I see from the GNU Radio blocks that some of the Lime SDRs don’t support independent TX and RX sample rates.
From the GRC file: Note: LimeSDR-Mini and LimeSDR-Micro supports only the same sample rate for TX and RX. I can’t find any info on whether the XTRX supports this or not.
Does the XTRX support independent sample rates for the TX and RX?
The answer is yes and no… There is only one clock for the LMS7002 (CGEN module), but there are separate dividers for the receive and transmit channels. So, although they are not independent, you can change the ratio between them. I don’t use GNU Radio so I don’t know if they put the limitation on it. LimeSuite does give you visibility to these independent clock dividers.
Thanks for answering me. What are the parameters for the ratio? Is it something like power of 2 differences?
being a divider, it is a power of 2. Download LMS7002M-Programming-and-Calibration-Guide-v31r05.pdf and review the control diagram on page 88 (A2.8 CGEN Control Diagram)
The LMS7002M chip can have different sampling rates for Tx and Rx, but they are based on the same clock source as @Evan mentioned, so the possible difference between them would be limited by clock dividers.
In terms of board (like XTRX), the FPGA gateware expects that Rx and Tx sampling rates would be equal, as FPGA is using common timestamp counter for Rx and Tx transmission synchronization.
I’m trying to make sure I understand. It sounds like the LMS7002M chip supports different rates (via the divider), but the current gateware does not support it. Is that correct?
Yes, if I remember correctly, the gateware also has two separate PLL clocks for Rx and Tx, so I suppose it could support different rates, but as it is currently the gateware was not intended to be used with different rates.