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Re: [Discuss-gnuradio] seg fault in volk_32f_s32f_multiply_32f_a_sse gnu

From: ikjtel
Subject: Re: [Discuss-gnuradio] seg fault in volk_32f_s32f_multiply_32f_a_sse gnuradio v 3.6.1
Date: Tue, 4 Sep 2012 18:01:17 -0700 (PDT)

> Yes, looks like it. But it's an Atom, which might change things. I

> know we had some issues on Atom's before, but I thought that we worked
> them out. I'll be interested to see how cmake reports the architecture
> checks for VOLK here.

Hi Tom

I've made some further progress, and this may be premature, but I'll go so far 
as to say we can rule this out entirely.

Here's a strawman theory - criticism of the theory is invited, shooting it down 
would be welcomed ; )

Our app uses lots of disconnect() and connect() calls because our appetite for 
widgets is bigger than the CPU available.  Also, since the widgets are 
tab-selectable there is only one widget visible at a time.  So when the user 
hits a tab we call disconnect and connect (surrounded by lock() / unlock() of 
course) in order to dynamically create a flow graph that connects up all the 
elements needed by that tab (and disconnects the elements, filters, demods, 
FFT's and other blocks that aren't needed by this tab, to conserve CPU.

The theory is that this is "messing up" the boundary alignments of the operands 
to the SSE instructions, making them no longer properly aligned, resulting in a 

Here's the minimal python app , it seg faults in volk 100% reliably for me.  If 
the call to shuffle() is removed, the script does not crash.


p.s. kindly let me know if this code isn't properly machine-readable
#!/usr/bin/env python
import math
import time
from gnuradio import gr, gru, audio, eng_notation, blks2, optfir

class app_top_block(gr.top_block):
    def __init__(self):
        gr.top_block.__init__(self, "mhp")

        self.source = gr.sig_source_f(48000, gr.GR_TRI_WAVE, 1.0, 1.0, 0)
        self.amp = gr.multiply_const_ff(65.0)
        self.sink = gr.null_sink(gr.sizeof_float)
        self.connect(self.source, self.amp, self.sink)
        self.amp_connected = True

    def shuffle(self):
        if self.amp_connected:
            self.disconnect(self.source, self.amp, self.sink)
            self.connect(self.source, self.sink)
            self.disconnect(self.source, self.sink)
            self.connect(self.source, self.amp, self.sink)
        self.amp_connected = not self.amp_connected

if __name__ == "__main__":
    tb = app_top_block()
    while True:

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