I’ve been desparate lately for a way to stream data from GNURadio back
to the hardware world without turning the data into an analog signal via
USRP’s DAC. For example, if I have a software demodulator outputting
bit per byte, as done via a slicer in many of the examples), I would
get that bit stream out to a digital pin on a USRP daughtercard. This
enable things like automated bit error rate testing.
I think I have an idea for how to do this, but I need somebody to check
Let’s say I have an unused BasicTX daughtercard. The idea is to alter
FPGA’s .rbf file so that the MSB line going to the DAC is also connected
one of the io pins on the d’card. Now, some demod blocks (gmsk, for
output a stream of floats representing soft symbols that are then
thresholded (sliced) to produce a stream of bytes. Instead of slicing,
I convert my float stream to complex and send it to a usrp sink (the
TX), and thereby get my bits out on that io pin? The output of the DAC
be nonsensical, but I wouldn’t be using it anyway, so who cares?
Does this approach make sense? Is there an easier way to do this sort of
thing? Anything I need to be wary of (damaging my hardware, for
If there is no better way to do this, then Ettus should really make a
Digital I/O daughtercard – it would sell like hotcakes.