GMSK demodulation

Hi there,

I’m writing a simple block to do some GSM processing, which right now
just looks for FCCH in the signal. The graph is constructed as
follows: usrp->low pass filter->gmsk.demod->my_block. My block
inherits from gr_sync_block. The problem I run into is the following
assertion failing: “gr_buffer.h:125: unsigned int
gr_buffer::index_add(unsigned int, unsigned int): Assertion `s <
d_bufsize’ failed.” This happens shortly after I start the program. I
tried removing any processing by my block and just returning
noutput_items in the work() function, which didn’t help. I then
removed the demodulator from the graph to see if the assertion would
still fail and the program ran fine. Is the gmsk.demod block too slow?
What other reasons are there for this error?

Thank you.