Re: [USRP-users] USRP B200mini half-duplex 1 port
On 10/28/2020 12:42 PM, Tom McDermott via USRP-users wrote: - Included message --- Message: 5 Date: Tue, 27 Oct 2020 20:28:12 -0400 From: "Marcus D. Leech" <mailto:patchvonbr...@gmail.com>> To: usrp-users@lists.ettus.com <mailto:usrp-users@lists.ettus.com> Subject: Re: [USRP-users] USRP B200mini half-duplex 1 port Message-ID: <5f98bb1c.7070...@gmail.com <mailto: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 My guess is that 96ksps is way too low a sample rate to keep the TX FIFO happy. If you're using an audio source, you probably need to re-sample up to a higher rate, and whenever you have two bits of hardware with their own sample clocks, you have the "two clock" problem. What is needed is an elastic buffer with notions (feedback) about how close the audio system is to over-running or under-running, and the DSP flow tweaks the sample rate ever-so-slightly as appropriate. This is why professional audio systems use samplers that are all mutually clock-locked to one another--otherwise, the "two clock" problem is inevitable. ___ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
Re: [USRP-users] USRP B200mini half-duplex 1 port
- Included message --- Message: 5 Date: Tue, 27 Oct 2020 20:28:12 -0400 From: "Marcus D. Leech" 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 ___ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
Re: [USRP-users] USRP B200mini half-duplex 1 port
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. ___ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
[USRP-users] USRP B200mini half-duplex 1 port
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 ___ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
