Osmocom GSM/GPRS/EGPRS transceiver, originally forked from OpenBTS transceiver. For building SDR based GSM BTS with osmo-bts-trx.
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/* Dummy TRX for sening PRBS test sequences into osmo-bts-trx to test
* the decoder/receiver processing in osmo-bts-trx as well as any
* additional PRBS testing code.
*
* The purpose of this program is to use it as a mock dummy MS-side
* transmitter of GSM bursts that contain encoded PRBS sequences,
* similar to what one would normally do with an arbitrary
* function/waveform generator or BERT tester in hardware.
*
* (C) 2017 by Harald Welte <laforge@gnumonks.org>
* All Rights Reserved
*
* Licensed under terms of the GNU Generral Public License, Version 2,
* or (at your option) any later version.
*/
#include <stdint.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
#include <unistd.h>
#include <netinet/in.h>
#include <osmocom/core/bits.h>
#include <osmocom/core/utils.h>
#include <osmocom/core/prbs.h>
#include <osmocom/core/socket.h>
#include <osmocom/gsm/gsm_utils.h>
#include <osmocom/coding/gsm0503_coding.h>
/***********************************************************************
* GSM Constants
***********************************************************************/
#define GSM_FR_BYTES 33
#define GSM_BURST_BITS 116
#define GSM_4BURST_BITS (GSM_BURST_BITS*4)
#define GSM_BURST_LEN 148
/***********************************************************************
* TRX Interface / Protocol
***********************************************************************/
#define TRX_BASE_PORT 5700
/* DATA port on the TRX side */
#define TRX_PORT_CTRL_TRX(C) (TRX_BASE_PORT+(2*(C))+1)
#define TRX_PORT_DATA_TRX(C) (TRX_BASE_PORT+(2*(C))+2)
#define TRX_PORT_CTRL_BTS(C) (TRX_PORT_CTRL_TRX(C)+100)
#define TRX_PORT_DATA_BTS(C) (TRX_PORT_DATA_TRX(C)+100)
struct trx_ul_msg {
uint8_t ts;
uint32_t fn;
uint8_t rssi;
uint16_t t_offs;
uint8_t bits[148]; /* 0..255, *NOT* sbit_t */
} __attribute__((packed));
struct trx_dl_msg {
uint8_t ts;
uint32_t fn;
uint8_t att_db;
ubit_t bits[148];
} __attribute__((packed));
/***********************************************************************
* Helper Functions
***********************************************************************/
static int ubits2trxbits(uint8_t *sbits, const ubit_t *ubits, unsigned int count)
{
unsigned int i;
for (i = 0; i < count; i++) {
if ((*ubits++) & 1) {
*sbits++ = 255;
} else {
*sbits++ = 0;
}
}
return count;
}
static int __attribute__((__unused__)) dec(const ubit_t *bursts_u)
{
sbit_t bursts_s[GSM_4BURST_BITS*2];
uint8_t dec_tch_data[GSM_FR_BYTES];
int n_errors, n_bits_total;
int rc;
/* convert from u_bit (tx) to s_bit (rx) */
osmo_ubit2sbit(bursts_s, bursts_u, sizeof(bursts_s));
rc = gsm0503_tch_fr_decode(dec_tch_data, bursts_s, 1, 0, &n_errors, &n_bits_total);
printf("rc=%d, n_errors=%d, n_bits_total=%d: %s\n", rc, n_errors, n_bits_total,
osmo_hexdump(dec_tch_data, sizeof(dec_tch_data)));
return rc;
}
/*! \brief Training Sequences (TS 05.02 Chapter 5.2.3) */
static const ubit_t _sched_tsc[8][26] = {
{ 0,0,1,0,0,1,0,1,1,1,0,0,0,0,1,0,0,0,1,0,0,1,0,1,1,1, },
{ 0,0,1,0,1,1,0,1,1,1,0,1,1,1,1,0,0,0,1,0,1,1,0,1,1,1, },
{ 0,1,0,0,0,0,1,1,1,0,1,1,1,0,1,0,0,1,0,0,0,0,1,1,1,0, },
{ 0,1,0,0,0,1,1,1,1,0,1,1,0,1,0,0,0,1,0,0,0,1,1,1,1,0, },
{ 0,0,0,1,1,0,1,0,1,1,1,0,0,1,0,0,0,0,0,1,1,0,1,0,1,1, },
{ 0,1,0,0,1,1,1,0,1,0,1,1,0,0,0,0,0,1,0,0,1,1,1,0,1,0, },
{ 1,0,1,0,0,1,1,1,1,1,0,1,1,0,0,0,1,0,1,0,0,1,1,1,1,1, },
{ 1,1,1,0,1,1,1,1,0,0,0,1,0,0,1,0,1,1,1,0,1,1,1,1,0,0, },
};
/***********************************************************************
* state + processing functions
***********************************************************************/
/* state we have to keep for one physical channel */
struct pchan_data {
/* PRBS state */
struct osmo_prbs_state st;
/* unpacked PRBS bits, generated from PRBS */
ubit_t prbs_u[4+260];
/* packed frame (to be sent) */
uint8_t tch_data[GSM_FR_BYTES];
/* burst bits (ubit) to be transmitted */
ubit_t bursts[GSM_4BURST_BITS*2]; /* 116 * 8 */
/* burst bits (sbit) 'as if received' */
sbit_t bursts_s[GSM_4BURST_BITS*2];
/* next to-be transmitted burst number */
unsigned int burst_nr;
/* training sequence code */
unsigned int tsc;
/* loose 'count' bursts every 'nth_mframe' on TRX-BTS interface */
struct {
unsigned int count;
unsigned int nth_mframe;
} sim_lost_bursts;
/* zero 'count' bursts every 'nth_mframe' on TRX-BTS interface */
struct {
unsigned int count;
unsigned int nth_mframe;
} sim_zero_bursts;
/* flip every 'nth_bit' of the PRNG oudput before encoding */
struct {
unsigned int nth_bit;
unsigned int i;
} sim_flip_codec_bits;
unsigned int i;
};
struct ts_data {
struct pchan_data pchan[2];
};
struct trx_data {
struct ts_data ts[8];
};
static struct trx_data g_trx_data;
/* initialize the state for one TRX */
static void trx_data_init(struct trx_data *trx)
{
int i;
for (i = 0; i < ARRAY_SIZE(trx->ts); i++) {
struct ts_data *ts = &trx->ts[i];
int j;
for (j = 0; j < ARRAY_SIZE(ts->pchan); j++) {
struct pchan_data *pchan = &ts->pchan[j];
memset(pchan, 0, sizeof(*pchan));
osmo_prbs_state_init(&pchan->st, &osmo_prbs9);
pchan->tsc = 7;
}
}
}
/* apply any intentional errors to the output of the PRBS sequence */
static void apply_errors_prbs(struct pchan_data *pchan)
{
int i;
for (i = 0; i < sizeof(pchan->prbs_u)-4; i++) {
pchan->sim_flip_codec_bits.i++;
if (pchan->sim_flip_codec_bits.i == pchan->sim_flip_codec_bits.nth_bit) {
pchan->sim_flip_codec_bits.i = 0;
pchan->prbs_u[4+i] ^= 0x01;
}
}
}
/*! obtain the next to-be-transmitted burst for the given pchan
* \param pchan physical channel on which we operate
* \param[in] fn frame number
* \param[out] burst_out caller-provided buffer for 148 unpacked output bits
* \retruns number of bits stored in \a burst_out */
static int pchan_get_next_burst(struct pchan_data *pchan, uint32_t fn, ubit_t *burst_out)
{
uint32_t fn26 = fn % 26;
int rc;
if (fn26 == 0 || fn26 == 4 || fn26 == 8 || fn26 == 13 || fn26 == 17 || fn26 == 21)
pchan->burst_nr = 0;
if (fn26 == 12 || fn26 == 25) {
memset(burst_out, 0, GSM_BURST_LEN);
return GSM_BURST_LEN;
}
if (pchan->burst_nr == 0) {
/* generate PRBS output in ubit format, skipping first nibble for 260-264 padding */
const uint8_t prefix[] = { 0xd0 };
osmo_pbit2ubit(pchan->prbs_u, prefix, 4);
rc = osmo_prbs_get_ubits(pchan->prbs_u+4, sizeof(pchan->prbs_u)-4, &pchan->st);
OSMO_ASSERT(rc == sizeof(pchan->prbs_u)-4);
apply_errors_prbs(pchan);
/* pack to PBIT format */
rc = osmo_ubit2pbit(pchan->tch_data, pchan->prbs_u, sizeof(pchan->prbs_u));
//memset(pchan->tch_data, 0xff, sizeof(pchan->tch_data));
printf("%s\n", osmo_hexdump(pchan->tch_data, GSM_FR_BYTES));
/* shift buffer by 4 bursts for interleaving */
memcpy(pchan->bursts, pchan->bursts + GSM_4BURST_BITS, GSM_4BURST_BITS);
memset(pchan->bursts + GSM_4BURST_BITS, 0, GSM_4BURST_BITS);
/* encode block (codec frame) into four bursts */
rc = gsm0503_tch_fr_encode(pchan->bursts, pchan->tch_data, GSM_FR_BYTES, 1);
OSMO_ASSERT(rc == 0);
#if 0
int i;
for (i = 0; i < sizeof(pchan->bursts); i += GSM_BURST_BITS)
printf("\t%s\n", osmo_ubit_dump(pchan->bursts + i, GSM_BURST_BITS));
dec(pchan->bursts);
#endif
}
/* for all bursts: format 148 symbols from 116 input bits */
ubit_t *burst = pchan->bursts + pchan->burst_nr * GSM_BURST_BITS;
// printf("TX(%u): %s\n", pchan->burst_nr, osmo_ubit_dump(burst, GSM_BURST_BITS));
memset(burst_out, 0, 3); /* guard bits */
memcpy(burst_out+3, burst, 58); /* firrst half */
memcpy(burst_out+61, _sched_tsc[pchan->tsc], 26); /* midamble */
memcpy(burst_out+87, burst+58, 58); /* second half */
memset(burst_out+145, 0, 3); /* guard bits */
/* increment burst number for next call */
pchan->burst_nr += 1;
return GSM_BURST_LEN;
}
static int pchan_process_ts_fn(struct pchan_data *pchan, uint32_t fn, uint8_t *burst_t)
{
ubit_t burst_u[GSM_BURST_LEN];
int rc;
rc = pchan_get_next_burst(pchan, fn, burst_u);
OSMO_ASSERT(rc == sizeof(burst_u));
/* convert from u_bit (tx) to s_bit (rx) */
ubits2trxbits(burst_t, burst_u, GSM_BURST_LEN);
return GSM_BURST_LEN;
}
/* read TRX DL data from BTS, write TRX UL data to BTS */
static int read_and_process(int fd)
{
/* receive (downlink) buffer */
uint8_t rx_dl_buf[1024];
struct trx_dl_msg *dl_msg = (struct trx_dl_msg *) rx_dl_buf;
/* transmit (uplink) buffer */
uint8_t tx_ul_buf[1024];
struct trx_ul_msg *ul_msg = (struct trx_ul_msg *) tx_ul_buf;
/* other variables */
struct pchan_data *pchan;
uint32_t fn;
uint8_t rc;
/* do a blocking read on the socket and receive DL from BTS */
rc = read(fd, rx_dl_buf, sizeof(rx_dl_buf));
if (rc < sizeof(*dl_msg))
return rc;
fn = ntohl(dl_msg->fn);
if (dl_msg->ts >= ARRAY_SIZE(g_trx_data.ts))
return -ENODEV;
if (dl_msg->ts != 2)
return 0;
printf("FN=%s TS=%u\n", gsm_fn_as_gsmtime_str(fn), dl_msg->ts);
/* FIXME: second pchan for TCH/H */
pchan = &g_trx_data.ts[dl_msg->ts].pchan[0];
rc = pchan_process_ts_fn(pchan, fn, (uint8_t *) ul_msg->bits);
OSMO_ASSERT(rc == sizeof(ul_msg->bits));
/* copy over timeslot and frame number */
ul_msg->fn = htonl(fn);
ul_msg->ts = dl_msg->ts;
/* simulate lost frames on TRX <-> BTS interface */
if (pchan->sim_lost_bursts.count) {
/* count number of 26-multiframes */
static int count = 0;
if (fn % 26 == 0)
count++;
/* every 10th multiframe, drop two entire block of 8 bursts */
if (count % pchan->sim_lost_bursts.nth_mframe == 0 &&
(fn % 26) <= pchan->sim_lost_bursts.count) {
printf("===> SKIPPING BURST\n");
return 0;
}
}
/* simulate zero-ed frames on TRX <-> BTS interface */
if (pchan->sim_zero_bursts.count) {
/* count number of 26-multiframes */
static int count = 0;
if (fn % 26 == 0)
count++;
/* every 10th multiframe, drop two entire block of 8 bursts */
if (count % pchan->sim_zero_bursts.nth_mframe == 0 &&
(fn % 26) <= pchan->sim_zero_bursts.count) {
memset(ul_msg->bits, 0, sizeof(ul_msg->bits));
printf("===> ZEROING BURST\n");
}
}
/* write uplink message towards BTS */
rc = write(fd, tx_ul_buf, sizeof(*ul_msg));
if (rc < sizeof(*ul_msg))
return -EIO;
return 0;
}
static int open_trx_data_sock(unsigned int trx_nr, const char *bts_host)
{
int rc;
rc = osmo_sock_init2(AF_INET, SOCK_DGRAM, IPPROTO_UDP, NULL, TRX_PORT_DATA_TRX(trx_nr),
bts_host, TRX_PORT_DATA_BTS(trx_nr),
OSMO_SOCK_F_CONNECT | OSMO_SOCK_F_BIND);
return rc;
}
int main(int argc, char **argv)
{
int fd;
trx_data_init(&g_trx_data);
//g_trx_data.ts[2].pchan[0].sim_zero_bursts.count = 8;
//g_trx_data.ts[2].pchan[0].sim_zero_bursts.nth_mframe = 10;
g_trx_data.ts[2].pchan[0].sim_flip_codec_bits.nth_bit = 260*4;
fd = open_trx_data_sock(0, "127.0.0.1");
if (fd < 0)
exit(1);
while (1) {
read_and_process(fd);
}
return 0;
}