# Modifying dualRXTX.cpp example - sort of fixed now

**URL:** <https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844>\
**Category:** Lime Suite\
**Created:** [28 February 2017 17:02 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844 "2017-02-28T17:02:48Z")\
**Posts on this page:** 14\
**Page:** 1

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**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [28 February 2017 17:02 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/1 "2017-02-28T17:02:49Z")

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I am trying to modify the dualRXTX example that comes with LimSuite, basically I am using the original code  
by rather than echoing back the received samples I am transmitting my own samples instead. Trouble is I can’t  
get it to work.

The Lime tunes to the right frequency and when I call LMS\_SendStream it returns the number of samples  
I gave it. But nothing is visible on my spectrum analyser. Well that is not quite true, I can see the centre  
carrier leakage but no modulation.

I was expecting SendStream to block when the FIFO is full when timeout is set to zero but all it does is  
return 0 samples sent immediately.

It seems like everything is working except the DAC is not being updated. Anyone got any suggestions?

- Charles

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**Author:** ![jocover](https://avatars.discourse-cdn.com/v4/letter/j/e9bcb4/32.png) [@jocover](https://discourse.myriadrf.org/u/jocover)\
**Post date:** [28 February 2017 20:54 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/2 "2017-02-28T20:54:25Z")

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add enable tx antennal code  
if (LMS\_SetAntenna(device, LMS\_CH\_TX, 0, 1) != 0)  
error();

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**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [28 February 2017 21:34 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/3 "2017-02-28T21:34:53Z")

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I am afraid that didn’t make a difference.  
I did notice that setting timeout to 0 sets the timeout to 0 and does not do what it says in the header file  
which is sets timeout to infinity.

I have checked the values I am sending to the device which are valid. GetStreamStatus is reporting  
sensible information and no LMS calls are returning any error codes.

It is as if the first sample in a block goes to the DAC but nothing further. I am sending a complex  
signal that should output a tone 1 MHz from the carrier frequency.

- Charles

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**Author:** ![Zack](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/zack/32/89_2.png) [@Zack](https://discourse.myriadrf.org/u/Zack)\
**Post date:** [1 March 2017 10:11 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/4 "2017-03-01T10:11:46Z")

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Hi @g4guo,

Is the unmodified example working OK? Or you just get into the issue after code is modified? If yes, could you share the code please.

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**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [1 March 2017 11:22 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/5 "2017-03-01T11:22:04Z")

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Hi Zack,

The example appears to work so it is obviously something I am doing that is wrong.  
I have the added complexity of the fact I am compiling my code with NVIDIAs nvcc  
as I am working on a program that uses CUDA and GPUs to do the signal processing.

I recompiled the limesuite example using nvcc and it performs in the same way as the gcc  
version does. I will have a further look at what I am doing before I post the code.

I also currently have the Lime Calls in a thread so I need to check that is not the problem.

- Charles

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<div class="post-metadata">

**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [1 March 2017 16:07 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/6 "2017-03-01T16:07:31Z")

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Seems like the problem is down to flow control of the LMS\_SendStream.  
The example relies on using RecvStream and timestamps to flow control  
the Sending. If the Send queue overflows it breaks it.

The sampleRate field in the status message always returns 0 on both Tx and Rx.

So I am going to have to re-design my code to flow control the transmitter.

Shame there is no transmit only example. I suspect that is for the reason  
I have just encountered.

- Charles

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<div class="post-metadata">

**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [1 March 2017 21:20 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/7 "2017-03-01T21:20:00Z")

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What is happening is the tx stream fifo is filling up.  
The rx stream seems all right. Both tx and rx stream  
are configured as per the example code.

I have hacked together a standalone program that  
should output a 3 MHz sinewave on a 1GHz carrier.

Here is the dropbox link

> **[Dropbox - Link not found](https://www.dropbox.com/s/lltgtey1cfow2oi/mylime.cpp?dl=0)**
>
> Dropbox is a free service that lets you bring your photos, docs, and videos anywhere and share them easily. Never email yourself a file again!

- Charles

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<div class="post-metadata">

**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [2 March 2017 21:04 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/8 "2017-03-02T21:04:24Z")

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Seems I have fixed it.

Only LMS\_StartStream the streams you are going to use!  
If you start 2 streams but only use one of them it doesn’t like it.

I am still getting overruns on tx but that is due to me not understanding how  
the transmit flow control works.

- Charles

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**Author:** ![andrewback](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@andrewback](https://discourse.myriadrf.org/u/andrewback)\
**Post date:** [3 March 2017 08:55 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/9 "2017-03-03T08:55:11Z")

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Great to hear you are making progress, Charles! Keep us posted and let us know if there is anything we can help with.

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<div class="post-metadata">

**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [3 March 2017 10:29 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/10 "2017-03-03T10:29:26Z")

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Hi Andrew,  
Yes I am getting somewhere. My application will require the USB3 interface to  
operate at it’s maximum.

I have found that setting timeout to 0 in LMS\_SendStream is not a good idea.  
The header file seems to indicate that should set the timeout to infinity. It seems  
better to set it to a large value instead, setting it to zero’s increases signal dropouts.

I have also found that to get maximum throughput it is essential to set the channel  
to 1.0 in the latencyVsThrougput field.

I have tried increasing the value of the fifoSize field in the stream configuration but  
whatever value I set it to GetStreamStatus always reports a fifoSize of 8192.

I think to get the maximum possible throughput I need a much larger fifo (I am not worried about  
latency).

Basically I would like to run the board flat out in full duplex on a single channel.

- Charles

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<div class="post-metadata">

**Author:** ![IgnasJ](https://avatars.discourse-cdn.com/v4/letter/i/278dde/32.png) [@IgnasJ](https://discourse.myriadrf.org/u/IgnasJ)\
**Post date:** [3 March 2017 11:00 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/11 "2017-03-03T11:00:56Z")

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Hi,  
Looking at the fifo code I can see that there might be a bug that ignores timeout and overwrites the oldest data immediately when fifo is full and synchronization to timestamps is enabled.  
You can try disabling synchronization to timestamps by setting:  
tx\_metadata.waitForTimestamp = false;

Also, you are right about incorrect description of timeout=0 in the header file.When fifo is full it doesn’t block at all and return with 0 samples written. Use reasonably high timeout value for blocking instead.

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<div class="post-metadata">

**Author:** ![jocover](https://avatars.discourse-cdn.com/v4/letter/j/e9bcb4/32.png) [@jocover](https://discourse.myriadrf.org/u/jocover)\
**Post date:** [3 March 2017 11:03 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/12 "2017-03-03T11:03:32Z")

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I think this’s a bug ,bufferLength value is always 65536

[https://github.com/myriadrf/LimeSuite/blob/master/src/API/lms7\_api.cpp#L1582](https://github.com/myriadrf/LimeSuite/blob/master/src/API/lms7_api.cpp#L1582)

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<div class="post-metadata">

**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [3 March 2017 11:16 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/13 "2017-03-03T11:16:03Z")

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Interesting.

The number of samples it reports is 8192 as I am using 16 bit samples each complex sample would require 4 bytes.  
4 \* 8192 = 3276.

I wonder if the 65536 is a physical limitation?

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<div class="post-metadata">

**Author:** ![g4guo](https://yyz2.discourse-cdn.com/flex034/user_avatar/discourse.myriadrf.org/g4guo/32/146_2.png) [@g4guo](https://discourse.myriadrf.org/u/g4guo)\
**Post date:** [3 March 2017 11:17 UTC](https://discourse.myriadrf.org/t/modifying-dualrxtx-cpp-example-sort-of-fixed-now/844/14 "2017-03-03T11:17:39Z")

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Being lazy I hadn’t got around to “feeling the source” but that seems to confirm what I have been seeing.