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i.MX 8M Mini EVK Android: tinyalsa pcm_open fails to open audio device '/dev/snd/pcmC2D0c'

Question asked by Kyaw Naing on Apr 5, 2020

I am trying to implement an Android Application where it makes use of tinyalsa: pcm_open() API.  I get "cannot open device (0) for card(2): Permission denied" error when I tried to launch the application from Android Studio that attempts to open an audio stream from 8MIC-PRI-MX8 mic array board.  Note: 8MIC-PRI-MX8 mic array board appears as an alsa device "/dev/snd/pcmC2D0c" on i.Mx 8mmini EVK.


However,  the application launches fine if I build it outside of Android Studio and run it on the device with (adb) root permissions via command line.


This leads me to believe that I need to root EVK_8mm in order to gain access to "/dev/snd/pcmC2D0c" alsa device.   I started following the steps decribed here GitHub - 0xFireball/root_avd: Rooting the Android Studio AVDs 


Then, I hit a road block when I tried to run following commands:

$ adb remount
  dm_verity is enabled on the vendor partition.
Use "adb disable-verity" to disable verity.


$ adb disable-verity
Device is locked. Please unlock the device first


I came across this thread How to remount /system - 8.1 imx8m  where it provides steps to remount  the device.  I started following the steps below:


1. Unlock the device.

  a. Boot up the device.

  b. Choose Settings -> Developer Options -> OEM Unlocking to enable OEM unlocking.

  c. Enter Fastboot mode on the device. Execute the following command on the target side:

      reboot bootloader

  d. Unlock the device. Execute the following command on the host side:
      fastboot oem unlock

  e. Wait until the unlock process is complete.


Again, I ran into another problem here where fastboot was unable to find the device and indefinitely stuck in <Waiting for device>.

I updated the Device USB driver with ADB Device driver trough Windows Device Manager as suggested here How To Fix Fastboot Device Not Recognised Problem | WtfAndroid  


But, it does not solve the issue.


Just to rule out any setup issue, I tried to repeat above steps on my Google Pixel 3XL and fastboot has no problem finding the device.


Please advise.  Thanks so much.



How to remount /system - 8.1 imx8m