Re: [Discuss-gnuradio] Input Selector

[Marcus Müller]

Hi Rich,

sounds like a job for gr-eventstream[1] to only put in info when some event occured (i.e. when a message was sent to the eventstream block), and maybe gr-msgtools to convert the change in variable value from a "QT GUI Pushbutton" to a message, and a self-written (might be simple enough to do in Python) block that has a message input and a message output and, upon change, sends a event-stream-event-compatible message to the event stream source, containing the contents of the file.  Then you'd write a mux and be done.

To be completely honest, though it's a bit like re-inventing gr-eventstream, I'd probably just use the aforementioned pushbutton, convert its pushbutton variable change to a message using gr-msgtools' Variable To Message block to convert that to a variable, and write a quick C++ or python block that has a "passthrough" stream input, a "interject" message input, and a stream output. Whenever there's a "pressed" message, it would disrupt its normal activity of passing through the input, and change into a state of inserting samples from a file, till the complete file is read completely. Sounds like not-so-much code.

Note that message handling happens asynchronous, ie. only *in between* calls to work. So, always consider that handling a message of this sorts has a worst-case latency of f_sample * size_of_output buffer + Python/Qt overhead. Luckily, you can restrict the output buffer size, or you could even intentionally never produce too many samples at once.

Best regards,

Marcus

[1] https://oshearesearch.com/index.php/2015/03/15/burst-transmission-in-gnu-radio-sample-streams-with-eventstream/

On 25.07.2016 20:28, Richard Bell wrote:

Hello,

I need to let the user select which input stream to transmit by pushing a button on the GUI. By default, the transmitter transmits random data until the user clicks the button, at which point a file is transmitted.

It is important that the entire file be transmitted, from the beginning. This means that the file data stream can't be dropped to the floor until the user clicks the button, it must apply back pressure from the selector block to the file source block until the user presses the button.

The selector block uses a null sink for each stream that isn't connected to the output, so I loose the ability to send the file from the beginning. In addition, the selector is causing the flowgraph to close with return code -11 and no other message.

Does someone have an idea of how I could do this using GRC?

Thank you,

Rich

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