[Discuss-gnuradio] trouble creating PMT uniform vectors in python that are the same type, but differ in value

[Collins, Richard]

Hello,

I just wanted to share some trouble I had trying to create a pmt uniform c32 vector in python, what I found as the fix, and hope to get some insight as to why things are this way.

Here's an entry from my notes:

THIS CREATES A VECTOR, BUT NOT A UNIFORM OR C32 VECTOR:

testv = pmt.to_pmt([complex(1.0), complex(-1.0)]*50)

pmt.is_vector(testv)             # True

pmt.is_uniform_vector(testv)     # False

pmt.is_c32vector(testv)          # False

THIS FAILS:

testv1 = pmt.make_c32vector(100, [complex(1.0), complex(-1.0)]*50)

THIS SUCCEEDS, but is a PITA:

testv1 = pmt.make_c32vector(100, complex(-1.0))

for i in range(pmt.length(testv)):
    if i%2 == 0:
        pmt.c32vector_set(testv, i, complex(1.0))

THIS IS THE CORRECT WAY TO DO IT:

testv2 = pmt.init_c32vector(100, [complex(1.0), complex(-1.0)]*50)

(SEE: http://lists.gnu.org/archive/html/discuss-gnuradio/2013-04/msg00292.html )

So, it took me quite a while to figure this out. Why does pmt.to_pmt(<python list of complex numbers>) return a vector, but fails when tested under pmt.is_uniform_vector() or any pmt.is_XXXvector() (i.e. c32 for XXX)?

Anyway, I'll just use pmt.init_c32vector(). I'm trying to create a data payoad for a PDU to send from my custom block to a PDU to tagged stream block such that large packets of samples (tens-of-thousands-of-generated-samples) can be sent out with reliable timing. I first looked into controlling a USRP sink with asynchronous commands, but from what I read, that method has some variability on the order of microseconds (which is still awesome, but I think it might not work well enough). I'm probably going about this all wrong, but it's a learning process, so let me know if there's a glaringly obvious method that I'm overlooking. I first looked into eventstream, as described by the oshearesearch website, but I think that's a bit too far into the deep end for a beginner like myself so far.

- Richard