[alsa-devel] floating point exception triggered by speaker-test on pc-speaker

Alexander E. Patrakov patrakov at gmail.com
Sun Nov 23 10:30:24 CET 2008


I have hit a strange bug. To reproduce:

1. Build snd-pcsp.ko.

2. alsamixer -c pcsp, set the base frequency to 37286 Hz

3. $ speaker-test -r 22050 -P 4 -D plughw:pcsp

speaker-test 1.0.18

Playback device is plughw:pcsp
Stream parameters are 22050Hz, S16_LE, 1 channels
Using 16 octaves of pink noise
Rate set to 22050Hz (requested 22050Hz)
Buffer size range from 37 to 38756
Period size range from 18 to 19379
Using max buffer size 38756
Periods = 4
was set period_size = 0
was set buffer_size = 38756
  0 - Front Left
Floating point exception

I.e., as you see, period size somehow became 0. While debugging this with printfs, I 
noticed that the interval for periods in snd_pcm_hw_param_set_near() starts with 4, 
but doesn't include it (i.e., is open).

Also, I found that snd_interval_refine_first() and snd_interval_refine_last(), when 
given an open interval, refine it to something like (n n+1). This is obviously 
wrong, as there are no integer points in this interval. Changing i->max++ and 
i->min-- there to adjust the value by 2 did eliminate the floating point exception, 
but replaced it with "Unable to set nperiods 4 for playback: Invalid argument". So 
there must be something else also wrong, but I can't pinpoint it and give you a 
ready-made patch :(

Alexander E. Patrakov

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