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#include <iostream>
#include "snap_packet.h"
#include "snap.h"
SNAPPacket::SNAPPacket()
{
sync = 0x54;
hdb2 = 0x51;
hdb1 = 0x30;
dab = 0;
sab = 0;
crc = 0;
}
bool SNAPPacket::readPacket(SNAP &snap)
{
crc = 0;
byte actualCRC;
try {
for(;;) {
sync = snap.readbyte();
if (sync == 0x54) break;
}
hdb2 = computeCRC(snap.readbyte());
hdb1 = computeCRC(snap.readbyte());
dab = computeCRC(snap.readbyte());
sab = computeCRC(snap.readbyte());
for(int i = 0; i < getLength(); i++) {
payload[i] = computeCRC(snap.readbyte());
}
actualCRC = snap.readbyte();
} catch(SNAPTimeoutException) {
std::cerr << "Timeout waiting for receive" << std::endl;
return false;
}
if (crc != actualCRC) {
std::cerr << "CRC fail, got " << (int)actualCRC << " expected " << (int)crc
<< std::endl;
crc = actualCRC;
return false;
}
return true;
}
SNAPPacket SNAPPacket::reply()
{
SNAPPacket p;
p.dab = sab;
p.sab = dab;
return p;
}
bool SNAPPacket::send(SNAP &snap, bool verbose)
{
for(int retries = 0; retries < 5; retries++) {
crc = 0;
snap.sendbyte(sync);
snap.sendbyte(computeCRC(hdb2));
snap.sendbyte(computeCRC(hdb1));
snap.sendbyte(computeCRC(dab));
snap.sendbyte(computeCRC(sab));
for(int i = 0; i < getLength(); i++) {
snap.sendbyte(computeCRC(payload[i]));
}
snap.sendbyte(crc);
SNAPPacket p;
if (!p.readPacket(snap)) {
std::cerr << "Read fail 1" << std::endl;
continue;
}
if (p.isAck()) {
if (verbose)
std::cout << "[ACK Received]" << std::endl;
return true;
}
if (p.isNak()) {
std::cerr << "Got NAK" << std::endl;
continue;
}
std::cerr << "Read fail 2" << std::endl;
}
return false;
}
byte SNAPPacket::computeCRC(byte dataval)
{
byte i = dataval ^ crc;
crc = 0;
if(i & 1)
crc ^= 0x5e;
if(i & 2)
crc ^= 0xbc;
if(i & 4)
crc ^= 0x61;
if(i & 8)
crc ^= 0xc2;
if(i & 0x10)
crc ^= 0x9d;
if(i & 0x20)
crc ^= 0x23;
if(i & 0x40)
crc ^= 0x46;
if(i & 0x80)
crc ^= 0x8c;
return dataval;
}
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