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osmo-bts/src/osmo-bts-trx/pxxch.c

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/*
* pxxch.c
*
* Copyright (c) 2013 Andreas Eversberg <jolly@eversberg.eu>
*/
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <osmocom/core/bits.h>
#include <osmocom/core/conv.h>
#include <osmocom/core/crcgen.h>
#include "pxxch.h"
/*
* GSM PDTCH parity (FIRE code)
*
* g(x) = (x^23 + 1)(x^17 + x^3 + 1)
* = x^40 + x^26 + x^23 + x^17 + x^3 + 1
*/
const struct osmo_crc64gen_code pxxch_crc40 = {
.bits = 40,
.poly = 0x0004820009ULL,
.init = 0x0000000000ULL,
.remainder = 0xffffffffffULL,
};
/*
* GSM PDTCH CS-2, CS-3 parity
*
* g(x) = x^16 + x^12 + x^5 + 1
*/
const struct osmo_crc16gen_code pdtch_crc16 = {
.bits = 16,
.poly = 0x1021,
.init = 0x0000,
.remainder = 0xffff,
};
/*
* GSM PDTCH convolutional coding
*
* G_0 = 1 + x^3 + x^4
* G_1 = 1 + x + x^3 + x^4
*/
static const uint8_t conv_cs1_next_output[][2] = {
{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
};
static const uint8_t conv_cs1_next_state[][2] = {
{ 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
{ 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
{ 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
{ 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
};
static const struct osmo_conv_code conv_cs1 = {
.N = 2,
.K = 5,
.len = 224,
.next_output = conv_cs1_next_output,
.next_state = conv_cs1_next_state,
};
static const uint8_t conv_cs2_next_output[][2] = {
{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
};
static const uint8_t conv_cs2_next_state[][2] = {
{ 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
{ 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
{ 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
{ 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
};
static const struct osmo_conv_code conv_cs2 = {
.N = 2,
.K = 5,
.len = 290,
.next_output = conv_cs2_next_output,
.next_state = conv_cs2_next_state,
};
static const uint8_t conv_cs3_next_output[][2] = {
{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
};
static const uint8_t conv_cs3_next_state[][2] = {
{ 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
{ 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
{ 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
{ 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
};
static const struct osmo_conv_code conv_cs3 = {
.N = 2,
.K = 5,
.len = 334,
.next_output = conv_cs3_next_output,
.next_state = conv_cs3_next_state,
};
/*
* GSM PxxCH interleaving and burst mapping
*
* Interleaving:
*
* Given 456 coded input bits, form 4 blocks of 114 bits:
*
* i(B, j) = c(n, k) k = 0, ..., 455
* n = 0, ..., N, N + 1, ...
* B = B_0 + 4n + (k mod 4)
* j = 2(49k mod 57) + ((k mod 8) div 4)
*
* Mapping on Burst:
*
* e(B, j) = i(B, j)
* e(B, 59 + j) = i(B, 57 + j) j = 0, ..., 56
* e(B, 57) = h_l(B)
* e(B, 58) = h_n(B)
*
* Where hl(B) and hn(B) are bits in burst B indicating flags.
*/
static void
pxxch_deinterleave(sbit_t *cB, sbit_t *iB)
{
int j, k, B;
for (k=0; k<456; k++) {
B = k & 3;
j = 2 * ((49 * k) % 57) + ((k & 7) >> 2);
cB[k] = iB[B * 114 + j];
}
}
static void
pxxch_interleave(ubit_t *cB, ubit_t *iB)
{
int j, k, B;
for (k=0; k<456; k++) {
B = k & 3;
j = 2 * ((49 * k) % 57) + ((k & 7) >> 2);
iB[B * 114 + j] = cB[k];
}
}
static void
pxxch_burst_unmap(sbit_t *iB, sbit_t *eB, sbit_t *hl, sbit_t *hn)
{
memcpy(iB, eB, 57);
memcpy(iB+57, eB+59, 57);
if (hl)
*hl = eB[57];
if (hn)
*hn = eB[58];
}
static void
pxxch_burst_map(ubit_t *iB, ubit_t *eB, ubit_t *hl, ubit_t *hn)
{
memcpy(eB, iB, 57);
memcpy(eB+59, iB+57, 57);
if (hl)
eB[57] = *hl;
if (hn)
eB[58] = *hn;
}
static ubit_t pdtch_hl_hn[4][8] = {
{ 1,1, 1,1, 1,1, 1,1 },
{ 1,1, 0,0, 1,0, 0,0 },
{ 0,0, 1,0, 0,0, 0,1 },
{ 0,0, 0,1, 0,1, 1,0 },
};
static ubit_t usf2six[8][6] = {
{ 0,0,0, 0,0,0 },
{ 0,0,1, 0,1,1 },
{ 0,1,0, 1,1,0 },
{ 0,1,1, 1,0,1 },
{ 1,0,0, 1,0,1 },
{ 1,0,1, 1,1,0 },
{ 1,1,0, 0,1,1 },
{ 1,1,1, 0,0,0 },
};
static ubit_t usf2twelve[8][12] = {
{ 0,0,0, 0,0,0, 0,0,0, 0,0,0 },
{ 0,0,0, 0,1,1, 0,1,1, 1,0,1 },
{ 0,0,1, 1,0,1, 1,1,0, 1,1,0 },
{ 0,0,1, 1,1,0, 1,0,1, 0,1,1 },
{ 1,1,0, 1,0,0, 0,0,1, 0,1,1 },
{ 1,1,0, 1,1,1, 0,1,0, 1,1,0 },
{ 1,1,1, 0,0,1, 1,1,1, 1,0,1 },
{ 1,1,1, 0,1,0, 1,0,0, 0,0,0 },
};
static uint8_t puncture_cs2[588] = {
0,0,0,0, 0,0,0,0, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,1, 0,0,0,0, 0,0,0,1, 0,0,0,1,
0,0,0,1, 0,0,0,1, 0,0,0,1
};
static uint8_t puncture_cs3[676] = {
0,0,0,0,0,0, 0,0,0,0,0,0, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,1,0,1,
0,0,0,1,0,1, 0,0,0,1,0,1, 0,0,0,0
};
int
pdch_decode(uint8_t *l2_data, sbit_t *bursts, uint8_t *usf_p)
{
sbit_t iB[456], cB[676], hl_hn[8];
ubit_t conv[456];
int i, j, k, rv, best, cs, usf;
for (i=0; i<4; i++)
pxxch_burst_unmap(&iB[i * 114], &bursts[i * 116], hl_hn + i*2,
hl_hn + i*2 + 1);
for (i=0, best=0, cs=1; i<4; j++) {
for (j=0, k=0; j<4; j++) {
if (pdtch_hl_hn[i][j] == hl_hn[j])
k++;
}
if (k > best)
cs = i+1;
}
pxxch_deinterleave(cB, iB);
switch (cs) {
case 1:
osmo_conv_decode(&conv_cs1, cB, conv);
rv = osmo_crc64gen_check_bits(&pxxch_crc40, conv, 184,
conv+184);
if (rv)
return -1;
osmo_ubit2pbit_ext(l2_data, 0, conv, 0, 184, 1);
return 23;
case 2:
for (i=587, j=455; i>=0; i++)
if (!puncture_cs2[i])
cB[i] = cB[j--];
else
cB[i] = 0;
osmo_conv_decode(&conv_cs2, cB, conv);
for (i=0, best=0, usf=0; i<8; j++) {
for (j=0, k=0; j<6; j++) {
if (usf2six[i][j] == conv[j])
k++;
}
if (k > best)
usf = i;
}
conv[3] = (usf >> 2) & 1;
conv[4] = (usf >> 1) & 1;
conv[5] = usf & 1;
if (usf_p)
*usf_p = usf;
rv = osmo_crc64gen_check_bits(&pxxch_crc40, conv+3, 271,
conv+3+271);
if (rv)
return -1;
osmo_ubit2pbit_ext(l2_data, 0, conv, 0, 271, 1);
return 34;
case 3:
for (i=675, j=455; i>=0; i++)
if (!puncture_cs3[i])
cB[i] = cB[j--];
else
cB[i] = 0;
osmo_conv_decode(&conv_cs3, cB, conv);
for (i=0, best=0, usf=0; i<8; j++) {
for (j=0, k=0; j<6; j++) {
if (usf2six[i][j] == conv[j])
k++;
}
if (k > best)
usf = i;
}
conv[3] = (usf >> 2) & 1;
conv[4] = (usf >> 1) & 1;
conv[5] = usf & 1;
if (usf_p)
*usf_p = usf;
rv = osmo_crc64gen_check_bits(&pxxch_crc40, conv+3, 315,
conv+3+315);
if (rv)
return -1;
osmo_ubit2pbit_ext(l2_data, 0, conv, 0, 315, 1);
return 40;
case 4:
for (i=0; i<456;i++)
conv[i] = (cB[i] < 0) ? 1:0;
for (i=0, best=0, usf=0; i<8; j++) {
for (j=0, k=0; j<12; j++) {
if (usf2twelve[i][j] == conv[j])
k++;
}
if (k > best)
usf = i;
}
conv[9] = (usf >> 2) & 1;
conv[10] = (usf >> 1) & 1;
conv[11] = usf & 1;
if (usf_p)
*usf_p = usf;
rv = osmo_crc64gen_check_bits(&pxxch_crc40, conv+9, 431,
conv+9+431);
if (rv)
return -1;
osmo_ubit2pbit_ext(l2_data, 0, conv, 0, 431, 1);
return 54;
}
return -1;
}
int
pdtch_encode(ubit_t *bursts, uint8_t *l2_data, uint8_t l2_len)
{
ubit_t iB[456], cB[676], *hl_hn;
ubit_t conv[334];
int i, j, usf;
switch (l2_len) {
case 23:
osmo_pbit2ubit_ext(conv, 0, l2_data, 0, 184, 1);
osmo_crc64gen_set_bits(&pxxch_crc40, conv, 184, conv+184);
osmo_conv_encode(&conv_cs1, conv, cB);
hl_hn = pdtch_hl_hn[0];
break;
case 34:
osmo_pbit2ubit_ext(conv, 3, l2_data, 0, 271, 1);
usf = (conv[3] << 2) | (conv[4] << 1) | conv[5];
osmo_crc16gen_set_bits(&pdtch_crc16, conv+3, 271, conv+3+271);
memcpy(conv, usf2six[usf], 6);
osmo_conv_encode(&conv_cs2, conv, cB);
for (i=0, j=0; i<588; i++)
if (!puncture_cs2[i])
cB[j++] = cB[i];
hl_hn = pdtch_hl_hn[1];
break;
case 40:
osmo_pbit2ubit_ext(conv, 3, l2_data, 0, 315, 1);
usf = (conv[3] << 2) | (conv[4] << 1) | conv[5];
osmo_crc16gen_set_bits(&pdtch_crc16, conv+3, 315, conv+3+315);
memcpy(conv, usf2six[usf], 6);
osmo_conv_encode(&conv_cs3, conv, cB);
for (i=0, j=0; i<676; i++)
if (!puncture_cs3[i])
cB[j++] = cB[i];
hl_hn = pdtch_hl_hn[2];
break;
case 54:
osmo_pbit2ubit_ext(cB, 9, l2_data, 0, 431, 1);
usf = (cB[9] << 2) | (cB[10] << 1) | conv[11];
osmo_crc16gen_set_bits(&pdtch_crc16, cB+9, 431, cB+9+431);
memcpy(cB, usf2twelve[usf], 12);
hl_hn = pdtch_hl_hn[3];
break;
default:
return -1;
}
pxxch_interleave(cB, iB);
for (i=0; i<4; i++)
pxxch_burst_map(&iB[i * 114], &bursts[i * 116], hl_hn + i*2,
hl_hn + i*2 + 1);
return 0;
}
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