leansdr::hdlc_dec Struct Reference

#include <hdlc.h>

Public Member Functions
	hdlc_dec (int _minframesize, int _maxframesize, bool _invert)
void	reset ()
void	begin_frame ()
u8 *	decode (u8 **ppin, int count, int *pdatasize, int *hdlc_errors, int *fcs_errors)

Public Attributes
bool	debug

Private Member Functions
void	crc16_byte (u8 data)

Private Attributes
int	minframesize
int	maxframesize
u8	invertmask
u8 *	framebuf
u8	shiftreg
bool	inframe
u8	byte_out
int	nbits_out
int	framesize
u16	crc16

Static Private Attributes
static const u16	crc16_init = 0xffff
static const u16	crc16_poly = 0x8408
static const u16	crc16_check = 0x0f47

Detailed Description

Definition at line 27 of file hdlc.h.

Constructor & Destructor Documentation

hdlc_dec()

leansdr::hdlc_dec::hdlc_dec ( int  _minframesize, int  _maxframesize, bool  _invert  )

inline

Definition at line 30 of file hdlc.h.

References reset().

Referenced by leansdr::hdlc_sync::hdlc_sync().

                           : minframesize(_minframesize),
                             maxframesize(_maxframesize),
                             invertmask(_invert ? 0xff : 0),
                             framebuf(new u8[maxframesize]),
                             debug(false)
    {
        reset();
    }

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Member Function Documentation

begin_frame()

void leansdr::hdlc_dec::begin_frame ( )

inline

Definition at line 47 of file hdlc.h.

References crc16, crc16_init, and framesize.

Referenced by decode().

    {
        framesize = 0;
        crc16 = crc16_init;
    }

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crc16_byte()

void leansdr::hdlc_dec::crc16_byte ( u8  data )

inlineprivate

Definition at line 180 of file hdlc.h.

References crc16_poly.

Referenced by decode().

    {
        crc16 ^= data;

        for (int bit = 8; bit--;)
        {
            crc16 = (crc16 & 1) ? (crc16 >> 1) ^ crc16_poly : (crc16 >> 1);
        }
    }

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decode()

u8* leansdr::hdlc_dec::decode ( u8 **  ppin, int  count, int *  pdatasize, int *  hdlc_errors, int *  fcs_errors  )

inline

Definition at line 59 of file hdlc.h.

References begin_frame(), byte_out, crc16, crc16_byte(), crc16_check, debug, framebuf, framesize, inframe, invertmask, maxframesize, minframesize, nbits_out, and shiftreg.

    {
        *hdlc_errors = 0;
        *fcs_errors = 0;
        *pdatasize = -1;
        u8 *pin = *ppin, *pend = pin + count;

        for (; pin < pend; ++pin)
        {
            u8 byte_in = (*pin) ^ invertmask;

            for (int bits = 8; bits--; byte_in <<= 1)
            {
                u8 bit_in = byte_in & 128;
                shiftreg = (shiftreg >> 1) | bit_in;

                if (!inframe)
                {
                    if (shiftreg == 0x7e)
                    { // HDLC flag 01111110
                        inframe = true;
                        nbits_out = 0;
                        begin_frame();
                    }
                }
                else
                {
                    if ((shiftreg & 0xfe) == 0x7c)
                    { // 0111110x HDLC stuffing
                        // Unstuff this 0
                    }
                    else if (shiftreg == 0x7e)
                    { // 01111110 HDLC flag
                        if (nbits_out != 7)
                        {
                            // Not at byte boundary
                            if (debug)
                                fprintf(stderr, "^");
                            ++*hdlc_errors;
                        }
                        else
                        {
                            // Checksum
                            crc16 ^= 0xffff;
                            if (framesize < 2 || framesize < minframesize || crc16 != crc16_check)
                            {
                                if (debug)
                                    fprintf(stderr, "!");
                                ++*hdlc_errors;
                                // Do not report random noise as FCS errors
                                if (framesize >= minframesize)
                                    ++*fcs_errors;
                            }
                            else
                            {
                                if (debug)
                                    fprintf(stderr, "_");
                                // This will trigger output, but we finish the byte first.
                                *pdatasize = framesize - 2;
                            }
                        }
                        nbits_out = 0;
                        begin_frame();
                        // Keep processing up to 7 remaining bits from byte_in.
                        // Special cases 0111111 and 1111111 cannot affect *pdatasize.
                    }
                    else if (shiftreg == 0xfe)
                    { // 11111110 HDLC invalid
                        if (framesize)
                        {
                            if (debug)
                                fprintf(stderr, "^");
                            ++*hdlc_errors;
                        }
                        inframe = false;
                    }
                    else
                    {                                        // Data bit
                        byte_out = (byte_out >> 1) | bit_in; // HDLC is LSB first
                        ++nbits_out;
                        if (nbits_out == 8)
                        {
                            if (framesize < maxframesize)
                            {
                                framebuf[framesize++] = byte_out;
                                crc16_byte(byte_out);
                            }
                            nbits_out = 0;
                        }
                    }
                } // inframe
            }     // bits
            if (*pdatasize != -1)
            {
                // Found a complete frame
                *ppin = pin + 1;
                return framebuf;
            }
        }

        *ppin = pin;
        return NULL;
    }

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reset()

void leansdr::hdlc_dec::reset ( )

inline

Definition at line 41 of file hdlc.h.

References inframe, and shiftreg.

Referenced by hdlc_dec().

    {
        shiftreg = 0;
        inframe = false;
    }

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Member Data Documentation

byte_out

u8 leansdr::hdlc_dec::byte_out

private

Definition at line 171 of file hdlc.h.

Referenced by decode().

crc16

u16 leansdr::hdlc_dec::crc16

private

Definition at line 174 of file hdlc.h.

Referenced by begin_frame(), and decode().

crc16_check

const u16 leansdr::hdlc_dec::crc16_check = 0x0f47

staticprivate

Definition at line 178 of file hdlc.h.

Referenced by decode().

crc16_init

const u16 leansdr::hdlc_dec::crc16_init = 0xffff

staticprivate

Definition at line 176 of file hdlc.h.

Referenced by begin_frame().

crc16_poly

const u16 leansdr::hdlc_dec::crc16_poly = 0x8408

staticprivate

Definition at line 177 of file hdlc.h.

Referenced by crc16_byte().

debug

bool leansdr::hdlc_dec::debug

Definition at line 191 of file hdlc.h.

Referenced by decode().

framebuf

u8* leansdr::hdlc_dec::framebuf

private

Definition at line 167 of file hdlc.h.

Referenced by decode().

framesize

int leansdr::hdlc_dec::framesize

private

Definition at line 173 of file hdlc.h.

Referenced by begin_frame(), and decode().

inframe

bool leansdr::hdlc_dec::inframe

private

Definition at line 170 of file hdlc.h.

Referenced by decode(), and reset().

invertmask

u8 leansdr::hdlc_dec::invertmask

private

Definition at line 166 of file hdlc.h.

Referenced by decode().

maxframesize

int leansdr::hdlc_dec::maxframesize

private

Definition at line 165 of file hdlc.h.

Referenced by decode(), leansdr::hdlc_sync::hdlc_sync(), and leansdr::hdlc_sync::run().

minframesize

int leansdr::hdlc_dec::minframesize

private

Definition at line 165 of file hdlc.h.

Referenced by decode(), and leansdr::hdlc_sync::hdlc_sync().

nbits_out

int leansdr::hdlc_dec::nbits_out

private

Definition at line 172 of file hdlc.h.

Referenced by decode().

shiftreg

u8 leansdr::hdlc_dec::shiftreg

private

Definition at line 169 of file hdlc.h.

Referenced by decode(), and reset().

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The documentation for this struct was generated from the following file:

• plugins/channelrx/demoddatv/leansdr/hdlc.h