/* $Id: rawhdlc.c,v 1.1 2004/03/11 03:59:31 bcrl Exp $ * * rawhdlc.c support routines for cards that don't support HDLC * * Author Karsten Keil (keil@isdn4linux.de) * Brent Baccala * * This file is (c) under GNU PUBLIC LICENSE * * Some passive ISDN cards, such as the Traverse NETJet and the AMD 7930, * don't perform HDLC encapsulation over the B channel. Drivers for * such cards use support routines in this file to perform B channel HDLC. * * Bit-synchronous HDLC encapsulation is a means of encapsulating packets * over a continuously transmitting serial communications link. * It looks like this: * * 11111111101111110...........0111111011111111111 * iiiiiiiiiffffffffdddddddddddffffffffiiiiiiiiiii * * i = idle f = flag d = data * * When idle, the channel sends a continuous string of ones (mark * idle; illustrated), or a continuous string of flag characters (flag * idle). The beginning of a data frame is marked by a flag character * (01111110), then comes the actual data, followed by another flag * character, after which another frame may be sent immediately (a * single flag may serve as both the end of one frame and the start of * the next), or the link may return to idle. Obviously, the flag * character can not appear anywhere in the data (or a false * end-of-frame would occur), so the transmitter performs * "bit-stuffing" - inserting a zero bit after every five one bits, * irregardless of the original bit after the five ones. Byte * ordering is irrelevent at this point - the data is treated as a * string of bits, not bytes. Since no more than 5 ones may now occur * in a row, the flag sequence, with its 6 ones, is unique. * * Upon reception, a zero bit that occur after 5 one bits is simply * discarded. A series of 6 one bits is end-of-frame, and a series of * 7 one bits is an abort. Once bit-stuffing has been corrected for, * an integer number of bytes should now be present. The last two * of these bytes form the Frame Check Sequence, a CRC that is verified * and then discarded. Note that bit-stuffing is performed on the FCS * just as if it were regular data. * * * * int make_raw_hdlc_data(u_char *src, u_int slen, * u_char *dst, u_int dsize) * * Used for transmission. Copies slen bytes from src to dst, performing * HDLC encapsulation (flag bytes, bit-stuffing, CRC) in the process. * dsize is size of destination buffer, and should be at least * ((6*slen)/5)+5 bytes to ensure adequate space will be available. * Function returns length (in bytes) of valid destination buffer, or * 0 upon destination overflow. * * void init_hdlc_state(struct hdlc_state *stateptr, int mode) * * Initializes hdlc_state structure before first call to read_raw_hdlc_data * * mode = 0: Sane mode * mode = 1/2: * Insane mode; NETJet use a shared unsigned int memory block ( * with busmaster DMA), the bit pattern of every word is * <8 B1> <8 B2> <8 Mon> <2 D> <4 C/I> * according to Siemens IOM-2 interface, so we have to handle * the src buffer as unsigned int and have to shift/mask the * B-channel bytes. * mode 1 -> B1 mode 2 -> B2 data is used * * int read_raw_hdlc_data(struct hdlc_state *saved_state, * u_char *src, u_int slen, * u_char *dst, u_int dsize) * * Used for reception. Scans source buffer bit-by-bit looking for * valid HDLC frames, which are copied to destination buffer. HDLC * state information is stored in a structure, which allows this * function to process frames spread across several blocks of raw * HDLC data. Part of the state information is bit offsets into * the source and destination buffers. * * A return value >0 indicates the length of a valid frame, now * stored in the destination buffer. In this case, the source * buffer might not be completely processed, so this function should * be called again with the same source buffer, possibly with a * different destination buffer. * * A return value of zero indicates that the source buffer was * completely processed without finding a valid end-of-packet; * however, we might be in the middle of packet reception, so * the function should be called again with the next block of * raw HDLC data and the same destination buffer. It is NOT * permitted to change the destination buffer in this case, * since data may already have begun to be stored there. * * A return value of -1 indicates some kind of error - destination * buffer overflow, CRC check failed, frame not a multiple of 8 * bits. Destination buffer probably contains invalid data, which * should be discarded. Call function again with same source buffer * and a new (or same) destination buffer. * * Suggested calling sequence: * * init_hdlc_state(...); * for (EACH_RAW_DATA_BLOCK) { * while (len = read_raw_hdlc_data(...)) { * if (len == -1) DISCARD_FRAME; * else PROCESS_FRAME; * } * } * * * Test the code in this file as follows: * gcc -DDEBUGME -o rawhdlctest rawhdlc.c * ./rawhdlctest < rawdata * * The file "rawdata" can be easily generated from a HISAX B-channel * hex dump (CF CF CF 02 ...) using the following perl script: * * while(<>) { * @hexlist = split ' '; * while ($hexstr = shift(@hexlist)) { * printf "%c", hex($hexstr); * } * } * */ #ifdef DEBUGME #include #endif #include #include #include "rawhdlc.h" /* There's actually an identical copy of this table in the PPP code * (ppp_crc16_table), but I don't want this code dependent on PPP */ // static __u16 fcstab[256] = { 0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5, 0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974, 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb, 0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a, 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, 0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70, 0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff, 0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134, 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c, 0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb, 0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9, 0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78 }; #define HDLC_ZERO_SEARCH 0 #define HDLC_FLAG_SEARCH 1 #define HDLC_FLAG_FOUND 2 #define HDLC_FRAME_FOUND 3 #define HDLC_NULL 4 #define HDLC_PART 5 #define HDLC_FULL 6 #define HDLC_FLAG_VALUE 0x7e #define MAKE_RAW_BYTE for (j=0; j<8; j++) { \ bitcnt++;\ out_val >>= 1;\ if (val & 1) {\ s_one++;\ out_val |= 0x80;\ } else {\ s_one = 0;\ out_val &= 0x7f;\ }\ if (bitcnt==8) {\ if (d_cnt == dsize) return 0;\ dst[d_cnt++] = out_val;\ bitcnt = 0;\ }\ if (s_one == 5) {\ out_val >>= 1;\ out_val &= 0x7f;\ bitcnt++;\ s_one = 0;\ }\ if (bitcnt==8) {\ if (d_cnt == dsize) return 0;\ dst[d_cnt++] = out_val;\ bitcnt = 0;\ }\ val >>= 1;\ } /* Optimization suggestion: If needed, this function could be * dramatically sped up using a state machine. Each state would * correspond to having seen N one bits, and being offset M bits into * the current output byte. N ranges from 0 to 4, M from 0 to 7, so * we need 5*8 = 35 states. Each state would have a table with 256 * entries, one for each input character. Each entry would contain * three output characters, an output state, an a byte increment * that's either 1 or 2. All this could fit in four bytes; so we need * 4 bytes * 256 characters = 1 KB for each state (35 KB total). Zero * the output buffer before you start. For each character in your * input, you look it up in the current state's table and get three * bytes to be or'ed into the output at the current byte offset, and * an byte increment to move your pointer forward. A simple Perl * script could generate the tables. Given HDLC semantics, probably * would be better to set output to all 1s, then use ands instead of ors. * A smaller state machine could operate on nibbles instead of bytes. * A state machine for 32-bit architectures could use word offsets * instead of byte offsets, requiring 5*32 = 160 states; probably * best to work on nibbles in such a case. */ int make_raw_hdlc_data(u_char *src, u_int slen, u_char *dst, u_int dsize) { register u_int i,d_cnt=0; register u_char j; register u_char val; register u_char s_one = 0; register u_char out_val = 0; register u_char bitcnt = 0; u_int fcs; dst[d_cnt++] = HDLC_FLAG_VALUE; fcs = PPP_INITFCS; for (i=0; i>8) & 0xff; MAKE_RAW_BYTE; val = HDLC_FLAG_VALUE; for (j=0; j<8; j++) { bitcnt++; out_val >>= 1; if (val & 1) out_val |= 0x80; else out_val &= 0x7f; if (bitcnt==8) { if (d_cnt == dsize) return 0; dst[d_cnt++] = out_val; bitcnt = 0; } val >>= 1; } if (bitcnt) { while (8>bitcnt++) { out_val >>= 1; out_val |= 0x80; } if (d_cnt == dsize) return 0; dst[d_cnt++] = out_val; } return d_cnt; } void init_hdlc_state(struct hdlc_state *stateptr, int mode) { stateptr->state = HDLC_ZERO_SEARCH; stateptr->r_one = 0; stateptr->r_val = 0; stateptr->o_bitcnt = 0; stateptr->i_bitcnt = 0; stateptr->insane_mode = mode; } /* Optimization suggestion: A similar state machine could surely * be developed for this function as well. */ int read_raw_hdlc_data(struct hdlc_state *saved_state, u_char *src, u_int slen, u_char *dst, u_int dsize) { int retval=0; register u_char val; register u_char state = saved_state->state; register u_char r_one = saved_state->r_one; register u_char r_val = saved_state->r_val; register u_int o_bitcnt = saved_state->o_bitcnt; register u_int i_bitcnt = saved_state->i_bitcnt; register u_int fcs = saved_state->fcs; register u_int *isrc = (u_int *) src; /* Use i_bitcnt (bit offset into source buffer) to reload "val" * in case we're starting up again partway through a source buffer */ if ((i_bitcnt >> 3) < slen) { if (saved_state->insane_mode==1) { val = isrc[(i_bitcnt >> 3)] & 0xff; } else if (saved_state->insane_mode==2) { val = (isrc[i_bitcnt >> 3] >>8) & 0xff; } else { val = src[i_bitcnt >> 3]; } val >>= i_bitcnt & 7; } /* One bit per loop. Keep going until we've got something to * report (retval != 0), or we exhaust the source buffer */ while ((retval == 0) && ((i_bitcnt >> 3) < slen)) { if ((i_bitcnt & 7) == 0) { if (saved_state->insane_mode==1) { val = isrc[(i_bitcnt >> 3)] & 0xff; } else if (saved_state->insane_mode==2) { val = (isrc[i_bitcnt >> 3] >>8) & 0xff; } else { val = src[i_bitcnt >> 3]; } #ifdef DEBUGME printf("Input byte %d: 0x%2x\n", i_bitcnt>>3, val); #endif if (val == 0xff) { state = HDLC_ZERO_SEARCH; o_bitcnt = 0; r_one = 0; i_bitcnt += 8; continue; } } #ifdef DEBUGME /* printf("Data bit=%d (%d/%d)\n", val&1, i_bitcnt>>3, i_bitcnt&7);*/ #endif if (state == HDLC_ZERO_SEARCH) { if (val & 1) { r_one++; } else { r_one=0; state= HDLC_FLAG_SEARCH; } } else if (state == HDLC_FLAG_SEARCH) { if (val & 1) { r_one++; if (r_one>6) { state=HDLC_ZERO_SEARCH; } } else { if (r_one==6) { o_bitcnt=0; r_val=0; state=HDLC_FLAG_FOUND; } r_one=0; } } else if (state == HDLC_FLAG_FOUND) { if (val & 1) { r_one++; if (r_one>6) { state=HDLC_ZERO_SEARCH; } else { r_val >>= 1; r_val |= 0x80; o_bitcnt++; } } else { if (r_one==6) { o_bitcnt=0; r_val=0; r_one=0; i_bitcnt++; val >>= 1; continue; } else if (r_one!=5) { r_val >>= 1; r_val &= 0x7f; o_bitcnt++; } r_one=0; } if ((state != HDLC_ZERO_SEARCH) && !(o_bitcnt & 7)) { #ifdef DEBUGME printf("HDLC_FRAME_FOUND at i_bitcnt:%d\n",i_bitcnt); #endif state=HDLC_FRAME_FOUND; fcs = PPP_INITFCS; dst[0] = r_val; fcs = PPP_FCS (fcs, r_val); } } else if (state == HDLC_FRAME_FOUND) { if (val & 1) { r_one++; if (r_one>6) { state=HDLC_ZERO_SEARCH; o_bitcnt=0; } else { r_val >>= 1; r_val |= 0x80; o_bitcnt++; } } else { if (r_one==6) { r_val=0; r_one=0; o_bitcnt++; if (o_bitcnt & 7) { /* Alignment error */ #ifdef DEBUGME printf("Alignment error\n"); #endif state=HDLC_FLAG_SEARCH; retval = -1; } else if (fcs==PPP_GOODFCS) { /* Valid frame */ state=HDLC_FLAG_FOUND; retval = (o_bitcnt>>3)-3; } else { /* CRC error */ #ifdef DEBUGME printf("CRC error; fcs was 0x%x, should have been 0x%x\n", fcs, PPP_GOODFCS); #endif state=HDLC_FLAG_FOUND; retval = -1; } } else if (r_one==5) { r_one=0; i_bitcnt++; val >>= 1; continue; } else { r_val >>= 1; r_val &= 0x7f; o_bitcnt++; } r_one=0; } if ((state == HDLC_FRAME_FOUND) && !(o_bitcnt & 7)) { if ((o_bitcnt>>3)>=dsize) { /* Buffer overflow error */ #ifdef DEBUGME printf("Buffer overflow error\n"); #endif r_val=0; state=HDLC_FLAG_SEARCH; retval = -1; } else { dst[(o_bitcnt>>3)-1] = r_val; fcs = PPP_FCS (fcs, r_val); #ifdef DEBUGME printf("Output byte %d: 0x%02x; FCS 0x%04x\n", (o_bitcnt>>3)-1, r_val, fcs); #endif } } } i_bitcnt ++; val >>= 1; } /* We exhausted the source buffer before anything else happened * (retval==0). Reset i_bitcnt in expectation of a new source * buffer. Other, we either had an error or a valid frame, so * reset o_bitcnt in expectation of a new destination buffer. */ if (retval == 0) { i_bitcnt = 0; } else { o_bitcnt = 0; } saved_state->state = state; saved_state->r_one = r_one; saved_state->r_val = r_val; saved_state->fcs = fcs; saved_state->o_bitcnt = o_bitcnt; saved_state->i_bitcnt = i_bitcnt; return (retval); } #ifdef DEBUGME char buffer[1024]; char obuffer[1024]; main() { int buflen=0; int len; struct hdlc_state hdlc_state; while((buffer[buflen] = getc(stdin)) != EOF && buflen<1024) buflen++; printf("buflen = %d\n", buflen); init_hdlc_state(&hdlc_state, 0); while (len = read_raw_hdlc_data(&hdlc_state,buffer,buflen,obuffer,1024)) { if (len == -1) printf("Error @ byte %d/bit %d\n", hdlc_state.i_bitcnt>>3, hdlc_state.i_bitcnt & 7); else { printf("Frame received: len %d\n", len); } } printf("Done\n"); } #endif