[Discuss-gnuradio] usrp_sink_s and other quick questions

[Steven Clark]

Hi all-

Several quick questions.
1) For usrp sink_s, which bit of the short activates the MSB of the DAC chip? I.e., if I send 0bABCDEFGH IJKLMNOP, where each letter is either a 1 or a 0, which letter matches the MSB?

2) If I want to generate a stream of alternating zeros and ones (stored in bytes is fine): 0b00000000, 0b00000001, 0b00000000, 0b00000001, etc., which block is appropriate? ...now that I think about it, vector_source_b seems appropriate. I could loop the vector_source_b ([0b00000000, 0b00000001]), or I could loop vector_source_b ([0b01010101]) and send it to an unpacked_to_packed_bb(8). Is one of these ways preferred / less computationally intensive?

3) Interpolating. Let's talk first for a stream of floats: A, B, C, etc., coming out at rate x. If I just want to get A, A, B, B, C, C, coming out at rate 2x, is the best/only route to use gr_interp_fir_filter_fff with [1,1] as taps? Seems like there are some wasteful multiplies going on here. What about if I want to do this with a stream of bytes? There's no equivalent "gr_interp_fir_filter_bbb". Do I have to convert the bytes to float, then interp, then back to bytes?

Hopefully someone can help me out with some/all of these questions.
Thanks for your time.

-Steven