On Wed, Jan 21, 2009 at 05:47:19PM -0500, Paul Creekmore wrote: > Paul Creekmore wrote: >> 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 > Amendment: > > I see now why the sequence is as it is. As a real-time program reads > one word at a time and picks off samples from LSB to MSB, the ordering > makes sense. I may just include a setting to reverse the sample order > for more efficient data recording. If the powers that be have any other > thoughts, please let me know. > > --Paul
Thanks for answering your own question :-) The USRP1 is little endian. My not-fully-considered thought is that it ought to go like this (everything packed into a 32-bit word): 16 bit I & Q (same as today): +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Q0 | I0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8 bit I & Q (different from today: see usrp_source_c.cc): +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Q1 | I1 | Q0 | I0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4 bit I & Q: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Q3 | I3 | Q2 | I2 | Q1 | I1 | Q0 | I0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ etc... What are you thoughts about this? Eric _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
