[maemo-developers] DSP framebuffer access

[From: Simon Pickering]

> The screen changes colour, though it appears that the screen updates 
> only happen from time to time so exactly what changes colour, which 
> colour it turns, and when is a question of luck.  I'm not sure how 
> one should force an update (And perhaps this will have to be from the 
> ARM side, I don't know). Any suggestions?

Well no real improvement, but perhaps I need to produce a window that 
won't auto-refresh itself.

Anyway I should add that it looks like one is supposed to call 
fb_lock() before fiddling with the framebuffer and fb_unlock() after 
one has finished. These don't do anything exciting, they just 
encapsulate a semaphore used to control access to the framebuffer from 
the DSP-side.

Of more interest is the kfunc() function. I believe that the following 
should issue a framebuffer update command:

kfunc(MBCMD_KFUNC_FBCTL, OMAP_DSP_MBCMD_FBCTL_UPD, 0, 0);

There's another function that can be called using kfunc() with a 
different define: OMAP_DSP_MBCMD_KFUNC_AUDIO_PWR which results in a 
call to the mbx1_kfunc_audio_pwr() function on the ARM-side. Depending 
on what other parameters one passes, the audio hardware can then be 
powered up or powered down (2 settings).

With regard to framebuffer access from the N800's DSP. I'm getting the 
following error: "exmap page overlap!" (from dsp_mem.c in the 
plat-omap/dsp/ dir of the kernel code).

It appears that mapping the framebuffer requires its own memory 
section. I'm not sure if there's any room left on the N800 to fit one 
of these. With that said, I may be wrong about this as I've not really 
looked at it yet.

Night all,


Simon