I think that there's a weird corner-case with offsets of 0 whereby it shows up a clock early in the downsampling (because 0 offset falls right on the downsample boundary). That's why there's a special delay for the 0-offset case.
Of course, you know this is just a simulation-level part of the block. It does not get mapped into hardware at all--it's just to give some basic simulation functionality to the block. So if the output looks like what you expect, the details of the simulation model aren't terribly important. On Fri, Feb 19, 2010 at 10:04 AM, Jonathan Landon < silicondiode2...@yahoo.com> wrote: > Inside the adc block with interleave mode on, the decimate-by-8 downsample > blocks have offsets of 1,3,5,7 on channels i0-i3, and offsets of 0,2,4,6 on > channels q0-q3, for 800MHz sampling, and sample time = 0.25. This all seems > reasonable, but the delays seem inconsistent -- for the i-channels the > delays are all 1, but for the q-channels the first is 2 and the rest are 1. > When I uncheck the "ADC interleave mode" box, the downsample blocks change > to decimate by 4, and the i- and q-channel delays are both set with the > first at 2 and the rest 1. These delays seem strange to me -- I expect them > to all be the same and have the downsample blocks take care of the delays, > or have successively longer delays while keeping the downsample blocks the > same. So having one delay set at 2 and the rest at 1 seems strange, and > having the i-channels and q-channels behave differently for interleave-mode > on vs. off seems strange. When interleave mode is turned off, the > downsample blocks are running the function sdspdsamp2, but since they're all > running the same version of that function, shouldn't the delays be set as > 1,2,3,4, instead of 2,1,1,1? > > I didn't find an explanation for this in the CASPER memos, and Jason says > he didn't exped the adc block to be set up like this. Does anyone else know > why the delays are set up like this? (I'm using the 10.1 tools on > otto.eecs.berkeley.edu, in case it helps) > > Thanks, > Jonathan Landon > > > -- Aaron Parsons 510-406-4322 (cell) Campbell Hall 523, UCB
