mirror of
https://github.com/f4exb/sdrangel.git
synced 2024-11-16 21:31:47 -05:00
59 lines
1.5 KiB
C
59 lines
1.5 KiB
C
|
#ifndef LEANSDR_IESS_H
|
||
|
|
#define LEANSDR_IESS_H
|
||
|
|
|
||
|
|
#include "leansdr/framework.h"
|
||
|
|
|
||
|
|
namespace leansdr {
|
||
|
|
|
||
|
|
// SELF-SYNCHRONIZING DESCRAMBLER
|
||
|
|
// Per ETSI TR 192 figure 8 (except Q20/ not connected to CLOCK).
|
||
|
|
// This implementation operates on packed bits, MSB first.
|
||
|
|
|
||
|
|
struct etr192_descrambler : runnable {
|
||
|
|
etr192_descrambler(scheduler *sch,
|
||
|
|
pipebuf<u8> &_in, // Packed scrambled bits
|
||
|
|
pipebuf<u8> &_out) // Packed bits
|
||
|
|
: runnable(sch, "etr192_dec"),
|
||
|
|
in(_in), out(_out),
|
||
|
|
shiftreg(0), counter(0)
|
||
|
|
{
|
||
|
|
}
|
||
|
|
|
||
|
|
void run() {
|
||
|
|
int count = min(in.readable(), out.writable());
|
||
|
|
for ( u8 *pin=in.rd(), *pend=pin+count, *pout=out.wr();
|
||
|
|
pin<pend; ++pin,++pout) {
|
||
|
|
u8 byte_in=*pin, byte_out=0;
|
||
|
|
for ( int b=8; b--; byte_in<<=1 ) {
|
||
|
|
// Levels before clock transition
|
||
|
|
int bit_in = (byte_in&128) ? 1 : 0;
|
||
|
|
int reset_counter = (shiftreg ^ (shiftreg>>8)) & 1;
|
||
|
|
int counter_overflow = (counter==31) ? 1 : 0;
|
||
|
|
int taps = (shiftreg>>2) ^ (shiftreg>>19);
|
||
|
|
int bit_out = (taps ^ counter_overflow ^ bit_in ^ 1) & 1;
|
||
|
|
// Execute clock transition
|
||
|
|
#if 1 // Descramble
|
||
|
|
shiftreg = (shiftreg<<1) | bit_in;
|
||
|
|
#else // Scramble
|
||
|
|
shiftreg = (shiftreg<<1) | bit_out;
|
||
|
|
#endif
|
||
|
|
counter = reset_counter ? 0 : (counter+1)&31;
|
||
|
|
byte_out = (byte_out<<1) | bit_out;
|
||
|
|
}
|
||
|
|
*pout = byte_out;
|
||
|
|
}
|
||
|
|
in.read(count);
|
||
|
|
out.written(count);
|
||
|
|
}
|
||
|
|
|
||
|
|
private:
|
||
|
|
pipereader<u8> in;
|
||
|
|
pipewriter<u8> out;
|
||
|
|
u32 shiftreg; // 20 bits
|
||
|
|
u8 counter; // 5 bits
|
||
|
|
}; // etr192_descrambler
|
||
|
|
|
||
|
|
} // namespace
|
||
|
|
|
||
|
|
#endif // LEANSDR_IESS_H
|