Osmocom GSM/GPRS/EGPRS transceiver, originally forked from OpenBTS transceiver. For building SDR based GSM BTS with osmo-bts-trx.
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osmo-trx/CommonLibs/PRBS.h

108 lines
2.8 KiB

/*
* Copyright (C) 2017 Alexander Chemeris <Alexander.Chemeris@fairwaves.co>
*
* SPDX-License-Identifier: LGPL-2.1+
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*/
#ifndef PRBS_H
#define PRBS_H
#include <stdint.h>
#include <assert.h>
/** Pseudo-random binary sequence (PRBS) generator (a Galois LFSR implementation). */
class PRBS {
public:
PRBS(unsigned wLen, uint64_t wCoeff, uint64_t wState = 0x01)
: mCoeff(wCoeff), mStartState(wState), mState(wState), mLen(wLen)
{ assert(wLen<=64); }
/**@name Accessors */
//@{
uint64_t coeff() const { return mCoeff; }
uint64_t state() const { return mState; }
void state(uint64_t state) { mState = state & mask(); }
unsigned size() const { return mLen; }
//@}
/**
Calculate one bit of a PRBS
*/
unsigned generateBit()
{
const unsigned result = mState & 0x01;
processBit(result);
return result;
}
/**
Update the generator state by one bit.
If you want to synchronize your PRBS to a known state, call this function
size() times passing your PRBS to it bit by bit.
*/
void processBit(unsigned inBit)
{
mState >>= 1;
if (inBit) mState ^= mCoeff;
}
/** Return true when PRBS is wrapping through initial state */
bool isFinished() const { return mStartState == mState; }
protected:
uint64_t mCoeff; ///< polynomial coefficients. LSB is zero exponent.
uint64_t mStartState; ///< initial shift register state.
uint64_t mState; ///< shift register state.
unsigned mLen; ///< number of bits used in shift register
/** Return mask for the state register */
uint64_t mask() const { return (mLen==64)?0xFFFFFFFFFFFFFFFFUL:((1<<mLen)-1); }
};
/**
A standard 9-bit based pseudorandom binary sequence (PRBS) generator.
Polynomial: x^9 + x^5 + 1
*/
class PRBS9 : public PRBS {
public:
PRBS9(uint64_t wState = 0x01)
: PRBS(9, 0x0110, wState)
{}
};
/**
A standard 15-bit based pseudorandom binary sequence (PRBS) generator.
Polynomial: x^15 + x^14 + 1
*/
class PRBS15 : public PRBS {
public:
PRBS15(uint64_t wState = 0x01)
: PRBS(15, 0x6000, wState)
{}
};
/**
A standard 64-bit based pseudorandom binary sequence (PRBS) generator.
Polynomial: x^64 + x^63 + x^61 + x^60 + 1
*/
class PRBS64 : public PRBS {
public:
PRBS64(uint64_t wState = 0x01)
: PRBS(64, 0xD800000000000000ULL, wState)
{}
};
#endif // PRBS_H