/* *      pocsag.c -- POCSAG protocol decoder * *      Copyright (C) 1996   *          Thomas Sailer (sailer@ife.ee.ethz.ch, hb9jnx@hb9w.che.eu) * *      POCSAG (Post Office Code Standard Advisory Group) *      Radio Paging Decoder * *	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, write to the Free Software *	Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. *//* ---------------------------------------------------------------------- */#include "multimon.h"#include <string.h>/* ---------------------------------------------------------------------- */#define CHARSET_LATIN1/* ---------------------------------------------------------------------- *//* * the code used by POCSAG is a (n=31,k=21) BCH Code with dmin=5, * thus it could correct two bit errors in a 31-Bit codeword. * It is a systematic code. * The generator polynomial is:  *   g(x) = x^10+x^9+x^8+x^6+x^5+x^3+1 * The parity check polynomial is:  *   h(x) = x^21+x^20+x^18+x^16+x^14+x^13+x^12+x^11+x^8+x^5+x^3+1 * g(x) * h(x) = x^n+1 */#define BCH_POLY 03551 /* octal */#define BCH_N    31#define BCH_K    21/* * some codewords with special POCSAG meaning */#define POCSAG_SYNC     0x7cd215d8#define POCSAG_SYNCINFO 0x7cf21436#define POCSAG_IDLE     0x7a89c197#define POCSAG_SYNC_WORDS ((2000000 >> 3) << 13)/* ---------------------------------------------------------------------- */static unsigned char service_mask = 0x87;/* ---------------------------------------------------------------------- */static inline unsigned char even_parity(unsigned long data) {	unsigned int temp = data ^ (data >> 16);		temp = temp ^ (temp >> 8);	temp = temp ^ (temp >> 4);	temp = temp ^ (temp >> 2);	temp = temp ^ (temp >> 1);	return temp & 1;}/* ---------------------------------------------------------------------- */static unsigned long pocsag_code(unsigned long data) {	unsigned long ret = data << (BCH_N-BCH_K), shreg = ret;	unsigned long mask = 1L << (BCH_N-1), coeff = BCH_POLY << (BCH_K-1);	int n = BCH_K;		for(; n > 0; mask >>= 1, coeff >>= 1, n--)		if (shreg & mask)			shreg ^= coeff;	ret ^= shreg;	ret = (ret << 1) | even_parity(ret);	verbprintf(9, "BCH coder: data: %08lx shreg: %08lx ret: %08lx\n", 		   data, shreg, ret);	return ret;}/* ---------------------------------------------------------------------- */static unsigned int pocsag_syndrome(unsigned long data) {	unsigned long shreg = data >> 1; /* throw away parity bit */	unsigned long mask = 1L << (BCH_N-1), coeff = BCH_POLY << (BCH_K-1);	int n = BCH_K;		for(; n > 0; mask >>= 1, coeff >>= 1, n--)		if (shreg & mask)			shreg ^= coeff;	if (even_parity(data))		shreg |= (1 << (BCH_N - BCH_K));	verbprintf(9, "BCH syndrome: data: %08lx syn: %08lx\n", data, shreg);	return shreg;}/* ---------------------------------------------------------------------- */static void print_msg_numeric(struct l2_pocsag_rx *rx) {	static const char *conv_table = "084 2.6]195-3U7[";	unsigned char *bp = rx->buffer;	int len = rx->numnibbles;	char buf[256], *cp = buf;       	if (len >= sizeof(buf)) 		len = sizeof(buf)-1;	for (; len > 0; bp++, len -= 2) {		*cp++ = conv_table[(*bp >> 4) & 0xf];		if (len > 1)			*cp++ = conv_table[*bp & 0xf];	}	*cp = '\0';	verbprintf(0, "%s\n", buf);}/* ---------------------------------------------------------------------- */static char *translate_alpha(unsigned char chr) {	static const struct trtab {		unsigned char code;		char *str;	} trtab[] = {{  0, "<NUL>" },		     {  1, "<SOH>" }, 		     {  2, "<STX>" }, 		     {  3, "<ETX>" }, 		     {  4, "<EOT>" }, 		     {  5, "<ENQ>" }, 		     {  6, "<ACK>" }, 		     {  7, "<BEL>" }, 		     {  8, "<BS>" }, 		     {  9, "<HT>" }, 		     { 10, "<LF>" }, 		     { 11, "<VT>" }, 		     { 12, "<FF>" }, 		     { 13, "<CR>" }, 		     { 14, "<SO>" }, 		     { 15, "<SI>" }, 		     { 16, "<DLE>" }, 		     { 17, "<DC1>" }, 		     { 18, "<DC2>" }, 		     { 19, "<DC3>" }, 		     { 20, "<DC4>" }, 		     { 21, "<NAK>" }, 		     { 22, "<SYN>" }, 		     { 23, "<ETB>" }, 		     { 24, "<CAN>" }, 		     { 25, "<EM>" }, 		     { 26, "<SUB>" }, 		     { 27, "<ESC>" }, 		     { 28, "<FS>" }, 		     { 29, "<GS>" }, 		     { 30, "<RS>" }, 		     { 31, "<US>" }, #ifdef CHARSET_LATIN1		     { 0x5b, "\304" }, /* upper case A dieresis */		     { 0x5c, "\326" }, /* upper case O dieresis */		     { 0x5d, "\334" }, /* upper case U dieresis */ 		     { 0x7b, "\344" }, /* lower case a dieresis */		     { 0x7c, "\366" }, /* lower case o dieresis */ 		     { 0x7d, "\374" }, /* lower case u dieresis */ 		     { 0x7e, "\337" }}; /* sharp s */#else /* CHARSET_LATIN1 */		     { 0x5b, "AE" }, /* upper case A dieresis */		     { 0x5c, "OE" }, /* upper case O dieresis */		     { 0x5d, "UE" }, /* upper case U dieresis */ 		     { 0x7b, "ae" }, /* lower case a dieresis */		     { 0x7c, "oe" }, /* lower case o dieresis */ 		     { 0x7d, "ue" }, /* lower case u dieresis */ 		     { 0x7e, "ss" }}; /* sharp s */#endif /* CHARSET_LATIN1 */	int min = 0, max = (sizeof(trtab) / sizeof(trtab[0])) - 1;		/*	 * binary search, list must be ordered!	 */	for (;;) {		int mid = (min+max) >> 1;		const struct trtab *tb = trtab + mid;		int cmp = ((int) tb->code) - ((int) chr);		if (!cmp)			return tb->str;		if (cmp < 0) {			min = mid+1;			if (min > max)				return NULL;		}		if (cmp > 0) {			max = mid-1;			if (max < min)				return NULL;		}	}}				/* ---------------------------------------------------------------------- */static void print_msg_alpha(struct l2_pocsag_rx *rx) {	unsigned long data = 0;	int datalen = 0;	unsigned char *bp = rx->buffer;	int len = rx->numnibbles;	char buf[256], *cp = buf;	int buffree = sizeof(buf)-1;	unsigned char curchr;	char *tstr;		while (len > 0) {		while (datalen < 7 && len > 0) {			if (len == 1) {				data = (data << 4) | ((*bp >> 4) & 0xf);				datalen += 4;				len = 0;			} else {				data = (data << 8) | *bp++;				datalen += 8;				len -= 2;			}		}		if (datalen < 7)			continue;		datalen -= 7;		curchr = ((data >> datalen) & 0x7f) << 1;		curchr = ((curchr & 0xf0) >> 4) | ((curchr & 0x0f) << 4);		curchr = ((curchr & 0xcc) >> 2) | ((curchr & 0x33) << 2);		curchr = ((curchr & 0xaa) >> 1) | ((curchr & 0x55) << 1);		tstr = translate_alpha(curchr);		if (tstr) {			int tlen = strlen(tstr);			if (buffree >= tlen) {				memcpy(cp, tstr, tlen);				cp += tlen;				buffree -= tlen;			}		} else if (buffree > 0) {			*cp++ = curchr;			buffree--;		}	}	*cp = '\0';	verbprintf(0, "%s\n", buf);}/* ---------------------------------------------------------------------- */static void print_msg_skyper(struct l2_pocsag_rx *rx) {	unsigned long data = 0;	int datalen = 0;	unsigned char *bp = rx->buffer;	int len = rx->numnibbles;	char buf[256], *cp = buf;	int buffree = sizeof(buf)-1;	unsigned char curchr;	char *tstr;		while (len > 0) {		while (datalen < 7 && len > 0) {			if (len == 1) {				data = (data << 4) | ((*bp >> 4) & 0xf);				datalen += 4;				len = 0;			} else {				data = (data << 8) | *bp++;				datalen += 8;				len -= 2;			}		}		if (datalen < 7)			continue;		datalen -= 7;		curchr = ((data >> datalen) & 0x7f) << 1;		curchr = ((curchr & 0xf0) >> 4) | ((curchr & 0x0f) << 4);		curchr = ((curchr & 0xcc) >> 2) | ((curchr & 0x33) << 2);		curchr = ((curchr & 0xaa) >> 1) | ((curchr & 0x55) << 1);		tstr = translate_alpha(curchr-1);		if (tstr) {			int tlen = strlen(tstr);			if (buffree >= tlen) {				memcpy(cp, tstr, tlen);				cp += tlen;				buffree -= tlen;			}		} else if (buffree > 0) {			*cp++ = curchr-1;			buffree--;		}	}	*cp = '\0';	verbprintf(0, "%s\n", buf);}/* ---------------------------------------------------------------------- */static void pocsag_printmessage(struct demod_state *s, struct l2_pocsag_rx *rx, 				const char *add_name) {	verbprintf(0, "%s%s: Address: %7lu  Function: %1u\n",		   s->dem_par->name, add_name, rx->adr, rx->func);	if (!rx->numnibbles)		return;	if (service_mask & (0x01 << rx->func)) {		verbprintf(0, "%s%s: Numeric: ", s->dem_par->name, add_name);		print_msg_numeric(rx);	}	if (service_mask & (0x10 << rx->func)) {		if (rx->func == 3 && rx->adr >= 4000 &&		    rx->adr <= 5000) {			verbprintf(0, "%s%s: Alpha (SKYPER): ", s->dem_par->name, add_name);			print_msg_skyper(rx);		} else {			verbprintf(0, "%s%s: Alpha: ", s->dem_par->name, add_name);			print_msg_alpha(rx);		}	}}/* ---------------------------------------------------------------------- */void pocsag_init(struct demod_state *s){	memset(&s->l2.pocsag, 0, sizeof(s->l2.pocsag));}/* ---------------------------------------------------------------------- */static void do_one_bit(struct demod_state *s, struct l2_pocsag_rx *rx, 		       unsigned long rx_data, const char *add_name){	unsigned char rxword;	if (!rx->rx_sync) {		if (rx_data == POCSAG_SYNC || rx_data == POCSAG_SYNCINFO) {			rx->rx_sync = 2;			rx->rx_bit = rx->rx_word = 0;			rx->func = -1;			return;		}		return;	}   		if ((++(rx->rx_bit)) < 32) 		return;	/*	 * one complete word received	 */	rx->rx_bit = 0;	/*	 * check codeword	 */	if (pocsag_syndrome(rx_data)) {		/*		 * codeword not valid		 */		rx->rx_sync--;		verbprintf(7, "%s: Bad codeword: %08lx%s\n", 			   s->dem_par->name, rx_data, 			   rx->rx_sync ? "" : "sync lost");		if (!(rx->func & (~3))) {			verbprintf(0, "%s%s: Warning: message garbled\n",				   s->dem_par->name, add_name);			pocsag_printmessage(s, rx, add_name);		}		rx->func = -1; /* invalidate message */		return;	}	/* do something with the data */	verbprintf(8, "%s%s: Codeword: %08lx\n", s->dem_par->name, add_name, rx_data);	rxword = rx->rx_word++;	if (rxword >= 16) {		/*		 * received word shoud be a		 * frame synch		 */		rx->rx_word = 0;		if ((rx_data == POCSAG_SYNC) ||		    (rx_data == POCSAG_SYNCINFO))			rx->rx_sync = 10;		else			rx->rx_sync -= 2;		return;		}	if (rx_data == POCSAG_IDLE) {		/*		 * it seems that we can output the message right here		 */		if (!(rx->func & (~3)))			pocsag_printmessage(s, rx, add_name);		rx->func = -1; /* invalidate message */		return;	}	if (rx_data & 0x80000000) {		/*		 * this is a data word		 */		unsigned long data;		unsigned char *bp;				if (rx->func & (~3)) { 			/*			 * no message being received 			 */			verbprintf(7, "%s%s: Lonesome data codeword: %08lx\n",				   s->dem_par->name, add_name, rx_data);			return;		}		if (rx->numnibbles > sizeof(rx->buffer)*2 - 5) {			verbprintf(0, "%s%s: Warning: Message too long\n",				   s->dem_par->name, add_name);			pocsag_printmessage(s, rx, add_name);			rx->func = -1;			return;		}		bp = rx->buffer + (rx->numnibbles >> 1);		data = rx_data >> 11; 		if (rx->numnibbles & 1) {			bp[0] = (bp[0] & 0xf0) | ((data >> 16) & 0xf);			bp[1] = data >> 8;			bp[2] = data;		} else {			bp[0] = data >> 12;			bp[1] = data >> 4;			bp[2] = data << 4;		}		rx->numnibbles += 5;		return;	}	/*	 * process address codeword	 */	if (rx_data >= POCSAG_SYNC_WORDS) {		unsigned char func = (rx_data >> 11) & 3;		unsigned long adr = ((rx_data >> 10) & 0x1ffff8) | 			((rxword >> 1) & 7);		verbprintf(0, "%s%s: Nonstandard address codeword: %08lx "			   "func %1u adr %08lx\n", s->dem_par->name, add_name, rx_data, 			   func, adr);		return;	}	if (!(rx->func & (~3))) 		pocsag_printmessage(s, rx, add_name);	rx->func = (rx_data >> 11) & 3;	rx->adr = ((rx_data >> 10) & 0x1ffff8) | ((rxword >> 1) & 7);	rx->numnibbles = 0;}/* ---------------------------------------------------------------------- */void pocsag_rxbit(struct demod_state *s, int bit){	s->l2.pocsag.rx_data <<= 1;	s->l2.pocsag.rx_data |= !bit;	verbprintf(9, " %c ", '1'-(s->l2.pocsag.rx_data & 1));	do_one_bit(s, s->l2.pocsag.rx, ~(s->l2.pocsag.rx_data), "+");	do_one_bit(s, s->l2.pocsag.rx+1, s->l2.pocsag.rx_data, "-");}/* ---------------------------------------------------------------------- */