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direwolf/src/il2p_codec.c

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//
// This file is part of Dire Wolf, an amateur radio packet TNC.
//
// Copyright (C) 2021 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/>.
//
#include "direwolf.h"
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
#include <string.h>
#include "il2p.h"
#include "textcolor.h"
#include "demod.h"
/*-------------------------------------------------------------
*
* File: il2p_codec.c
*
* Purpose: Convert IL2P encoded format from and to direwolf internal packet format.
*
*--------------------------------------------------------------*/
/*-------------------------------------------------------------
*
* Name: il2p_encode_frame
*
* Purpose: Convert AX.25 frame to IL2P encoding.
*
* Inputs: chan - Audio channel number, 0 = first.
*
* pp - Packet object pointer.
*
* max_fec - 1 to send maximum FEC size rather than automatic.
*
* Outputs: iout - Encoded result, excluding the 3 byte sync word.
* Caller should provide IL2P_MAX_PACKET_SIZE bytes.
*
* Returns: Number of bytes for transmission.
* -1 is returned for failure.
*
* Description: Encode into IL2P format.
*
* Errors: If something goes wrong, return -1.
*
* Most likely reason is that the frame is too large.
* IL2P has a max payload size of 1023 bytes.
* For a type 1 header, this is the maximum AX.25 Information part size.
* For a type 0 header, this is the entire AX.25 frame.
*
*--------------------------------------------------------------*/
int il2p_encode_frame (packet_t pp, int max_fec, unsigned char *iout)
{
// Can a type 1 header be used?
unsigned char hdr[IL2P_HEADER_SIZE + IL2P_HEADER_PARITY];
int e;
int out_len = 0;
e = il2p_type_1_header (pp, max_fec, hdr);
if (e >= 0) {
il2p_scramble_block (hdr, iout, IL2P_HEADER_SIZE);
il2p_encode_rs (iout, IL2P_HEADER_SIZE, IL2P_HEADER_PARITY, iout+IL2P_HEADER_SIZE);
out_len = IL2P_HEADER_SIZE + IL2P_HEADER_PARITY;
if (e == 0) {
// Success. No info part.
return (out_len);
}
// Payload is AX.25 info part.
unsigned char *pinfo;
int info_len;
info_len = ax25_get_info (pp, &pinfo);
int k = il2p_encode_payload (pinfo, info_len, max_fec, iout+out_len);
if (k > 0) {
out_len += k;
// Success. Info part was <= 1023 bytes.
return (out_len);
}
// Something went wrong with the payload encoding.
return (-1);
}
else if (e == -1) {
// Could not use type 1 header for some reason.
// e.g. More than 2 addresses, extended (mod 128) sequence numbers, etc.
e = il2p_type_0_header (pp, max_fec, hdr);
if (e > 0) {
il2p_scramble_block (hdr, iout, IL2P_HEADER_SIZE);
il2p_encode_rs (iout, IL2P_HEADER_SIZE, IL2P_HEADER_PARITY, iout+IL2P_HEADER_SIZE);
out_len = IL2P_HEADER_SIZE + IL2P_HEADER_PARITY;
// Payload is entire AX.25 frame.
unsigned char *frame_data_ptr = ax25_get_frame_data_ptr (pp);
int frame_len = ax25_get_frame_len (pp);
int k = il2p_encode_payload (frame_data_ptr, frame_len, max_fec, iout+out_len);
if (k > 0) {
out_len += k;
// Success. Entire AX.25 frame <= 1023 bytes.
return (out_len);
}
// Something went wrong with the payload encoding.
return (-1);
}
else if (e == 0) {
// Impossible condition. Type 0 header must have payload.
return (-1);
}
else {
// AX.25 frame is too large.
return (-1);
}
}
// AX.25 Information part is too large.
return (-1);
}
/*-------------------------------------------------------------
*
* Name: il2p_decode_frame
*
* Purpose: Convert IL2P encoding to AX.25 frame.
* This is only used during testing, with a whole encoded frame.
* During reception, the header would have FEC and descrambling
* applied first so we would know how much to collect for the payload.
*
* Inputs: irec - Received IL2P frame excluding the 3 byte sync word.
*
* Future Out: Number of symbols corrected.
*
* Returns: Packet pointer or NULL for error.
*
*--------------------------------------------------------------*/
packet_t il2p_decode_frame (unsigned char *irec)
{
unsigned char uhdr[IL2P_HEADER_SIZE]; // After FEC and descrambling.
int e = il2p_clarify_header (irec, uhdr);
// TODO?: for symmetry we might want to clarify the payload before combining.
return (il2p_decode_header_payload(uhdr, irec + IL2P_HEADER_SIZE + IL2P_HEADER_PARITY, &e));
}
/*-------------------------------------------------------------
*
* Name: il2p_decode_header_payload
*
* Purpose: Convert IL2P encoding to AX.25 frame
*
* Inputs: uhdr - Received header after FEC and descrambling.
* epayload - Encoded payload.
*
* In/Out: symbols_corrected - Symbols (bytes) corrected in the header.
* Should be 0 or 1 because it has 2 parity symbols.
* Here we add number of corrections for the payload.
*
* Returns: Packet pointer or NULL for error.
*
*--------------------------------------------------------------*/
packet_t il2p_decode_header_payload (unsigned char* uhdr, unsigned char *epayload, int *symbols_corrected)
{
int hdr_type;
int max_fec;
int payload_len = il2p_get_header_attributes (uhdr, &hdr_type, &max_fec);
packet_t pp = NULL;
if (hdr_type == 1) {
// Header type 1. Any payload is the AX.25 Information part.
pp = il2p_decode_header_type_1 (uhdr, *symbols_corrected);
if (pp == NULL) {
// Failed for some reason.
return (NULL);
}
if (payload_len > 0) {
// This is the AX.25 Information part.
unsigned char extracted[IL2P_MAX_PAYLOAD_SIZE];
int e = il2p_decode_payload (epayload, payload_len, max_fec, extracted, symbols_corrected);
// It would be possible to have a good header but too many errors in the payload.
if (e <= 0) {
ax25_delete (pp);
pp = NULL;
return (pp);
}
if (e != payload_len) {
text_color_set(DW_COLOR_ERROR);
dw_printf ("IL2P Internal Error: %s(): hdr_type=%d, max_fec=%d, payload_len=%d, e=%d.\n", __func__, hdr_type, max_fec, payload_len, e);
}
ax25_set_info (pp, extracted, payload_len);
}
return (pp);
}
else {
// Header type 0. The payload is the entire AX.25 frame.
unsigned char extracted[IL2P_MAX_PAYLOAD_SIZE];
int e = il2p_decode_payload (epayload, payload_len, max_fec, extracted, symbols_corrected);
if (e <= 0) { // Payload was not received correctly.
return (NULL);
}
if (e != payload_len) {
text_color_set(DW_COLOR_ERROR);
dw_printf ("IL2P Internal Error: %s(): hdr_type=%d, e=%d, payload_len=%d\n", __func__, hdr_type, e, payload_len);
return (NULL);
}
alevel_t alevel;
memset (&alevel, 0, sizeof(alevel));
//alevel = demod_get_audio_level (chan, subchan); // What TODO? We don't know channel here.
// I think alevel gets filled in somewhere later making
// this redundant.
pp = ax25_from_frame (extracted, payload_len, alevel);
return (pp);
}
} // end il2p_decode_header_payload
// end il2p_codec.c
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