I am currently trying to debug a buffer overrun when capturing with the BeagleBone Black and Audio Cape attached on 3.13-rc8, this is pretty much the same setup as the am335x-evm. The following is the traceback captured using the XRUN_BUFFER_DEBUG kernel config option. I think an interrupt is taking too long to return.

Example Traceback 1 (Writing to uSD card)

[ 802.578728] ALSA sound/core/pcm_lib.c:177 XRUN: pcmC0D0c:0 CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.13.0-rc8-00005-ga6da83f-dirty #12 [ 802.593139] [<c00160e8>] (unwind_backtrace+0x0/0x12c) from [<c0012b08>] (show_stack+0x10/0x14) [ 802.602174] [<c0012b08>] (show_stack+0x10/0x14) from [<c058c80c>] (dump_stack+0x7c/0x94) [ 802.610659] [<c058c80c>] (dump_stack+0x7c/0x94) from [<c04862e8>] (xrun+0x80/0xb0) [ 802.618596] [<c04862e8>] (xrun+0x80/0xb0) from [<c0486e1c>] (snd_pcm_update_state+0xf8/0x100) [ 802.627531] [<c0486e1c>] (snd_pcm_update_state+0xf8/0x100) from [<c0487048>] (snd_pcm_update_hw_ptr0+0x224/0x82c) [ 802.638281] [<c0487048>] (snd_pcm_update_hw_ptr0+0x224/0x82c) from [<c0487700>] (snd_pcm_period_elapsed+0xb0/0xf4) [ 802.649131] [<c0487700>] (snd_pcm_period_elapsed+0xb0/0xf4) from [<c0021458>] (dma_irq_handler+0x130/0x1f4) [ 802.659345] [<c0021458>] (dma_irq_handler+0x130/0x1f4) from [<c008e504>] (handle_irq_event_percpu+0x5c/0x21c) [ 802.669735] [<c008e504>] (handle_irq_event_percpu+0x5c/0x21c) from [<c008e700>] (handle_irq_event+0x3c/0x5c) [ 802.680035] [<c008e700>] (handle_irq_event+0x3c/0x5c) from [<c0091038>] (handle_level_irq+0xac/0x118) [ 802.689697] [<c0091038>] (handle_level_irq+0xac/0x118) from [<c008dc8c>] (generic_handle_irq+0x28/0x3c) [ 802.699542] [<c008dc8c>] (generic_handle_irq+0x28/0x3c) from [<c000f968>] (handle_IRQ+0x4c/0xb4) [ 802.708750] [<c000f968>] (handle_IRQ+0x4c/0xb4) from [<c00085b4>] (omap3_intc_handle_irq+0x60/0x74) [ 802.718237] [<c00085b4>] (omap3_intc_handle_irq+0x60/0x74) from [<c0592a64>] (__irq_svc+0x44/0x5c) [ 802.727618] Exception stack(0xc088df58 to 0xc088dfa0) [ 802.732912] df40: 00000001 00000001 [ 802.741479] df60: 00000000 c0897cb0 c088c000 c088c000 00000000 c0933bd4 c08949a0 c0894880 [ 802.750047] df80: c0894930 c059f4a8 c088c020 c088dfa0 c0082ef8 c000fd00 20070013 ffffffff [ 802.758620] [<c0592a64>] (__irq_svc+0x44/0x5c) from [<c000fd00>] (arch_cpu_idle+0x20/0x3c) [ 802.767283] [<c000fd00>] (arch_cpu_idle+0x20/0x3c) from [<c008db84>] (cpu_startup_entry+0x120/0x1f0) [ 802.776858] [<c008db84>] (cpu_startup_entry+0x120/0x1f0) from [<c0826a9c>] (start_kernel+0x304/0x364)

Example Traceback 2 (Writing to tmpfs)

[ 1310.025256] ALSA sound/core/pcm_lib.c:177 XRUN: pcmC0D0c:0 [ 1310.031046] CPU: 0 PID: 998 Comm: avconv Not tainted 3.13.0-rc8-00005-ga6da83f-dirty #12 [ 1310.039580] [<c00160e8>] (unwind_backtrace+0x0/0x12c) from [<c0012b08>] (show_stack+0x10/0x14) [ 1310.048615] [<c0012b08>] (show_stack+0x10/0x14) from [<c058c80c>] (dump_stack+0x7c/0x94) [ 1310.057102] [<c058c80c>] (dump_stack+0x7c/0x94) from [<c04862e8>] (xrun+0x80/0xb0) 1310.065039] [<c04862e8>] (xrun+0x80/0xb0) from [<c0486e1c>] (snd_pcm_update_state+0xf8/0x100) [ 1310.073974] [<c0486e1c>] (snd_pcm_update_state+0xf8/0x100) from [<c0487048>] (snd_pcm_update_hw_ptr0+0x224/0x82c) [ 1310.084724] [<c0487048>] (snd_pcm_update_hw_ptr0+0x224/0x82c) from [<c0487700>] (snd_pcm_period_elapsed+0xb0/0xf4) [ 1310.095574] [<c0487700>] (snd_pcm_period_elapsed+0xb0/0xf4) from [<c0021458>] (dma_irq_handler+0x130/0x1f4) [ 1310.105788] [<c0021458>] (dma_irq_handler+0x130/0x1f4) from [<c008e504>] (handle_irq_event_percpu+0x5c/0x21c) [ 1310.116178] [<c008e504>] (handle_irq_event_percpu+0x5c/0x21c) from [<c008e700>] (handle_irq_event+0x3c/0x5c) [ 1310.126477] [<c008e700>] (handle_irq_event+0x3c/0x5c) from [<c0091038>] (handle_level_irq+0xac/0x118) [ 1310.136138] [<c0091038>] (handle_level_irq+0xac/0x118) from [<c008dc8c>] (generic_handle_irq+0x28/0x3c) [ 1310.145982] [<c008dc8c>] (generic_handle_irq+0x28/0x3c) from [<c000f968>] (handle_IRQ+0x4c/0xb4) [ 1310.155190] [<c000f968>] (handle_IRQ+0x4c/0xb4) from [<c00085b4>] (omap3_intc_handle_irq+0x60/0x74) [ 1310.164677] [<c00085b4>] (omap3_intc_handle_irq+0x60/0x74) from [<c0592a64>] (__irq_svc+0x44/0x5c) [ 1310.174056] Exception stack(0xde0f7ee0 to 0xde0f7f28) [ 1310.179354] 7ee0: 00000001 00000000 00000000 de3f8a80 00000000 00000002 c0047968 00000054 [ 1310.187920] 7f00: 00000000 b5440c64 c0933670 beb92fb8 de0f6028 de0f7f28 c0082eb0 c0047348 [ 1310.196480] 7f20: 60000113 ffffffff [ 1310.200153] [<c0592a64>] (__irq_svc+0x44/0x5c) from [<c0047348>] (__do_softirq+0xa8/0x2f4) [ 1310.208817] [<c0047348>] (__do_softirq+0xa8/0x2f4) from [<c0047968>] (irq_exit+0xac/0x104) [ 1310.217479] [<c0047968>] (irq_exit+0xac/0x104) from [<c000f970>] (handle_IRQ+0x54/0xb4) [ 1310.225868] [<c000f970>] (handle_IRQ+0x54/0xb4) from [<c00085b4>] (omap3_intc_handle_irq+0x60/0x74) [ 1310.235347] [<c00085b4>] (omap3_intc_handle_irq+0x60/0x74) from [<c0592c3c>] (__irq_usr+0x3c/0x60) [ 1310.244724] Exception stack(0xde0f7fb0 to 0xde0f7ff8) [ 1310.250019] 7fa0: beb94588 beb92ab8 beb9301c beb93038 [ 1310.258586] 7fc0: 00088ca0 00000140 00000160 b5440f18 00000080 b5440c64 beb92ab8 beb92fb8 [ 1310.267150] 7fe0: 4b000001 beb9267c b5f4d6a0 b5f4c8c8 80000010 ffffffff

I have done some tests and capturing to a uSD card is the easiest way to trigger XRUNS, where they occur often. Capturing to the eMMC is a little bit better. Capturing directly to tmpfs is nearly perfect, apart from very rare XRUN occurrences (10 minutes average maybe). This makes sense as EDMA is used to perform writes to the uSD and eMMC devices, so if they're being hogged with writes, then there is no time to transfer out the sound buffer and we get an overrun.

So, does anybody have ideas where to start debugging this further? I have tried to increase the buffer size from 32K up to the supposed max of 128K but I can't find where to do it... if anyone could shed any light I would most grateful, do you think increasing the buffer would solve this, as it would give more time to trigger the irq and get the data out before overrun?

I have tried multiple userspace programs to do the capture and the best so far is arecord initialized like this:

nice -n -20 arecord -D hw:0,0 -f cd -v jack-test.wav

root@beaglebone:~# nice -n -20 arecord -D hw:0,0 -f dat -v jack-test.wav Recording WAVE 'jack-test.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo DEBUG: buffer_time = 682667 DEBUG: max_buffer_size = 32768 Hardware PCM card 0 'AM335x-EVM' device 0 subdevice 0 Its setup is: stream : CAPTURE access : RW_INTERLEAVED format : S16_LE subformat : STD channels : 2 rate : 48000 exact rate : 48000 (48000/1) msbits : 16 buffer_size : 32768 period_size : 2048 period_time : 42666 tstamp_mode : NONE period_step : 1 avail_min : 2048 period_event : 0 start_threshold : 1 stop_threshold : 32768 silence_threshold: 0 silence_size : 0 boundary : 1073741824 appl_ptr : 0 hw_ptr : 0 overrun!!! (at least 221.598 ms long) Status: state : XRUN trigger_time: 1389534120.970142840 tstamp : 1389534121.191651631 delay : 0 avail : 32768 avail_max : 32768

If you need any more information or debugging output please let me know.

Regards,