RT Kernel Patch on Banana Pi


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Hi there,

 

I have now finally managed to apply the RT Kernel patch on the Bananapi.

(Original Patch here: https://www.kernel.org/pub/linux/kernel/projects/rt/3.4/patch-3.4.108-rt136.patch.gz)

The patch did not work out of the box and I had a bit of hassle to fix all of the rejected bits.

 

To me the Banana Pi is best suited for audio production since it is very affoedable and it already comes with a usable audio out.

To get the full benefit of the RT kernel patch it was necessary to thrn also reduce the buffer size of the inbuilt sunxi -codec audio driver.

I can now play a synth using a buffer size of 512 samples glitch free.

 

Here are some numbers:

ansum@bananapi:~$ cat /proc/asound/card0/pcm0p/sub0/hw_params
access: RW_INTERLEAVED
format: S16_LE
subformat: STD
channels: 2
rate: 44100 (44100/1)
period_size: 128
buffer_size: 512
ansum@bananapi:~$ top

top - 14:59:12 up  1:20,  3 users,  load average: 0.35, 0.25, 0.18
Tasks: 108 total,   1 running, 107 sleeping,   0 stopped,   0 zombie
%Cpu(s):  7.1 us,  7.5 sy,  0.0 ni, 85.4 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:    734420 total,   229800 used,   504620 free,    10416 buffers
KiB Swap:   131068 total,        0 used,   131068 free.   168728 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                         
  946 ansum     20   0   32116   2328   1584 S  18.0  0.3   5:23.36 stk-demo                                        
    3 root      -2   0       0      0      0 S   3.9  0.0   2:04.22 ksoftirqd/0                                     
   11 root      -2   0       0      0      0 S   3.6  0.0   2:34.05 ksoftirqd/1                                     
   16 root     -51   0       0      0      0 S   2.3  0.0   1:13.79 irq/59-dma_irq                                  
   71 root     -51   0       0      0      0 S   2.0  0.0   0:04.19 irq/71-ehci_hcd                                 
 1207 ansum     20   0    4540   1204    840 R   1.3  0.2   0:00.46 top    

Until now I have only tested with a relatively lightweight monophonic synth. It remains to be seen how good the system performs under heavier load.

And yes: I did not install the desktop to save precious CPU cycles.

 

If anybody is interested - I have attached the patches. It is just a few file additions and replacements within Igors build system.

Make sure you have built a clean armbian image at least once before you go on and apply the patches.

Disclaimer: This is untested software and I have no Idea what it will do to your Bananapi if you decide to give it a try. 

 

Edit: It looks like am not allowed to upload attachments. Please download from here:

http://soundbytes.de/patches/armbian_BaPiRT.tar.bz2

 

Andreas

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