Parallel/simultaneous recording (using threads) on multiple channels using M-Audio M-Track Eight

[SREEKANTH SREEKUMAR <sreekanth1989@xxxxxxxx>]

I have M-Audio M-Track Eight, a USB based soundcard that I use to play and record audio files using a python based tool I wrote. My device definitions in .asoundrc looks like this:

pcm.!default {
    type plug
    slave {
       pcm "hw:1,0"
    }
}

ctl.!default {
    type hw
    card 1
}

pcm_slave.m-audio_m-track_eight_1 {
    pcm "hw:1,0"
    channels 8
    rate 44100
    buffer_size 4096
    period_size 1024
}

pcm.outch1 {
    type dshare
    ipc_key 1111
    slave m-audio_m-track_eight_1
    bindings [ 0 ]
    hint.description "M-Audio M-Track Eight output/playback channel 1 (from output port 1)"
}

pcm.inch1 {
    type dsnoop
    ipc_key 2111
    slave m-audio_m-track_eight_1
    bindings [ 0 ]
    hint.description "M-Audio M-Track Eight input/capture channel 1 (from input port 1)"
}

pcm.outch2 {
    type dshare
    ipc_key 1112
    slave m-audio_m-track_eight_1
    bindings [ 1 ]
    hint.description "M-Audio M-Track Eight output/playback channel 2 (from output port 2)"
}

pcm.inch2 {
    type dsnoop
    ipc_key 2112
    slave m-audio_m-track_eight_1
    bindings [ 1 ]
    hint.description "M-Audio M-Track Eight input/capture channel 2 (from input port 2)"
}

pcm.outch3 {
    type dshare
    ipc_key 1113
    slave m-audio_m-track_eight_1
    bindings [ 2 ]
    hint.description "M-Audio M-Track Eight output/playback channel 3 (from output port 3)"
}

pcm.inch3 {
    type dsnoop
    ipc_key 2113
    slave m-audio_m-track_eight_1
    bindings [ 2 ]
    hint.description "M-Audio M-Track Eight input/capture channel 3 (from input port 3)"
}

pcm.outch4 {
    type dshare
    ipc_key 1114
    slave m-audio_m-track_eight_1
    bindings [ 3 ]
    hint.description "M-Audio M-Track Eight output/playback channel 4 (from output port 4)"
}

pcm.inch4 {
    type dsnoop
    ipc_key 2114
    slave m-audio_m-track_eight_1
    bindings [ 3 ]
    hint.description "M-Audio M-Track Eight input/capture channel 4 (from input port 4)"
}

pcm.outch5 {
    type dshare
    ipc_key 1115
    slave m-audio_m-track_eight_1
    bindings [ 4 ]
    hint.description "M-Audio M-Track Eight output/playback channel 5 (from output port 5)"
}

pcm.inch5 {
    type dsnoop
    ipc_key 2115
    slave m-audio_m-track_eight_1
    bindings [ 4 ]
    hint.description "M-Audio M-Track Eight input/capture channel 5 (from input port 5)"
}

pcm.outch6 {
    type dshare
    ipc_key 1116
    slave m-audio_m-track_eight_1
    bindings [ 5 ]
    hint.description "M-Audio M-Track Eight output/playback channel 6 (from output port 6)"
}

pcm.inch6 {
    type dsnoop
    ipc_key 2116
    slave m-audio_m-track_eight_1
    bindings [ 5 ]
    hint.description "M-Audio M-Track Eight input/capture channel 6 (from input port 6)"
}

pcm.outch7 {
    type dshare
    ipc_key 1117
    slave m-audio_m-track_eight_1
    bindings [ 6 ]
    hint.description "M-Audio M-Track Eight output/playback channel 7 (from output port 7)"
}

pcm.inch7 {
    type dsnoop
    ipc_key 2117
    slave m-audio_m-track_eight_1
    bindings [ 6 ]
    hint.description "M-Audio M-Track Eight input/capture channel 7 (from input port 7)"
}

pcm.outch8 {
    type dshare
    ipc_key 1118
    slave m-audio_m-track_eight_1
    bindings [ 7 ]
    hint.description "M-Audio M-Track Eight output/playback channel 8 (from output port 8)"
}

pcm.inch8 {
    type dsnoop
    ipc_key 2118
    slave m-audio_m-track_eight_1
    bindings [ 7 ]
    hint.description "M-Audio M-Track Eight input/capture channel 8 (from input port 8)"
}

But, with the above, I figured out that it is not possible to play and record on multiple channels simultaneously. I do this by executing the following command in separate threads in a python script:




arecord -D plug:"+str(in_id)+" -c 1 -d "+str(duration)+" -f S16_LE -r "+str(rate)+" "+rec_filename




where `in_id` is the input channel variable that I pass to each of the threads.

More specifically, the `arecord` throws the error:

"ALSA lib pcm_dsnoop.c:606:(snd_pcm_dsnoop_open) unable to open slave

arecord: main:722: audio open error: Device or resource busy"

I tried to debug this by running `lsof /dev/snd/pcm*` right before I start recording using `arecord` in my record function in the program, I see the following:


    COMMAND   PID        USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
    aplay   12236       user4  mem    CHR  116,3           493 /dev/snd/pcmC1D0p
    aplay   12236       user4    4u   CHR  116,3      0t0  493 /dev/snd/pcmC1D0p


Then I came across the following two posts:
https://www.spinics.net/linux/fedora/alsa-user/msg14391.html
https://askubuntu.com/questions/27416/record-8-separate-line-in-channels-from-m-audio-delta-1010-card


The user in the first post seems to have solved by adding the following to his .asoundrc:

pcm.D44_cslave {
	type dsnoop
	ipc_key 223456
	slave {
		pcm		"hw:0,0"
		rate		48000
		period_time	0		# in microseconds
		buffer_size	256		# in bytes
		period_size	64		# in bytes
		channels	4
		format		S32_LE
	}
	bindings {
		0 0
		1 1
		2 2
		3 3
	}
}

pcm.D44_ch12_capture {
	type		plug
	ttable.0.0 1
	ttable.1.1 1
	slave.pcm	D44_cslave
}

pcm.D44_ch34_capture {
	type		plug
	ttable.0.2 1
	ttable.1.3 1
	slave.pcm	D44_cslave
}
as mentioned in this message of the particular thread:
https://www.spinics.net/linux/fedora/alsa-user/msg14409.html

The second user on the other hand appears to have solved it by modifying his .asoundrc as follows:


pcm.capt {
       type dsnoop
       ipc_key 223456
       slave {
               pcm "hw:0,0"
               rate 8000
               period_time 0
               period_size 320
               channels 12
               format S32_LE
       }
}

pcm.c1 {
    type plug
    ttable.0.0 1
    slave.pcm capt
}

pcm.c2 {
    type plug
    ttable.0.1 1
    slave.pcm capt
}

pcm.c3 {
    type plug
    ttable.0.2 1
    slave.pcm capt
}

pcm.c4 {
    type plug
    ttable.0.3 1
    slave.pcm capt
}

pcm.c5 {
    type plug
    ttable.0.4 1
    slave.pcm capt
}

pcm.c6 {
    type plug
    ttable.0.5 1
    slave.pcm capt
}

pcm.c7 {
    type plug
    ttable.0.6 1
    slave.pcm capt
}

pcm.c8 {
    type plug
    ttable.0.7 1
    slave.pcm capt
}


Now, my questions are : 
1. What could be the right configuration for me if I want to use the input and output channels exclusively for capture/record and playing respectively? Also, are my `arecord` and `aplay` commands fine? 
2. If the error shows that dsnoop is indeed busy, then why was it not being shown in the output of `lsof /dev/snd/pcm*`. The error clearly says there is a definite problem with `dsnoop`, does that mean that it is not meant for simultaneous/multi-channel recording? I mean is there a conflict between `dsnoop` and `dshare` or if multiple instances of `dsnoop` is what is causing the problem?


It would be of great help if someone could educate me on the above and help me out with the configurations.

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