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Alexander Chemeris Alexander.Chemeris at fairwaves.coHi Josh, On Tue, Apr 8, 2014 at 11:00 PM, Josh Blum <josh at joshknows.com> wrote: > Hey guys, > > Please CC whoever appropriate. > > I have been looking over the u2plus_core.v and u2plus_umtrx_v2.v files > with the intention of updating the vita rx/tx chains and dsp chains. I > noticed a few interesting things about the clocking and I just wanted to > confirm some of my assumptions, a few possible changes, and possibly > share some knowledge. > > 1) vita chain/dsp core > Inside the u2plus_core.v, there is a 13MHz clock (lms_clk) that is used > to clock the time core and the dsps. The vita chain is clocked at 104MHz > (dsp_clk). So for example, when the dsp strobes out 1 sample, does the > vita_rx_chain see 8 of the same sample? > > My immediate concern is updating the vita and dsp chains. So, I really > just need to understand the interaction between the dsp and the vita > chain since they are crossing this 104/13Mhz clock domain. > > 2) usrp3 style vita framing/deframing > Some time after umtrx was released, B200 came out. The FPGA architecture > in B200 was changed from the earlier models to address dealing with > these integrated frontend chips. Specifically, the ADC, DAC, DSP, and > framing can all run on the same clock domain at full sample rate. This > is accomplished because the vita framing happens on 64-bit wide bus to > deal with the overhead of VITA headers. I suspect this architecture > would be better fitting for the UmTRX. I think the B200 architecture is better for UmTRX, but I'll let Andrew and Sergey to decide, as they know the FPGA code much better. > 3) u2plus_umtrx_v2.v > It looks like the ADC and DAC IQ signals are clocked in/out on the > positive and negative edges of the 13MHz clock. This is accomplished > using a 26 MHz clock. So technically, this is another clock domain > crossing between the 13/26MHz for the ADC/DAC signals. So, you should be > able to accomplish the same effect in with just the 13MHz clock using > the ODDR2 and IDDR2 xilinx modules. > > 4) digital loopback options? > I was looking for a way to do a digital loopback inside the LMS. I wasnt > sure if it was possible. Basically, if I set some value on the DAC pins, > can I get the same value of the ADC pins? I saw registers for baseband > loopback, but I think thats all analog. The idea is to self-test the bus > timing by putting a test word into the IOs. Unfortunately, there is no digital loopback in the LMS. As you correctly note, the baseband loopback is actually analog. > --- > In any case, the most important issue is #1. I want to have a host build > and image that is fully functional with latest UHD, lets say next week. > And I would like to be able to first verify with your team that we > havent lost any functionality, before further changes like the timed > command core. Sounds OK to you? Ok with me. > Thanks, > -josh > > > > -- Regards, Alexander Chemeris. CEO, Fairwaves, Inc. / ООО УмРадио https://fairwaves.co