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Ensure IQ buffer size is a power of two, as required by decimators

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This commit is contained in:
Jon Beniston 2022-02-24 16:27:32 +00:00
parent 113aff6e57
commit ffe96cbf63
2 changed files with 47 additions and 1 deletions
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6
plugins/samplesource/usrpinput/usrpinput.cpp
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@ -35,6 +35,7 @@
#include "device/deviceapi.h"
#include "dsp/dspcommands.h"
#include "dsp/dspengine.h"
#include "util/poweroftwo.h"
#include "usrpinput.h"
#include "usrpinputthread.h"
#include "usrp/deviceusrpparam.h"
@ -338,8 +339,11 @@ bool USRPInput::acquireChannel()
m_streamId = m_deviceShared.m_deviceParams->getDevice()->get_rx_stream(stream_args);
// Match our receive buffer size to what UHD uses
// Decimators require buffers to sized as powers of two (See #1161)
m_bufSamples = m_streamId->get_max_num_samps();
if (!isPowerOfTwo(m_bufSamples)) {
m_bufSamples = lowerPowerOfTwo(m_bufSamples);
}
// Wait for reference and LO to lock
DeviceUSRP::waitForLock(usrp, m_settings.m_clockSource, m_deviceShared.m_channel);

42
sdrbase/util/poweroftwo.h Normal file
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@ -0,0 +1,42 @@
///////////////////////////////////////////////////////////////////////////////////
// Copyright (C) 2022 Jon Beniston, M7RCE //
// //
// This program is free software; you can redistribute it and/or modify //
// it under the terms of the GNU General Public License as published by //
// the Free Software Foundation as version 3 of the License, or //
// (at your option) any later version. //
// //
// This program 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 General Public License V3 for more details. //
// //
// You should have received a copy of the GNU General Public License //
// along with this program. If not, see <http://www.gnu.org/licenses/>. //
///////////////////////////////////////////////////////////////////////////////////
#ifndef INCLUDE_POWEROFTWO_H
#define INCLUDE_POWEROFTWO_H
#include <cstdint>
// Is x a power of two
// From: https://stackoverflow.com/questions/600293/how-to-check-if-a-number-is-a-power-of-2
static bool isPowerOfTwo(uint32_t x)
{
return (x & (x - 1)) == 0;
}
// Calculate next power of 2 lower than x
// From: https://stackoverflow.com/questions/2679815/previous-power-of-2
static uint32_t lowerPowerOfTwo(uint32_t x)
{
x = x | (x >> 1);
x = x | (x >> 2);
x = x | (x >> 4);
x = x | (x >> 8);
x = x | (x >> 16);
return x - (x >> 1);
}
#endif /* INCLUDE_POWEROFTWO_H */