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direwolf/hdlc_rec.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_rec.c
*
* Purpose: Extract HDLC frames from a stream of bits.
*
*******************************************************************************/
#include "direwolf.h"
#include <stdio.h>
#include <assert.h>
#include <string.h>
#include "demod.h"
#include "hdlc_rec.h"
#include "hdlc_rec2.h"
#include "fcs_calc.h"
#include "textcolor.h"
#include "ax25_pad.h"
#include "rrbb.h"
#include "multi_modem.h"
#include "demod_9600.h" /* for descramble() */
#include "ptt.h"
//#define TEST 1 /* Define for unit testing. */
//#define DEBUG3 1 /* monitor the data detect signal. */
/*
* 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 lfsr; /* Descrambler shift register for 9600 baud. */
int prev_descram; /* Previous descrambled for 9600 baud. */
unsigned char pat_det; /* 8 bit pattern detector shift register. */
/* See below for more details. */
unsigned int flag4_det; /* Last 32 raw bits to look for 4 */
/* flag patterns in a row. */
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. */
/* The value of -1 is a special case meaning */
/* bits should not be accumulated. */
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. */
int data_detect; /* True when HDLC data is detected. */
/* This will not be triggered by voice or other */
/* noise or even tones. */
rrbb_t rrbb; /* Handle for bit array for raw received bits. */
};
static struct hdlc_state_s hdlc_state[MAX_CHANS][MAX_SUBCHANS][MAX_SLICERS];
static int num_subchan[MAX_CHANS]; //TODO1.2 use ptr rather than copy.
static int composite_dcd[MAX_CHANS][MAX_SUBCHANS+1];
/***********************************************************************************
*
* Name: hdlc_rec_init
*
* Purpose: Call once at the beginning to initialize.
*
* Inputs: None.
*
***********************************************************************************/
static int was_init = 0;
void hdlc_rec_init (struct audio_s *pa)
{
int ch, sub, slice;
struct hdlc_state_s *H;
//text_color_set(DW_COLOR_DEBUG);
//dw_printf ("hdlc_rec_init (%p) \n", pa);
assert (pa != NULL);
memset (composite_dcd, 0, sizeof(composite_dcd));
for (ch = 0; ch < MAX_CHANS; ch++)
{
if (pa->achan[ch].valid) {
num_subchan[ch] = pa->achan[ch].num_subchan;
assert (num_subchan[ch] >= 1 && num_subchan[ch] <= MAX_SUBCHANS);
for (sub = 0; sub < num_subchan[ch]; sub++)
{
for (slice = 0; slice < MAX_SLICERS; slice++) {
H = &hdlc_state[ch][sub][slice];
H->olen = -1;
// TODO: FIX13 wasteful if not needed.
// Should loop on number of slicers, not max.
H->rrbb = rrbb_new(ch, sub, slice, pa->achan[ch].modem_type == MODEM_SCRAMBLE, H->lfsr, H->prev_descram);
}
}
}
}
hdlc_rec2_init (pa);
was_init = 1;
}
/***********************************************************************************
*
* Name: hdlc_rec_bit
*
* Purpose: Extract HDLC frames from a stream of bits.
*
* Inputs: chan - Channel number.
*
* subchan - This allows multiple demodulators per channel.
*
* slice - Allows multiple slicers per demodulator (subchannel).
*
* raw - One bit from the demodulator.
* should be 0 or 1.
*
* is_scrambled - Is the data scrambled?
*
* descram_state - Current descrambler state. (not used - remove)
*
*
* Description: This is called once for each received bit.
* For each valid frame, process_rec_frame()
* is called for further processing.
*
***********************************************************************************/
// TODO: int not_used_remove
void hdlc_rec_bit (int chan, int subchan, int slice, int raw, int is_scrambled, int not_used_remove)
{
int dbit; /* Data bit after undoing NRZI. */
/* Should be only 0 or 1. */
struct hdlc_state_s *H;
assert (was_init == 1);
assert (chan >= 0 && chan < MAX_CHANS);
assert (subchan >= 0 && subchan < MAX_SUBCHANS);
assert (slice >= 0 && slice < MAX_SLICERS);
/*
* Different state information for each channel / subchannel / slice.
*/
H = &hdlc_state[chan][subchan][slice];
/*
* Using NRZI encoding,
* A '0' bit is represented by an inversion since previous bit.
* A '1' bit is represented by no change.
*/
if (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;
}
/*
* Octets are sent LSB first.
* Shift the most recent 8 bits thru the pattern detector.
*/
H->pat_det >>= 1;
if (dbit) {
H->pat_det |= 0x80;
}
H->flag4_det >>= 1;
if (dbit) {
H->flag4_det |= 0x80000000;
}
/*
* "Data Carrier detect" function based on data patterns rather than
* audio signal strength.
*
* Idle time, at beginning of transmission should be filled
* with the special "flag" characters.
*
* Idle time of all zero bits (alternating tones at maximum rate)
* has also been observed rarely. It is easy to understand the reasoning.
* The tones alternate at the maximum rate, making it symmetrical and providing
* the most opportunity for the PLL to lock on to the edges.
* It also violates the published protocol spec.
*
* Recognize zero(s) followed by a single flag even though it violates the spec.
*
* It has been reported that the TinyTrak4 does this.
* https://groups.yahoo.com/neo/groups/direwolf_packet/conversations/messages/1207
*/
/*
* Originally, this looked for 4 flags in a row or 3 zeros and a flag.
* Is that too fussy?
* Here are the numbers of start of DCD for our favorite Track 2 test.
*
* 7e7e7e7e 504 7e000000 32
* 7e7e7e-- 513 7e0000-- 33
* 7e7e---- 555 7e00---- 42
* 7e------ 2088
*
* I don't think we want to look for a single flag because that would
* make DCD too sensitive to noise and it would interfere with waiting for a
* clear channel to transmit. Even a two byte match causes a lot of flickering
* when listening to live signals. Let's try 3 and see how that works out.
*/
//if (H->flag4_det == 0x7e7e7e7e) {
if ((H->flag4_det & 0xffffff00) == 0x7e7e7e00) {
//if ((H->flag4_det & 0xffff0000) == 0x7e7e0000) {
if ( ! H->data_detect) {
H->data_detect = 1;
dcd_change (chan, subchan, slice, 1);
}
}
//else if (H->flag4_det == 0x7e000000) {
else if ((H->flag4_det & 0xffffff00) == 0x7e000000) {
//else if ((H->flag4_det & 0xffff0000) == 0x7e000000) {
if ( ! H->data_detect) {
H->data_detect = 1;
dcd_change (chan, subchan, slice, 1);
}
}
/*
* Loss of signal should result in lack of transitions.
* (all '1' bits) for at least a little while.
*
* When this was written, I was only concerned about 1200 baud.
* For 9600, added later, there is a (de)scrambling function.
* So if there is no change in the signal, we would get pseudo random bits here.
* Maybe we need to put in another check earlier so DCD is not held on too long
* after loss of signal for 9600.
* No, that would not be a good idea. part of a valid frame, when scrambled,
* could have seven or more "1" bits in a row.
* Needs more study.
*/
if (H->pat_det == 0xff) {
if ( H->data_detect ) {
H->data_detect = 0;
dcd_change (chan, subchan, slice, 0);
}
}
/*
* End of data carrier detect.
*
* The rest is concerned with framing.
*/
rrbb_append_bit (H->rrbb, raw);
if (H->pat_det == 0x7e) {
rrbb_chop8 (H->rrbb);
/*
* The special pattern 01111110 indicates beginning and ending of a frame.
* If we have an adequate number of whole octets, it is a candidate for
* further processing.
*
* It might look odd that olen is being tested for 7 instead of 0.
* This is because oacc would already have 7 bits from the special
* "flag" pattern before it is detected here.
*/
#if OLD_WAY
#if TEST
text_color_set(DW_COLOR_DEBUG);
dw_printf ("\nfound flag, olen = %d, frame_len = %d\n", olen, frame_len);
#endif
if (H->olen == 7 && H->frame_len >= MIN_FRAME_LEN) {
unsigned short actual_fcs, expected_fcs;
#if TEST
int j;
dw_printf ("TRADITIONAL: frame len = %d\n", H->frame_len);
for (j=0; j<H->frame_len; j++) {
dw_printf (" %02x", H->frame_buf[j]);
}
dw_printf ("\n");
#endif
/* Check FCS, low byte first, and process... */
/* Alternatively, it is possible to include the two FCS bytes */
/* in the CRC calculation and look for a magic constant. */
/* That would be easier in the case where the CRC is being */
/* accumulated along the way as the octets are received. */
/* I think making a second pass over it and comparing is */
/* easier to understand. */
actual_fcs = H->frame_buf[H->frame_len-2] | (H->frame_buf[H->frame_len-1] << 8);
expected_fcs = fcs_calc (H->frame_buf, H->frame_len - 2);
if (actual_fcs == expected_fcs) {
alevel_t alevel = demod_get_audio_level (chan, subchan);
multi_modem_process_rec_frame (chan, subchan, slice, H->frame_buf, H->frame_len - 2, alevel, RETRY_NONE); /* len-2 to remove FCS. */
}
else {
#if TEST
dw_printf ("*** actual fcs = %04x, expected fcs = %04x ***\n", actual_fcs, expected_fcs);
#endif
}
}
#else
/*
* New way - Decode the raw bits in later step.
*/
#if TEST
text_color_set(DW_COLOR_DEBUG);
dw_printf ("\nfound flag, channel %d.%d, %d bits in frame\n", chan, subchan, rrbb_get_len(H->rrbb) - 1);
#endif
if (rrbb_get_len(H->rrbb) >= MIN_FRAME_LEN * 8) {
alevel_t alevel = demod_get_audio_level (chan, subchan);
rrbb_set_audio_level (H->rrbb, alevel);
hdlc_rec2_block (H->rrbb);
/* Now owned by someone else who will free it. */
H->rrbb = rrbb_new (chan, subchan, slice, is_scrambled, H->lfsr, H->prev_descram); /* Allocate a new one. */
}
else {
rrbb_clear (H->rrbb, is_scrambled, H->lfsr, H->prev_descram);
}
H->olen = 0; /* Allow accumulation of octets. */
H->frame_len = 0;
rrbb_append_bit (H->rrbb, H->prev_raw); /* Last bit of flag. Needed to get first data bit. */
/* Now that we are saving other initial state information, */
/* it would be sensible to do the same for this instead */
/* of lumping it in with the frame data bits. */
#endif
}
//#define EXPERIMENT12B 1
#if EXPERIMENT12B
else if (H->pat_det == 0xff) {
/*
* Valid data will never have seven 1 bits in a row.
*
* 11111110
*
* This indicates loss of signal.
* But we will let it slip thru because it might diminish
* our single bit fixup effort. Instead give up on frame
* only when we see eight 1 bits in a row.
*
* 11111111
*
* What is the impact? No difference.
*
* Before: atest -P E -F 1 ../02_Track_2.wav = 1003
* After: atest -P E -F 1 ../02_Track_2.wav = 1003
*/
#else
else if (H->pat_det == 0xfe) {
/*
* Valid data will never have 7 one bits in a row.
*
* 11111110
*
* This indicates loss of signal.
*/
#endif
H->olen = -1; /* Stop accumulating octets. */
H->frame_len = 0; /* Discard anything in progress. */
rrbb_clear (H->rrbb, is_scrambled, H->lfsr, H->prev_descram);
}
else if ( (H->pat_det & 0xfc) == 0x7c ) {
/*
* If we have five '1' bits in a row, followed by a '0' bit,
*
* 0111110xx
*
* the current '0' bit should be discarded because it was added for
* "bit stuffing."
*/
;
} else {
/*
* In all other cases, accumulate bits into octets, and complete octets
* into the frame buffer.
*/
if (H->olen >= 0) {
H->oacc >>= 1;
if (dbit) {
H->oacc |= 0x80;
}
H->olen++;
if (H->olen == 8) {
H->olen = 0;
if (H->frame_len < MAX_FRAME_LEN) {
H->frame_buf[H->frame_len] = H->oacc;
H->frame_len++;
}
}
}
}
}
/*-------------------------------------------------------------------
*
* Name: hdlc_rec_gathering
*
* Purpose: Report whether bits are currently being gathered into a frame.
* This is used to influence the PLL inertia.
* The idea is that the PLL should be a little more agreeable to
* synchronize with the incoming data stream when not in a frame
* and resist changing a little more when capturing a frame.
*
* Inputs: chan
* subchan
* slice
*
* Returns: True if we are currently gathering bits.
* In this case we want the PLL to have more inertia.
*
* Discussion: This simply returns the data carrier detect state.
* A couple other variations were tried but turned out to
* be slightly worse.
*
*--------------------------------------------------------------------*/
int hdlc_rec_gathering (int chan, int subchan, int slice)
{
assert (chan >= 0 && chan < MAX_CHANS);
assert (subchan >= 0 && subchan < MAX_SUBCHANS);
assert (slice >= 0 && slice < MAX_SLICERS);
// Counts from Track 1 & Track 2
// data_detect 992 988
// olen>=0 992 985
// OR-ed 992 985
return ( hdlc_state[chan][subchan][slice].data_detect );
} /* end hdlc_rec_gathering */
/*-------------------------------------------------------------------
*
* Name: dcd_change
*
* Purpose: Combine DCD states of all subchannels/ into an overall
* state for the channel.
*
* Inputs: chan
*
* subchan 0 to MAX_SUBCHANS-1 for HDLC.
* SPECIAL CASE --> MAX_SUBCHANS for DTMF decoder.
*
* slice slicer number, 0 .. MAX_SLICERS - 1.
*
* state 1 for active, 0 for not.
*
* Returns: None. Use hdlc_rec_data_detect_any to retrieve result.
*
* Description: DCD for the channel is active if ANY of the subchannels/slices
* are active. Update the DCD indicator.
*
* version 1.3: Add DTMF detection into the final result.
* This is now called from dtmf.c too.
*
*--------------------------------------------------------------------*/
void dcd_change (int chan, int subchan, int slice, int state)
{
int old, new;
assert (chan >= 0 && chan < MAX_CHANS);
assert (subchan >= 0 && subchan <= MAX_SUBCHANS);
assert (slice >= 0 && slice < MAX_SLICERS);
assert (state == 0 || state == 1);
#if DEBUG3
text_color_set(DW_COLOR_DEBUG);
dw_printf ("DCD %d.%d.%d = %d \n", chan, subchan, slice, state);
#endif
old = hdlc_rec_data_detect_any(chan);
if (state) {
composite_dcd[chan][subchan] |= (1 << slice);
}
else {
composite_dcd[chan][subchan] &= ~ (1 << slice);
}
new = hdlc_rec_data_detect_any(chan);
if (new != old) {
ptt_set (OCTYPE_DCD, chan, new);
}
}
/*-------------------------------------------------------------------
*
* Name: hdlc_rec_data_detect_any
*
* Purpose: Determine if the radio channel is curently busy
* with packet data.
* This version doesn't care about voice or other sounds.
* This is used by the transmit logic to transmit only
* when the channel is clear.
*
* Inputs: chan - Audio channel.
*
* Returns: True if channel is busy (data detected) or
* false if OK to transmit.
*
*
* Description: We have two different versions here.
*
* hdlc_rec_data_detect_any sees if ANY of the decoders
* for this channel are receving a signal. This is
* used to determine whether the channel is clear and
* we can transmit. This would apply to the 300 baud
* HF SSB case where we have multiple decoders running
* at the same time. The channel is busy if ANY of them
* thinks the channel is busy.
*
* Version 1.3: New option for input signal to inhibit transmit.
*
*--------------------------------------------------------------------*/
int hdlc_rec_data_detect_any (int chan)
{
int sc;
assert (chan >= 0 && chan < MAX_CHANS);
for (sc = 0; sc < num_subchan[chan]; sc++) {
if (composite_dcd[chan][sc] != 0)
return (1);
}
if (get_input(ICTYPE_TXINH, chan) == 1) return (1);
return (0);
} /* end hdlc_rec_data_detect_any */
/* end hdlc_rec.c */
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