Thanks Josh
Here is what I found empirically to answer my questions. This may help others as there doesn’t seem to be any thorough code example to send and receive:
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You can send the entire buffer straight, but it seems smaller buffer get transmitted faster (eg a 275000 samples buffer seems to start being transmitted around 200µs later than a 10 times smaller buffer)
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The transmission indeed stops once the whole buffer is sent (there used to be a bug in a previous version that required you to send 0s but it’s been fixed). Also just after setting the TX (not even starting the TX stream I think), you’ll see lots of noise at the corresponding central frequency. That noise will decrease dramatically once you’re done sending your 1st signal. Maybe 0s should also be sent automatically?
- Concerning the timeouts, my test was wrong indeed as it was filling up the buffers too fast.
In an attempt to transmit as fast as possible after receiving a signal, I played with latency and bufferLength (see Streaming.cpp).
Setting the latency to 1 (meaning max throughput, high latency) or the buffer length to something too big seems to add some latency. Setting latency to 0 and/or the buffer length to something smaller for both RX and TX helps.
The SOAPY_SDR_HAS_TIME flag can be used with writeStream to send a signal in the future at a specific timestamp. That’s the best way to avoid latency, but of course you need to already know the signal to send. It’s also possible to add several messages to be sent at different times next to each other (I think previously there was a bug that made everything be sent at the same time).
@andrewback @Zack I’ve noticed something strange though: it seems that changing the sampling rate of the TX impacts the RX and vice versa, depending on which one is setup last. Is it not possible to use different sampling rates for RX and TX?
Eg if I setup RX and then TX to both use 55MS/s, and I receive blocks of 1360 samples, the timestamp between received blocks is 12,364 as expected. If I setup RX to use 55MS/s and then TX to use 5MS/s, while still receiving blocks of 1360, the timestamp between received blocks is now 136,000, corresponding to RX at 5MS/s. Is this because