/*
isdnhdlc_decode - decodes HDLC frames from a transparent bit stream.
The source buffer is scanned for valid HDLC frames looking for
flags (01111110) to indicate the start of a frame. If the start of
the frame is found, the bit stuffing is removed (0 after 5 1's).
When a new flag is found, the complete frame has been received
and the CRC is checked.
If a valid frame is found, the function returns the frame length
excluding the CRC with the bit HDLC_END_OF_FRAME set.
If the beginning of a valid frame is found, the function returns
the length.
If a framing error is found (too many 1s and not a flag) the function
returns the length with the bit HDLC_FRAMING_ERROR set.
If a CRC error is found the function returns the length with the
bit HDLC_CRC_ERROR set.
If the frame length exceeds the destination buffer size, the function
returns the length with the bit HDLC_LENGTH_ERROR set.
src - source buffer
slen - source buffer length
count - number of bytes removed (decoded) from the source buffer
dst _ destination buffer
dsize - destination buffer size
returns - number of decoded bytes in the destination buffer and status
flag.
*/
int isdnhdlc_decode (struct isdnhdlc_vars *hdlc, const unsigned char *src,
int slen, int *count, unsigned char *dst, int dsize)
{
int status=0;
static const unsigned char fast_flag[]={
0x00,0x00,0x00,0x20,0x30,0x38,0x3c,0x3e,0x3f
};
static const unsigned char fast_flag_value[]={
0x00,0x7e,0xfc,0xf9,0xf3,0xe7,0xcf,0x9f,0x3f
};
static const unsigned char fast_abort[]={
0x00,0x00,0x80,0xc0,0xe0,0xf0,0xf8,0xfc,0xfe,0xff
};
*count = slen;
while(slen > 0){
if(hdlc->bit_shift==0){
hdlc->cbin = *src++;
slen--;
hdlc->bit_shift = 8;
if(hdlc->do_adapt56){
hdlc->bit_shift --;
}
}
switch(hdlc->state){
case STOPPED:
return 0;
case HDLC_FAST_IDLE:
if(hdlc->cbin == 0xff){
hdlc->bit_shift = 0;
break;
}
hdlc->state = HDLC_GET_FLAG_B0;
hdlc->hdlc_bits1 = 0;
hdlc->bit_shift = 8;
break;
case HDLC_GET_FLAG_B0:
if(!(hdlc->cbin & 0x80)) {
hdlc->state = HDLC_GETFLAG_B1A6;
hdlc->hdlc_bits1 = 0;
} else {
if(!hdlc->do_adapt56){
if(++hdlc->hdlc_bits1 >=8 ) if(hdlc->bit_shift==1)
hdlc->state = HDLC_FAST_IDLE;
}
}
hdlc->cbin<<=1;
hdlc->bit_shift --;
break;
case HDLC_GETFLAG_B1A6:
if(hdlc->cbin & 0x80){
hdlc->hdlc_bits1++;
if(hdlc->hdlc_bits1==6){
hdlc->state = HDLC_GETFLAG_B7;
}
} else {
hdlc->hdlc_bits1 = 0;
}
hdlc->cbin<<=1;
hdlc->bit_shift --;
break;
case HDLC_GETFLAG_B7:
if(hdlc->cbin & 0x80) {
hdlc->state = HDLC_GET_FLAG_B0;
} else {
hdlc->state = HDLC_GET_DATA;
hdlc->crc = 0xffff;
hdlc->shift_reg = 0;
hdlc->hdlc_bits1 = 0;
hdlc->data_bits = 0;
hdlc->data_received = 0;
}
hdlc->cbin<<=1;
hdlc->bit_shift --;
break;
case HDLC_GET_DATA:
if(hdlc->cbin & 0x80){
hdlc->hdlc_bits1++;
switch(hdlc->hdlc_bits1){
case 6:
break;
case 7:
if(hdlc->data_received) {
// bad frame
status = -HDLC_FRAMING_ERROR;
}
if(!hdlc->do_adapt56){
if(hdlc->cbin==fast_abort[hdlc->bit_shift+1]){
hdlc->state = HDLC_FAST_IDLE;
hdlc->bit_shift=1;
break;
}
} else {
hdlc->state = HDLC_GET_FLAG_B0;
}
break;
default:
hdlc->shift_reg>>=1;
hdlc->shift_reg |= 0x80;
hdlc->data_bits++;
break;
}
} else {
switch(hdlc->hdlc_bits1){
case 5:
break;
case 6:
if(hdlc->data_received){
if (hdlc->dstpos < 2) {
status = -HDLC_FRAMING_ERROR;
} else if (hdlc->crc != 0xf0b8){
// crc error
status = -HDLC_CRC_ERROR;
} else {
// remove CRC
hdlc->dstpos -= 2;
// good frame
status = hdlc->dstpos;
}
}
hdlc->crc = 0xffff;
hdlc->shift_reg = 0;
hdlc->data_bits = 0;
if(!hdlc->do_adapt56){
if(hdlc->cbin==fast_flag[hdlc->bit_shift]){
hdlc->ffvalue = fast_flag_value[hdlc->bit_shift];
hdlc->state = HDLC_FAST_FLAG;
hdlc->ffbit_shift = hdlc->bit_shift;
hdlc->bit_shift = 1;
} else {
hdlc->state = HDLC_GET_DATA;
hdlc->data_received = 0;
}
} else {
hdlc->state = HDLC_GET_DATA;
hdlc->data_received = 0;
}
break;
default:
hdlc->shift_reg>>=1;
hdlc->data_bits++;
break;
}
hdlc->hdlc_bits1 = 0;
}
if (status) {
hdlc->dstpos = 0;
*count -= slen;
hdlc->cbin <<= 1;
hdlc->bit_shift--;
return status;
}
if(hdlc->data_bits==8){
hdlc->data_bits = 0;
hdlc->data_received = 1;
hdlc->crc = crc_ccitt_byte(hdlc->crc, hdlc->shift_reg);
// good byte received
if (dsize--) {
dst[hdlc->dstpos++] = hdlc->shift_reg;
} else {
// frame too long
status = -HDLC_LENGTH_ERROR;
hdlc->dstpos = 0;
}
}
hdlc->cbin <<= 1;
hdlc->bit_shift--;
break;
case HDLC_FAST_FLAG:
if(hdlc->cbin==hdlc->ffvalue){
hdlc->bit_shift = 0;
break;
} else {
if(hdlc->cbin == 0xff){
hdlc->state = HDLC_FAST_IDLE;
hdlc->bit_shift=0;
} else if(hdlc->ffbit_shift==8){
hdlc->state = HDLC_GETFLAG_B7;
break;
} else {
hdlc->shift_reg = fast_abort[hdlc->ffbit_shift-1];
hdlc->hdlc_bits1 = hdlc->ffbit_shift-2;
if(hdlc->hdlc_bits1<0)hdlc->hdlc_bits1 = 0;
hdlc->data_bits = hdlc->ffbit_shift-1;
hdlc->state = HDLC_GET_DATA;
hdlc->data_received = 0;
}
}
break;
default:
break;
}
/*
isdnhdlc_decode - decodes HDLC frames from a transparent bit stream.
The source buffer is scanned for valid HDLC frames looking for
flags (01111110) to indicate the start of a frame. If the start of
the frame is found, the bit stuffing is removed (0 after 5 1's).
When a new flag is found, the complete frame has been received
and the CRC is checked.
If a valid frame is found, the function returns the frame length
excluding the CRC with the bit HDLC_END_OF_FRAME set.
If the beginning of a valid frame is found, the function returns
the length.
If a framing error is found (too many 1s and not a flag) the function
returns the length with the bit HDLC_FRAMING_ERROR set.
If a CRC error is found the function returns the length with the
bit HDLC_CRC_ERROR set.
If the frame length exceeds the destination buffer size, the function
returns the length with the bit HDLC_LENGTH_ERROR set.
src - source buffer
slen - source buffer length
count - number of bytes removed (decoded) from the source buffer
dst _ destination buffer
dsize - destination buffer size
returns - number of decoded bytes in the destination buffer and status
flag.
*/
int isdnhdlc_decode(struct isdnhdlc_vars *hdlc, const u8 *src, int slen,
int *count, u8 *dst, int dsize)
{
int status = 0;
static const unsigned char fast_flag[] = {
0x00, 0x00, 0x00, 0x20, 0x30, 0x38, 0x3c, 0x3e, 0x3f
};
static const unsigned char fast_flag_value[] = {
0x00, 0x7e, 0xfc, 0xf9, 0xf3, 0xe7, 0xcf, 0x9f, 0x3f
};
static const unsigned char fast_abort[] = {
0x00, 0x00, 0x80, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc, 0xfe, 0xff
};
#define handle_fast_flag(h) \
do { \
if (h->cbin == fast_flag[h->bit_shift]) { \
h->ffvalue = fast_flag_value[h->bit_shift]; \
h->state = HDLC_FAST_FLAG; \
h->ffbit_shift = h->bit_shift; \
h->bit_shift = 1; \
} else { \
h->state = HDLC_GET_DATA; \
h->data_received = 0; \
} \
} while (0)
#define handle_abort(h) \
do { \
h->shift_reg = fast_abort[h->ffbit_shift - 1]; \
h->hdlc_bits1 = h->ffbit_shift - 2; \
if (h->hdlc_bits1 < 0) \
h->hdlc_bits1 = 0; \
h->data_bits = h->ffbit_shift - 1; \
h->state = HDLC_GET_DATA; \
h->data_received = 0; \
} while (0)
*count = slen;
while (slen > 0) {
if (hdlc->bit_shift == 0) {
/* the code is for bitreverse streams */
if (hdlc->do_bitreverse == 0)
hdlc->cbin = bitrev8(*src++);
else
hdlc->cbin = *src++;
slen--;
hdlc->bit_shift = 8;
if (hdlc->do_adapt56)
hdlc->bit_shift--;
}
switch (hdlc->state) {
case STOPPED:
return 0;
case HDLC_FAST_IDLE:
if (hdlc->cbin == 0xff) {
hdlc->bit_shift = 0;
break;
}
hdlc->state = HDLC_GET_FLAG_B0;
hdlc->hdlc_bits1 = 0;
hdlc->bit_shift = 8;
break;
case HDLC_GET_FLAG_B0:
if (!(hdlc->cbin & 0x80)) {
hdlc->state = HDLC_GETFLAG_B1A6;
hdlc->hdlc_bits1 = 0;
} else {
if ((!hdlc->do_adapt56) &&
(++hdlc->hdlc_bits1 >= 8) &&
(hdlc->bit_shift == 1))
hdlc->state = HDLC_FAST_IDLE;
}
hdlc->cbin <<= 1;
hdlc->bit_shift--;
break;
case HDLC_GETFLAG_B1A6:
if (hdlc->cbin & 0x80) {
hdlc->hdlc_bits1++;
if (hdlc->hdlc_bits1 == 6)
hdlc->state = HDLC_GETFLAG_B7;
} else
hdlc->hdlc_bits1 = 0;
hdlc->cbin <<= 1;
hdlc->bit_shift--;
break;
case HDLC_GETFLAG_B7:
if (hdlc->cbin & 0x80) {
hdlc->state = HDLC_GET_FLAG_B0;
} else {
hdlc->state = HDLC_GET_DATA;
hdlc->crc = 0xffff;
hdlc->shift_reg = 0;
hdlc->hdlc_bits1 = 0;
hdlc->data_bits = 0;
hdlc->data_received = 0;
}
hdlc->cbin <<= 1;
hdlc->bit_shift--;
break;
case HDLC_GET_DATA:
if (hdlc->cbin & 0x80) {
hdlc->hdlc_bits1++;
switch (hdlc->hdlc_bits1) {
case 6:
break;
case 7:
if (hdlc->data_received)
/* bad frame */
status = -HDLC_FRAMING_ERROR;
if (!hdlc->do_adapt56) {
if (hdlc->cbin == fast_abort
[hdlc->bit_shift + 1]) {
hdlc->state =
HDLC_FAST_IDLE;
hdlc->bit_shift = 1;
break;
}
} else
hdlc->state = HDLC_GET_FLAG_B0;
break;
default:
hdlc->shift_reg >>= 1;
hdlc->shift_reg |= 0x80;
hdlc->data_bits++;
break;
}
} else {
switch (hdlc->hdlc_bits1) {
case 5:
break;
case 6:
if (hdlc->data_received)
status = check_frame(hdlc);
hdlc->crc = 0xffff;
hdlc->shift_reg = 0;
hdlc->data_bits = 0;
if (!hdlc->do_adapt56)
handle_fast_flag(hdlc);
else {
hdlc->state = HDLC_GET_DATA;
hdlc->data_received = 0;
}
break;
default:
hdlc->shift_reg >>= 1;
hdlc->data_bits++;
break;
}
hdlc->hdlc_bits1 = 0;
}
if (status) {
hdlc->dstpos = 0;
*count -= slen;
hdlc->cbin <<= 1;
hdlc->bit_shift--;
return status;
}
if (hdlc->data_bits == 8) {
hdlc->data_bits = 0;
hdlc->data_received = 1;
hdlc->crc = crc_ccitt_byte(hdlc->crc,
hdlc->shift_reg);
/* good byte received */
if (hdlc->dstpos < dsize)
dst[hdlc->dstpos++] = hdlc->shift_reg;
else {
/* frame too long */
status = -HDLC_LENGTH_ERROR;
hdlc->dstpos = 0;
}
}
hdlc->cbin <<= 1;
hdlc->bit_shift--;
break;
case HDLC_FAST_FLAG:
if (hdlc->cbin == hdlc->ffvalue) {
hdlc->bit_shift = 0;
break;
} else {
if (hdlc->cbin == 0xff) {
hdlc->state = HDLC_FAST_IDLE;
hdlc->bit_shift = 0;
} else if (hdlc->ffbit_shift == 8) {
hdlc->state = HDLC_GETFLAG_B7;
break;
} else
handle_abort(hdlc);
}
break;
default:
break;
}
/**
* crc_ccitt - recompute the CRC for the data buffer
* @crc: previous CRC value
* @buffer: data pointer
* @len: number of bytes in the buffer
*/
quint16 crc_ccitt(quint16 crc, uchar const *buffer, size_t len)
{
while (len--)
crc = crc_ccitt_byte(crc, *buffer++);
return crc;
}
/**
* crc_ccitt - recompute the CRC for the data buffer
* @crc - previous CRC value
* @buffer - data pointer
* @len - number of bytes in the buffer
*/
u16 crc_ccitt(u16 crc, u8 const *buffer, size_t len)
{
while (len--)
crc = crc_ccitt_byte(crc, *buffer++);
return crc;
}
