----------------------------- Included message --------------- Message: 5 Date: Tue, 27 Oct 2020 20:28:12 -0400 From: "Marcus D. Leech" <patchvonbr...@gmail.com> To: usrp-users@lists.ettus.com Subject: Re: [USRP-users] USRP B200mini half-duplex 1 port Message-ID: <5f98bb1c.7070...@gmail.com> Content-Type: text/plain; charset=windows-1252; format=flowed
On 10/27/2020 08:24 PM, Alvaro Pendas Recondo via USRP-users wrote: > Hello, > > I am trying to implement a half-duplex system with one antenna, > preferably using just one port in the USRP device. I have noticed that > the port that is labelled as TX in the B200mini can also receive (the > same as the TX/RX port in the "normal" B200). My question is, is it > possible to change modes in that port during execution time? I have > read that, as a rule of thumb, the port should receive as default and > transmit when it receives samples to do so. However, I do not know if > that functionality applies to the B200mini. > > If it is possible, do you have any general ideal about the best way to > do it in GNURadio? > > Best regards, > > Alvaro > > As far as I know the TX port on the B200mini is actually a TX/RX port, and the transmit/receive switching logic is implemented in the hardware. You might post to the discuss-gnuradio mailing list on topics related to Gnu Radio. I've never implemented a TX/RX application in GR myself, but I'm fairly sure the hardware supports it. --------------------------------------------------------------- Assuming you are using the B205mini - the TX/RX port switching appears to work on detecting samples in the transmit buffer (FIFO). When the Tx FIFO is empty it switches to receive. There are a number of problems with this, in that once in receive it is very difficult to fill the transmit FIFO enough to get it to transmit continuously again. What happens is that if the transmit source is throttled in any manner, a few samples get TX queued then the mini switches to TX and empties the FIFO enough to switch back to receive. So it goes into a high-speed Tx/Rx/Tx/Rx/Tx/Rx ..... mode. Using for example an audio source causes sample rate limiting to the rate of that source. If instead a source is provided that can burst a whole bunch of samples to the TX Fifo, then it gets into TX mode and stays. For example, a constant source with no throttling. Unfortunately this isn't so useful for actual information. All the above tested at a sample rates of 96 ksps and some lower. Higher sample rates have not been tried, probably the behavior would be different. Finding any documentation about what is going on, how it works, FIFO sizes, %FULL %EMPTY trigger levels, etc. has been fruitless so far. -- Tom, N5EG
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