
/* dw_printf ("raw is %d for i %d bit_idx %d insert_value %d\n",
raw, i, bit_idx, retry_conf.insert_value);*/
/* Else use the original bit value from the buffer */
} else {
/* Already set before */
}
/* If in swap mode */
} else if (retry_conf_type == RETRY_TYPE_SWAP) {
/* If this is the bit to swap */
if (is_contig_bit_modified(i, retry_conf))
raw = ! raw;
}
} else {
}
/*
* Octets are sent LSB first.
* Shift the most recent 8 bits thru the pattern detector.
*/
H.pat_det >>= 1;
/*
* Using NRZI encoding,
* A '0' bit is represented by an inversion since previous bit.
* A '1' bit is represented by no change.
* Note: this code can be factorized with the raw != H.prev_raw code at the cost of processing time
*/
int dbit ;
if (H.is_scrambled) {
int descram;
descram = descramble(raw, &(H.lfsr));
dbit = (descram == H.prev_descram);
H.prev_descram = descram;
H.prev_raw = raw;
}
else {
dbit = (raw == H.prev_raw);
H.prev_raw = raw;
}
if (dbit) {
H.pat_det |= 0x80;