This page describes the build-in ALSA driver tool to debug PCM ring buffer positions.
Replace '#' with your card number (usually 0). This proc file can enable various debugging tools. The CONFIG_SND_PCM_XRUN_DEBUG, CONFIG_SND_VERBOSE_PROCFS, CONFIG_SND_DEBUG options must be enabled in your kernel (if xrun_debug proc file is present - this feature is enabled).
1 Basic debugging - show xruns in ksyslog interface 2 Dump stack - dump stack for basic debugging 4 Jiffies check - compare the position with kernel jiffies (a sort of in-kernel monotonic clock), show what's changed when basic debugging is enabled 8 Dump positions on each period update call 16 Dump positions on each hardware pointer update call 32 Enable logging of last 10 ring buffer positions 64 Show the last 10 ring buffer position only once (when first error situation occured)
To enable more features just do sum values of above (for example 1+2=3).
Some good value combinations:
# Enable basic debugging and dump stack # Usefull to just see, if PCM stream is stopped for a reason (usually wrong audio process timing from scheduler) echo 3 > /proc/asound/card0/pcm0p/xrun_debug
# Enable basic debugging, do jiffies check and enable one shot dump of last 10 ring buffer positions # Usefull, when the position is broken only after some of time (to reduce ksyslog messages) echo 101 > /proc/asound/card0/pcm0p/xrun_debug
# Enable basic debugging, do jiffies check and dump position on each period and hardware pointer update calls # Usefull when the lowlevel (specific) hardware driver is somehow broken echo 29 > /proc/asound/card0/pcm0p/xrun_debug