Updated documentation
This commit is contained in:
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@ -7,13 +7,29 @@
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#include "compression/heatshrink_encoder.h"
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#include "compression/heatshrink_decoder.h"
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// FIXME: Describe these
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static uint8_t lastByte = 0x00;
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// We need an indicator to tell us whether we
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// should send a parity byte. This happens
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// whenever two normal bytes of data has been
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// sent. We also keep the last sent byte in
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// memory because we need it to calculate the
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// parity byte.
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static bool sendParityBlock = false;
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static uint8_t lastByte = 0x00;
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// We also need a buffer for compressing and
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// decompressing packet data.
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static uint8_t compressionBuffer[MP1_MAX_FRAME_LENGTH+10];
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// FIXME: Describe this
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// The GET_BIT macro is used in the interleaver
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// and deinterleaver to access single bits of a
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// byte.
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INLINE bool GET_BIT(uint8_t byte, int n) { return (byte & (1 << (8-n))) == (1 << (8-n)); }
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// This function calculates and returns a parity
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// byte for two input bytes. The parity byte is
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// used for correcting errors in the transmission.
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// The error correction algorithm is a standard
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// (12,8) Hamming code.
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INLINE bool BIT(uint8_t byte, int n) { return ((byte & BV(n-1))>>(n-1)); }
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static uint8_t mp1ParityBlock(uint8_t first, uint8_t other) {
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uint8_t parity = 0x00;
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@ -31,11 +47,14 @@ static uint8_t mp1ParityBlock(uint8_t first, uint8_t other) {
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return parity;
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}
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// This deode function retrieves the buffer of
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// received, deinterleaved and error-corrected
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// bytes, inspects the header and determines
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// whether there is padding to be removed, and
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// whether the packet is compressed. If it is
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// it is decompressed before being passed to
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// the registered callback.
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static void mp1Decode(MP1 *mp1) {
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// This decode function is basic and bare minimum.
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// It does nothing more than extract the data
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// payload from the buffer and put it into a struct
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// for further processing.
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MP1Packet packet; // A decoded packet struct
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uint8_t *buffer = mp1->buffer; // Get the buffer from the protocol context
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@ -55,11 +74,14 @@ static void mp1Decode(MP1 *mp1) {
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// Check if we have received a compressed packet
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if (header & MP1_HEADER_COMPRESSION) {
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// If we have, we decompress it and use the
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// decompressed data for the packet
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size_t decompressedSize = decompress(buffer, packet.dataLength);
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packet.dataLength = decompressedSize;
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memcpy(buffer, compressionBuffer, decompressedSize);
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}
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// Set the data field of the packet to our buffer
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packet.data = buffer;
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// If a callback have been specified, let's
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@ -67,43 +89,6 @@ static void mp1Decode(MP1 *mp1) {
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if (mp1->callback) mp1->callback(&packet);
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}
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// Interleaved:
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// abcabcab cabcabca bcabcabc
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// 11144477 22255578 63336688
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//
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// 0 1 2
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static void mp1Deinterleave(MP1 *mp1) {
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uint8_t a = (GET_BIT(mp1->interleaveIn[0], 1) << 7) +
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(GET_BIT(mp1->interleaveIn[1], 2) << 6) +
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(GET_BIT(mp1->interleaveIn[2], 3) << 5) +
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(GET_BIT(mp1->interleaveIn[0], 4) << 4) +
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(GET_BIT(mp1->interleaveIn[1], 5) << 3) +
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(GET_BIT(mp1->interleaveIn[2], 6) << 2) +
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(GET_BIT(mp1->interleaveIn[0], 7) << 1) +
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(GET_BIT(mp1->interleaveIn[1], 8));
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uint8_t b = (GET_BIT(mp1->interleaveIn[0], 2) << 7) +
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(GET_BIT(mp1->interleaveIn[1], 3) << 6) +
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(GET_BIT(mp1->interleaveIn[2], 4) << 5) +
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(GET_BIT(mp1->interleaveIn[0], 5) << 4) +
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(GET_BIT(mp1->interleaveIn[1], 6) << 3) +
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(GET_BIT(mp1->interleaveIn[2], 1) << 2) +
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(GET_BIT(mp1->interleaveIn[0], 8) << 1) +
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(GET_BIT(mp1->interleaveIn[2], 7));
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uint8_t c = (GET_BIT(mp1->interleaveIn[0], 3) << 7) +
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(GET_BIT(mp1->interleaveIn[1], 1) << 6) +
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(GET_BIT(mp1->interleaveIn[2], 2) << 5) +
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(GET_BIT(mp1->interleaveIn[0], 6) << 4) +
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(GET_BIT(mp1->interleaveIn[1], 4) << 3) +
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(GET_BIT(mp1->interleaveIn[2], 5) << 2) +
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(GET_BIT(mp1->interleaveIn[1], 7) << 1) +
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(GET_BIT(mp1->interleaveIn[2], 8));
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mp1->interleaveIn[0] = a;
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mp1->interleaveIn[1] = b;
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mp1->interleaveIn[2] = c;
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}
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////////////////////////////////////////////////////////////
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// The Poll function reads data from the modem, handles //
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while ((byte = kfile_getc(mp1->modem)) != EOF) {
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// We have a byte, increment our read counter
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// FIXME: Describe error correction
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/////////////////////////////////////////////
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// This following block handles forward //
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// error correction using an interleaved //
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// (12,8) Hamming code //
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/////////////////////////////////////////////
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// If we have started reading (received an
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// HDLC_FLAG), we will start looking at the
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// incoming data and perform forward error
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// correction on it.
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if (mp1->reading && (byte != AX25_ESC) ) {
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mp1->readLength++;
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// Check if we have read three bytes. If we
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// have, we should now have a block of two
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// data bytes and a parity byte. This block
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if (mp1->readLength % 3 == 0) {
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// Put bytes in deinterleave buffer
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// The block is interleaved, so we will
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// first put the received bytes in the
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// deinterleaving buffer
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mp1->interleaveIn[0] = mp1->buffer[mp1->packetLength-2];
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mp1->interleaveIn[1] = mp1->buffer[mp1->packetLength-1];
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mp1->interleaveIn[2] = byte;
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// We then deinterleave the block
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mp1Deinterleave(mp1);
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// And write the deinterleaved data
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// back into the buffer
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mp1->buffer[mp1->packetLength-2] = mp1->interleaveIn[0];
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mp1->buffer[mp1->packetLength-1] = mp1->interleaveIn[1];
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// We now calculate a parity byte on the
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// received data.
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mp1->calculatedParity = mp1ParityBlock(mp1->buffer[mp1->packetLength-2], mp1->buffer[mp1->packetLength-1]);
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// By XORing the calculated parity byte
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// with the received parity byte, we get
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// what is called the "syndrome". This
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// number will tell us if we had any
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// errors during transmission, and if so
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// where they are. Using Hamming code, we
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// can only detect single bit errors in a
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// byte though, which is why we interleave
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// the data, since most errors will usually
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// occur in bursts of more than one bit.
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// With 2 data byte interleaving we can
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// correct 2 consecutive bit errors.
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uint8_t syndrome = mp1->calculatedParity ^ mp1->interleaveIn[2];
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if (syndrome == 0x00) {
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// No problems!
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// If the syndrome equals 0, we either
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// don't have any errors, or the error
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// is unrecoverable, so we don't do
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// anything
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} else {
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// If the syndrome is not equal to 0,
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// there is a problem, and we will try
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// to correct it. We first need to split
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// the syndrome byte up into the two
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// actual syndrome numbers, one for
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// each data byte.
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uint8_t syndromes[2];
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syndromes[0] = syndrome & 0x0f;
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syndromes[1] = (syndrome & 0xf0) >> 4;
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// Then we look at each syndrome number
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// to determine what bit in the data
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// bytes to correct.
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for (int i = 0; i < 2; i++) {
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uint8_t s = syndromes[i];
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uint8_t correction = 0x00;
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if (s == 1 || s == 2 || s == 4 || s == 8) {
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// Error in parity bit, no correction needed
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// This signifies an error in the
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// parity block, so we actually
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// don't need any correction
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continue;
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}
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// The following determines what
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// bit to correct according to
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// the syndrome value.
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if (s == 3) correction = 0x01;
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if (s == 5) correction = 0x02;
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if (s == 6) correction = 0x04;
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if (s == 11) correction = 0x40;
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if (s == 12) correction = 0x80;
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// And finally we apply the correction
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mp1->buffer[mp1->packetLength-(2-i)] ^= correction;
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// This is just for testing purposes.
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// Nice to know when corrections were
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// actually made.
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if (s != 0) mp1->correctionsMade += 1;
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}
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}
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// We now update the checksum of the packet
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// with the deinterleaved and possibly
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// corrected bytes.
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mp1->checksum_in ^= mp1->buffer[mp1->packetLength-2];
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mp1->checksum_in ^= mp1->buffer[mp1->packetLength-1];
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//mp1->checksum_in ^= mp1->interleaveIn[2];
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continue;
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}
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}
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// FIXME: Describe error correction //////////
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/////////////////////////////////////////////
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// End of forward error correction block //
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/////////////////////////////////////////////
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// This next part of the poll function handles
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// the reading from the modem, and looks for
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// starts and ends of transmissions. It also
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// handles escape characters by discarding them
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// so they don't get put into the output data.
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// Let's first check if we have read an HDLC_FLAG.
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if (!mp1->escape && byte == HDLC_FLAG) {
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// We are not in an escape sequence and we
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// found a HDLC_FLAG. This can mean two things:
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continue;
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}
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// This should be a parity byte
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if (!mp1->escape && byte == AX25_ESC) {
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// We found an escape character. We'll set
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// the escape seqeunce indicator so we don't
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// interpret the next byte as a reset or flag
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mp1->escape = true;
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// We then continue reading the next byte.
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continue;
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}
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if (mp1->packetLength < MP1_MAX_FRAME_LENGTH) {
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// If the length of the current incoming frame is
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// still less than our max length, put the incoming
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// byte in the buffer.
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// mp1->checksum_in = mp1->checksum_in ^ byte;
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// byte in the buffer. When we have collected 3
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// bytes, they will be processed by the error
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// correction part above.
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mp1->buffer[mp1->packetLength++] = byte;
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} else {
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// If not, we have a problem: The buffer has overrun
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@ -268,6 +319,162 @@ static void mp1WriteByte(MP1 *mp1, uint8_t byte) {
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kfile_putc(byte, mp1->modem);
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}
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// This is an intermediary function that
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// receives outgoing bytes, and adds
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// interleaving and a parity byte to the
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// outgoing data in blocks of two data
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// bytes. The actual transmitted block will
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// be 3 bytes long due to the added parity
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// byte.
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static void mp1Putbyte(MP1 *mp1, uint8_t byte) {
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mp1Interleave(mp1, byte);
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if (sendParityBlock) {
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uint8_t p = mp1ParityBlock(lastByte, byte);
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//kfile_putc(p, mp1->modem);
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mp1Interleave(mp1, p);
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}
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lastByte = byte;
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sendParityBlock ^= true;
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}
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// This function accepts a buffer with data
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// to be transmitted, and structures it into
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// a valid packet.
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void mp1Send(MP1 *mp1, const void *_buffer, size_t length) {
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// Get the transmit data buffer
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const uint8_t *buffer = (const uint8_t *)_buffer;
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// Initialize checksum to zero
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mp1->checksum_out = MP1_CHECKSUM_INIT;
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// We also reset the interleave counter to zero
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mp1->interleaveCounter = 0;
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// Transmit the HDLC_FLAG to signify start of TX
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kfile_putc(HDLC_FLAG, mp1->modem);
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// We start out assuming we should not use
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// compression.
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bool packetCompression = false;
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// We then try to compress the data to see
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// if we can save some space with compression.
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size_t compressedSize = compress(buffer, length);
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if (compressedSize != 0 && compressedSize < length) {
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// Compression saved us some space, we'll
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// send the paket compressed
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packetCompression = true;
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// Write the compressed data into the
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// outgoing data buffer
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memcpy(buffer, compressionBuffer, compressedSize);
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// Make sure to set the length of the
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// data to the new (compressed) length
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length = compressedSize;
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} else {
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// We are not going to use compression,
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// so we don't do anything.
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}
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// We now need to construct a header, that
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// can tell the receiving end whether the
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// packet is compressed. Since a packet must
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// have an even number of total payload bytes
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// (including the header), we check the length
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// of the outgoing data, and if it is not even,
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// we add a single byte of padding to the
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// packet. Remember that we also send a single
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// byte checksum at the end of the packet, so
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// the header and checksum bytes together don't
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// change whether the payload length is even
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// or not. The payload length needs to be even
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// since we are sending a parity byte for every
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// two data bytes sent, and because interleaving
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// happens in blocks of three bytes.
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uint8_t header = 0xf0;
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// If we are using compression, set the
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// appropriate header flag to true.
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if (packetCompression) header ^= MP1_HEADER_COMPRESSION;
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// We check if the data length is even
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if (length % 2 != 0) {
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// If it is not, we set the appropriate
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// header flag to indicate that we are
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// padding this packet with one byte.
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header ^= MP1_HEADER_PADDED;
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// We then update the checksum with the
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// header byte and queue it for transmit
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mp1->checksum_out = mp1->checksum_out ^ header;
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mp1Putbyte(mp1, header);
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// We now update the checksum with the
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// padding byte, and queue that for
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// transmission as well. At this point,
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// we will have pushed out two bytes of
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// data. The output function will detect
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// this, and a parity byte will be
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// calculated. The 3-byte block is then
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// actually transmitted.
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mp1->checksum_out = mp1->checksum_out ^ MP1_PADDING;
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mp1Putbyte(mp1, MP1_PADDING);
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} else {
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// If the length was already even, we
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// just update the checksum with the
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// header byte and queue it.
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mp1->checksum_out = mp1->checksum_out ^ header;
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mp1Putbyte(mp1, header);
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}
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// Now we'll transmit the actual data of
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// the packet. We continously increment the
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// pointer address of the buffer while
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// passing it to the intermediary output
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// function. Everytime the interleaving
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// counter reaches 3, a block will be
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// transmitted.
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while (length--) {
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mp1->checksum_out = mp1->checksum_out ^ *buffer;
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mp1Putbyte(mp1, *buffer++);
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}
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// Finally we write the checksum to the
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// end of the packet.
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mp1Putbyte(mp1, mp1->checksum_out);
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// And transmit a HDLC_FLAG to signify
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// end of the transmission.
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kfile_putc(HDLC_FLAG, mp1->modem);
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}
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// This function will simply initialize
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// the protocol context and allocate the
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// needed memory.
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void mp1Init(MP1 *mp1, KFile *modem, mp1_callback_t callback) {
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// Allocate memory for our protocol "object"
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memset(mp1, 0, sizeof(*mp1));
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// Set references to our modem "object" and
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// a callback for when a packet has been decoded
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mp1->modem = modem;
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mp1->callback = callback;
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}
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// A handy debug function that can determine
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// how much available memory we have left.
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int freeRam(void) {
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extern int __heap_start, *__brkval;
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int v;
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return (int) &v - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
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}
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// Following is the functions responsible
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// for interleaving and deinterleaving
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// blocks of data. The interleaving table
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// is also included.
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///////////////////////////////
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// Interleave-table //
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///////////////////////////////
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@ -310,7 +517,7 @@ static void mp1WriteByte(MP1 *mp1, uint8_t byte) {
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//
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///////////////////////////////
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static void mp1Interleave(MP1 *mp1, uint8_t byte) {
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void mp1Interleave(MP1 *mp1, uint8_t byte) {
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mp1->interleaveOut[mp1->interleaveCounter] = byte;
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mp1->interleaveCounter++;
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if (mp1->interleaveCounter == 3) {
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@ -355,94 +562,42 @@ static void mp1Interleave(MP1 *mp1, uint8_t byte) {
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}
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}
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// FIXME: Desribe additions here
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static void mp1Putbyte(MP1 *mp1, uint8_t byte) {
|
||||
//kfile_putc(byte, mp1->modem);
|
||||
mp1Interleave(mp1, byte);
|
||||
|
||||
if (sendParityBlock) {
|
||||
uint8_t p = mp1ParityBlock(lastByte, byte);
|
||||
//kfile_putc(p, mp1->modem);
|
||||
mp1Interleave(mp1, p);
|
||||
}
|
||||
void mp1Deinterleave(MP1 *mp1) {
|
||||
uint8_t a = (GET_BIT(mp1->interleaveIn[0], 1) << 7) +
|
||||
(GET_BIT(mp1->interleaveIn[1], 2) << 6) +
|
||||
(GET_BIT(mp1->interleaveIn[2], 3) << 5) +
|
||||
(GET_BIT(mp1->interleaveIn[0], 4) << 4) +
|
||||
(GET_BIT(mp1->interleaveIn[1], 5) << 3) +
|
||||
(GET_BIT(mp1->interleaveIn[2], 6) << 2) +
|
||||
(GET_BIT(mp1->interleaveIn[0], 7) << 1) +
|
||||
(GET_BIT(mp1->interleaveIn[1], 8));
|
||||
|
||||
lastByte = byte;
|
||||
sendParityBlock ^= true;
|
||||
}
|
||||
|
||||
void mp1Send(MP1 *mp1, const void *_buffer, size_t length) {
|
||||
// Get the transmit data buffer
|
||||
const uint8_t *buffer = (const uint8_t *)_buffer;
|
||||
|
||||
// Initialize checksum
|
||||
mp1->checksum_out = MP1_CHECKSUM_INIT;
|
||||
mp1->interleaveCounter = 0; // FIXME:
|
||||
|
||||
// Transmit the HDLC_FLAG to signify start of TX
|
||||
kfile_putc(HDLC_FLAG, mp1->modem);
|
||||
|
||||
bool packetCompression = false;
|
||||
size_t compressedSize = compress(buffer, length);
|
||||
if (compressedSize != 0 && compressedSize < length) {
|
||||
// Compression saved us some space, we'll
|
||||
// send the paket compressed
|
||||
packetCompression = true;
|
||||
memcpy(buffer, compressionBuffer, compressedSize);
|
||||
length = compressedSize;
|
||||
} else {
|
||||
// We are not going to use compression
|
||||
}
|
||||
|
||||
// Write header and possibly padding
|
||||
// Remember we also write a header and
|
||||
// a checksum. This ensures that we will
|
||||
// always end our packet with a checksum
|
||||
// and a parity byte.
|
||||
|
||||
uint8_t header = 0xf0;
|
||||
if (packetCompression) header ^= MP1_HEADER_COMPRESSION;
|
||||
|
||||
if (length % 2 != 0) {
|
||||
header ^= MP1_HEADER_PADDED;
|
||||
mp1->checksum_out = mp1->checksum_out ^ header;
|
||||
mp1Putbyte(mp1, header);
|
||||
mp1->checksum_out = mp1->checksum_out ^ MP1_PADDING;
|
||||
mp1Putbyte(mp1, MP1_PADDING);
|
||||
} else {
|
||||
mp1->checksum_out = mp1->checksum_out ^ header;
|
||||
mp1Putbyte(mp1, header);
|
||||
}
|
||||
|
||||
// Continously increment the pointer address
|
||||
// of the buffer while passing it to the byte
|
||||
// output function
|
||||
while (length--) {
|
||||
mp1->checksum_out = mp1->checksum_out ^ *buffer;
|
||||
mp1Putbyte(mp1, *buffer++);
|
||||
}
|
||||
|
||||
// Write checksum to end of packet
|
||||
mp1Putbyte(mp1, mp1->checksum_out);
|
||||
|
||||
// Transmit a HDLC_FLAG to signify end of TX
|
||||
kfile_putc(HDLC_FLAG, mp1->modem);
|
||||
}
|
||||
|
||||
void mp1Init(MP1 *mp1, KFile *modem, mp1_callback_t callback) {
|
||||
// Allocate memory for our protocol "object"
|
||||
memset(mp1, 0, sizeof(*mp1));
|
||||
// Set references to our modem "object" and
|
||||
// a callback for when a packet has been decoded
|
||||
mp1->modem = modem;
|
||||
mp1->callback = callback;
|
||||
}
|
||||
|
||||
int freeRam(void) {
|
||||
extern int __heap_start, *__brkval;
|
||||
int v;
|
||||
return (int) &v - (__brkval == 0 ? (int) &__heap_start : (int) __brkval);
|
||||
uint8_t b = (GET_BIT(mp1->interleaveIn[0], 2) << 7) +
|
||||
(GET_BIT(mp1->interleaveIn[1], 3) << 6) +
|
||||
(GET_BIT(mp1->interleaveIn[2], 4) << 5) +
|
||||
(GET_BIT(mp1->interleaveIn[0], 5) << 4) +
|
||||
(GET_BIT(mp1->interleaveIn[1], 6) << 3) +
|
||||
(GET_BIT(mp1->interleaveIn[2], 1) << 2) +
|
||||
(GET_BIT(mp1->interleaveIn[0], 8) << 1) +
|
||||
(GET_BIT(mp1->interleaveIn[2], 7));
|
||||
|
||||
uint8_t c = (GET_BIT(mp1->interleaveIn[0], 3) << 7) +
|
||||
(GET_BIT(mp1->interleaveIn[1], 1) << 6) +
|
||||
(GET_BIT(mp1->interleaveIn[2], 2) << 5) +
|
||||
(GET_BIT(mp1->interleaveIn[0], 6) << 4) +
|
||||
(GET_BIT(mp1->interleaveIn[1], 4) << 3) +
|
||||
(GET_BIT(mp1->interleaveIn[2], 5) << 2) +
|
||||
(GET_BIT(mp1->interleaveIn[1], 7) << 1) +
|
||||
(GET_BIT(mp1->interleaveIn[2], 8));
|
||||
|
||||
mp1->interleaveIn[0] = a;
|
||||
mp1->interleaveIn[1] = b;
|
||||
mp1->interleaveIn[2] = c;
|
||||
}
|
||||
|
||||
// This function compresses data using
|
||||
// the Heatshrink library
|
||||
size_t compress(uint8_t *input, size_t length) {
|
||||
heatshrink_encoder *hse = heatshrink_encoder_alloc(8, 4);
|
||||
if (hse == NULL) {
|
||||
|
@ -467,6 +622,8 @@ size_t compress(uint8_t *input, size_t length) {
|
|||
return written;
|
||||
}
|
||||
|
||||
// This function decompresses data using
|
||||
// the Heatshrink library
|
||||
size_t decompress(uint8_t *input, size_t length) {
|
||||
heatshrink_decoder *hsd = heatshrink_decoder_alloc(MP1_MAX_FRAME_LENGTH, 8, 4);
|
||||
if (hsd == NULL) {
|
||||
|
|
|
@ -15,15 +15,14 @@
|
|||
#define HDLC_RESET 0x7F
|
||||
#define AX25_ESC 0x1B
|
||||
|
||||
// Some further definitions FIXME:
|
||||
// We also define a few header flags and what
|
||||
// to send as padding if we need to pad a
|
||||
// packet. Due to forward error correction,
|
||||
// packets must have an even number of bytes.
|
||||
#define MP1_PADDING 0x55
|
||||
#define MP1_HEADER_PADDED 0x01
|
||||
#define MP1_HEADER_COMPRESSION 0x02
|
||||
|
||||
// FIXME: describe
|
||||
//static uint8_t compressedData[MP1_MAX_FRAME_LENGTH-0];
|
||||
static uint8_t compressionBuffer[MP1_MAX_FRAME_LENGTH+10];
|
||||
|
||||
// Just a forward declaration that this struct exists
|
||||
struct MP1Packet;
|
||||
|
||||
|
@ -44,11 +43,10 @@ typedef struct MP1 {
|
|||
uint8_t checksum_out; // Rolling checksum for outgoing packets
|
||||
bool reading; // True when we have seen a HDLC flag
|
||||
bool escape; // We need to know if we are in an escape sequence
|
||||
bool fecEscape; // fec escape
|
||||
long correctionsMade; // correction count
|
||||
uint8_t interleaveCounter; // interleave counter
|
||||
uint8_t interleaveOut[MP1_INTERLEAVE_SIZE];
|
||||
uint8_t interleaveIn[MP1_INTERLEAVE_SIZE];
|
||||
long correctionsMade; // A counter for how many corrections were made to a packet
|
||||
uint8_t interleaveCounter; // Keeps track of when we have received an entire interleaved block
|
||||
uint8_t interleaveOut[MP1_INTERLEAVE_SIZE]; // A buffer for interleaving bytes before they are sent
|
||||
uint8_t interleaveIn[MP1_INTERLEAVE_SIZE]; // A buffer for storing interleaved bytes before they are deinterleaved
|
||||
} MP1;
|
||||
|
||||
// A struct encapsulating a network packet
|
||||
|
@ -57,6 +55,7 @@ typedef struct MP1Packet {
|
|||
size_t dataLength; // The length of the received data
|
||||
} MP1Packet;
|
||||
|
||||
// Declarations of functions
|
||||
void mp1Init(MP1 *mp1, KFile *modem, mp1_callback_t callback);
|
||||
void mp1Read(MP1 *mp1, int byte);
|
||||
void mp1Poll(MP1 *mp1);
|
||||
|
@ -65,5 +64,7 @@ void mp1Send(MP1 *mp1, const void *_buffer, size_t length);
|
|||
int freeRam(void);
|
||||
size_t compress(uint8_t *input, size_t length);
|
||||
size_t decompress(uint8_t *input, size_t length);
|
||||
void mp1Deinterleave(MP1 *mp1);
|
||||
void mp1Interleave(MP1 *mp1, uint8_t byte);
|
||||
|
||||
#endif
|
|
@ -1,2 +1,2 @@
|
|||
#define VERS_BUILD 1197
|
||||
#define VERS_BUILD 1206
|
||||
#define VERS_HOST "vixen"
|
||||
|
|
Loading…
Reference in New Issue