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Get around the viterbi kernel issue in Volk
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Aang23
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3 changed files with 207 additions and 12 deletions
11
README.md
11
README.md
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@ -4,17 +4,6 @@ A generic satellite data processing software.
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**Still WIP**
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# Important - Possible issues with VOLK Viterbi decoding (Windows users can probably ignore this)
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/!\ Some decoders utilize VOLK's Viterbi decoder. But as of writing this, only the "spiral" (SSE) implementation performs as intended. Please ensure you have it set as such in your volk_config or things may not work as expected! /!\
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On Windows, this should not be necessary as it this will (should!) be the default already.
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On Linux, Mac OS and similar platforms, please edit your ~/.volk/volk_config file.
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Find the line referring to `volk_8u_x4_conv_k7_r2_8u`, and make sure it contains the following : `volk_8u_x4_conv_k7_r2_8u spiral spiral`.
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If you are using an ARM-based machine (Raspbery Pi, most Android devices), there is unfortunately no way around poorer decoding performances of the "generic" kernel... Until this gets fixed in VOLK itself.
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# Usage
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First of all, as with any program using volk, running volk_profile once is highly recommended for better performances.
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@ -15,6 +15,8 @@
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#include <cstdio>
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#include <sstream>
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#include <vector>
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#include "logger.h"
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#include "volk_k7_r2_generic_fixed.h"
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namespace fec
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{
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@ -122,7 +124,35 @@ namespace fec
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d_SUBSHIFT = 0;
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}
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std::map<std::string, conv_kernel> yp_kernel = {{"k=7r=2", volk_8u_x4_conv_k7_r2_8u}};
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conv_kernel k7_r2_kernel = volk_fixed::volk_8u_x4_conv_k7_r2_8u_generic; // Default to our fixed generic kernel
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// We need to get around Volk's broken generic and AVX kernel....
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{
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volk_func_desc k7_r2_desc = volk_8u_x4_conv_k7_r2_8u_get_func_desc(); // Check what kernels are available
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bool has_spiral = false;
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for (int i = 0; i < (int)k7_r2_desc.n_impls; i++)
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{
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if (std::string(k7_r2_desc.impl_names[i]) == "spiral") // Try to find spiral
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{
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has_spiral = true;
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break;
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}
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}
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if (has_spiral)
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{ // If spiral is available, use it
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logger->trace("Volk has the spiral kernel using it!");
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k7_r2_kernel = volk_fixed::volk_8u_x4_conv_k7_r2_8u_spiral;
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}
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else
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{ // Stick to our fixed kernel
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logger->trace("Volk does not have the spiral kernel, will default to bundled generic.");
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}
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}
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std::map<std::string, conv_kernel> yp_kernel = {{"k=7r=2", k7_r2_kernel}};
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std::string k_ = "k=";
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std::string r_ = "r=";
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176
src-core/common/codings/viterbi/volk_k7_r2_generic_fixed.h
Normal file
176
src-core/common/codings/viterbi/volk_k7_r2_generic_fixed.h
Normal file
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@ -0,0 +1,176 @@
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/* -*- c++ -*- */
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/*
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* Copyright 2014 Free Software Foundation, Inc.
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*
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* This file is part of GNU Radio
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*
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* GNU Radio is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* GNU Radio is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with GNU Radio; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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/*!
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* \page volk_8u_x4_conv_k7_r2_8u
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*
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* \b Overview
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*
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* Performs convolutional decoding for a K=7, rate 1/2 convolutional
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* code. The polynomials user defined.
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*
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* <b>Dispatcher Prototype</b>
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* \code
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* void volk_8u_x4_conv_k7_r2_8u(unsigned char* Y, unsigned char* X, unsigned char* syms,
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* unsigned char* dec, unsigned int framebits, unsigned int excess, unsigned char*
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* Branchtab) \endcode
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*
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* \b Inputs
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* \li X: <FIXME>
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* \li syms: <FIXME>
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* \li dec: <FIXME>
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* \li framebits: size of the frame to decode in bits.
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* \li excess: <FIXME>
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* \li Branchtab: <FIXME>
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*
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* \b Outputs
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* \li Y: The decoded output bits.
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*
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* \b Example
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* \code
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* int N = 10000;
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*
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* volk_8u_x4_conv_k7_r2_8u();
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*
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* volk_free(x);
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* \endcode
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*/
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// The default version in Volk is broken right now, so I am including this fix
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// SatDump will default to unless volk_config returned a working implemenation
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#ifndef INCLUDED_volk_8u_x4_conv_k7_r2_8u_H
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#define INCLUDED_volk_8u_x4_conv_k7_r2_8u_H
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#include <volk/volk.h>
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namespace volk_fixed
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{
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typedef union
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{
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unsigned char /*DECISIONTYPE*/ t[64 /*NUMSTATES*/ / 8 /*DECISIONTYPE_BITSIZE*/];
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unsigned int w[64 /*NUMSTATES*/ / 32];
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unsigned short s[64 /*NUMSTATES*/ / 16];
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unsigned char c[64 /*NUMSTATES*/ / 8];
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#ifdef _MSC_VER
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} decision_t;
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#else
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} decision_t __attribute__((aligned(16)));
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#endif
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static inline void renormalize(unsigned char *X, unsigned char /*threshold*/)
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{
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int NUMSTATES = 64;
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int i;
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unsigned char min = X[0];
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// if(min > threshold) {
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for (i = 0; i < NUMSTATES; i++)
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if (min > X[i])
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min = X[i];
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for (i = 0; i < NUMSTATES; i++)
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X[i] -= min;
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//}
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}
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// helper BFLY for GENERIC version
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static inline void BFLY(int i,
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int s,
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unsigned char *syms,
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unsigned char *Y,
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unsigned char *X,
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decision_t *d,
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unsigned char *Branchtab)
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{
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int j, decision0, decision1;
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unsigned char metric, m0, m1, m2, m3;
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int NUMSTATES = 64;
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int RATE = 2;
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int METRICSHIFT = 2;
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int PRECISIONSHIFT = 2;
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metric = 0;
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for (j = 0; j < RATE; j++)
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metric += (Branchtab[i + j * NUMSTATES / 2] ^ syms[s * RATE + j]) >> METRICSHIFT;
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metric = metric >> PRECISIONSHIFT;
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unsigned char max = ((RATE * ((256 - 1) >> METRICSHIFT)) >> PRECISIONSHIFT);
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m0 = X[i] + metric;
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m1 = X[i + NUMSTATES / 2] + (max - metric);
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m2 = X[i] + (max - metric);
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m3 = X[i + NUMSTATES / 2] + metric;
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decision0 = (signed int)(m0 - m1) > 0;
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decision1 = (signed int)(m2 - m3) > 0;
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Y[2 * i] = decision0 ? m1 : m0;
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Y[2 * i + 1] = decision1 ? m3 : m2;
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d->w[i / (sizeof(unsigned int) * 8 / 2) +
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s * (sizeof(decision_t) / sizeof(unsigned int))] |=
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(decision0 | decision1 << 1) << ((2 * i) & (sizeof(unsigned int) * 8 - 1));
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}
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static inline void volk_8u_x4_conv_k7_r2_8u_generic(unsigned char *Y,
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unsigned char *X,
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unsigned char *syms,
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unsigned char *dec,
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unsigned int framebits,
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unsigned int excess,
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unsigned char *Branchtab)
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{
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int nbits = framebits + excess;
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int NUMSTATES = 64;
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int RENORMALIZE_THRESHOLD = 210;
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int s, i;
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for (s = 0; s < nbits; s++)
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{
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void *tmp;
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for (i = 0; i < NUMSTATES / 2; i++)
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{
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BFLY(i, s, syms, Y, X, (decision_t *)dec, Branchtab);
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}
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renormalize(Y, RENORMALIZE_THRESHOLD);
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/// Swap pointers to old and new metrics
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tmp = (void *)X;
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X = Y;
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Y = (unsigned char *)tmp;
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}
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}
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static inline void volk_8u_x4_conv_k7_r2_8u_spiral(unsigned char *Y,
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unsigned char *X,
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unsigned char *syms,
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unsigned char *dec,
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unsigned int framebits,
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unsigned int excess,
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unsigned char *Branchtab)
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{
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volk_8u_x4_conv_k7_r2_8u_manual(Y, X, syms, dec, framebits, excess, Branchtab, "spiral");
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}
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};
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#endif /*INCLUDED_volk_8u_x4_conv_k7_r2_8u_H*/
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