Hello everyone,
I am experencing some issues when switching the sample rate.
I have two synchronized USRP X310 with a total of 4 TwinRX. I am doing
timed commands to jump around in the spectrum with all receivers at the
same frequency (SIMO stuff).
I also need to switch sample rates in between. When I keep the sample
rate constant, everything works fine, but once I switch it between two
timed receptions, I get very strange errors. Like I get an end-of-frame
after just a part of the samples I requested.
It seems like it is not possible to time the sample rate switch command.
Here is a debug output of my code which makes it quite clear what happens:
(1) Changed sample rate from 1e+07 to 5e+07
(2) Requested 32768 Samples
(3) Requested 32768 Samples
(4) Requested 32768 Samples
(5) Changed sample rate from 5e+07 to 1e+07
(6) Reading 32768 Samples
(7) Got only 6553 of 32768 samples at EOF
Commands 1-5 are transmitted to the USRP right away using its command
buffer. Then my program starts reading the first requested 32768 but
gets only 6553, which is precisely 1/5th of the requested samples. I
guess this is because he switched sample rate to 1/5th right before
executing the first stream command. But the sample rate switch is also
timed and should be executed after the three stream commands.
I attached the part of the code which is responsible for sending the
timed commands to the USRPs. This runs basically in a while(1) in a
seperate thread, while there is a seconds thread receiving the data
blocks, which produced the lines 6-7 of above output.
Is this a bug or feature I don't get? Are set_rx_rate commands not timed
when using set_command_time? How can I solve this isse? I need very
precise timing and also fast switching between frequencies and sample rates.
Best regards,
Fabian
double freq;
if(!getNextCmdFrequency(freq))
{
firstTime = true;
return;
}
//qDebug()<<"Generating recv
for"<<currentCmdBlockListID<<"/"<<currentCmdSlotListID;
// Check if this is the first command and reset current round time for
minimum time contraint
if(currentCmdBlockListID == 0 && currentCmdSlotListID == 0 &&
currentRoundTime < minimumRoundTime)
{
stream_cmd.time_spec += uhd::time_spec_t(minimumRoundTime -
currentRoundTime);
currentRoundTime = uhd::time_spec_t(0.0);
}
usrpDevice->set_command_time(stream_cmd.time_spec);
if(currentSampleRate != receiveBlockList[currentCmdBlockListID]->sampleRate)
{
double oldSampleRate = currentSampleRate;
currentSampleRate = receiveBlockList[currentCmdBlockListID]->sampleRate;
deviceConfig.sampleRate = currentSampleRate;
usrpDevice->set_rx_rate(currentSampleRate);
double newSampleRate = usrpDevice->get_rx_rate();
qDebug()<<"Changed sample rate
from"<<oldSampleRate<<"to"<<newSampleRate;
}
setFrequency(freq);
usrpDevice->clear_command_time();
// Stream command
stream_cmd.time_spec += receive_start_offset_ts; // delay by start offset
for the LO to lock
stream_cmd.num_samps =
receiveBlockList[currentCmdBlockListID]->samplesPerSlot;
ReceiveCmdTime receivecmdTime;
receivecmdTime.blockId = currentCmdBlockListID;
receivecmdTime.slotId = currentCmdSlotListID;
receivecmdTime.time = stream_cmd.time_spec.get_real_secs();
commandTimeMutex.lock();
commandTimeList.append(receivecmdTime);
commandTimeMutex.unlock();
rxStream->issue_stream_cmd(stream_cmd);
// Calcluate time for next slot
stream_cmd.time_spec +=
receiveBlockList[currentCmdBlockListID]->receiveTime + receive_stop_offset_ts;
currentRoundTime += receive_start_offset_ts +
receiveBlockList[currentCmdBlockListID]->receiveTime + receive_stop_offset_ts;_______________________________________________
USRP-users mailing list
USRP-users@lists.ettus.com
http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
