[Discuss-gnuradio] USRP FPGA 8-bit Data Ordering

[Paul Creekmore]

Context: I'm adding new quantization (sample width) options to the USRP FPGA configuration.  (Long time in coming; yes, I know.)

Question: I'm seeing that in 8-bit mode, the USRP outputs samples from its internal channels in the following sequence (an 8-bit, 8-channel example):

    1, 0,     3, 2,     5, 4,     7, 6,    1,0,   3,2,     ...

where each grouping of two channels makes one 16-bit word.

----> What is the rationale behind this convention? 

As I'm deciding how to output 4, 2, and 1-bit samples, it makes much more sense to me to use a sequential order, like this (4-bit, 8-channel example):

    0, 1, 2, 3,   4, 5, 6, 7,    0, 1, 2, 3,   ...

This way if the user writes the data directly to a file, one word after another, everything is in sequential order for whatever post-processing later.

----> Will the GNU Radio world fall apart if use a sequential channel ordering for my output and submit this development for inclusion in a future release?


Thanks,
Paul