Vsync for ipodnano2g

[thefirstm]

I was wondering if someone might be able to implement display vsync for the ipodnano2g.  I asked on IRC if this would be possible, and saratoga said that it probably wouldn't be very difficult.  I looked at the s5l8700 datasheet and it has information about display vsync, but I do not know how to write hardware drivers and could not figure out the LCD driver.  TheSeven, you appear to be an expert on the ipodnano2g.  Do you have any comments?

[saratoga]

I think the vsync pin mentioned in the datasheet is something unrelated to what you want to do. 

As I understand it, what you actually want to do is just synchronize updates to the frame buffer with updates to the LCD screen.  Thats probably not difficult to implement (if its not implemented already), but I don't know much about the drawing code in rockbox.

[thefirstm]

You are right, I want to sync the framebuffer and LCD.  The OF does this, so it has to be possible.

[saratoga]

You are right, I want to sync the framebuffer and LCD.  The OF does this, so it has to be possible.

Sure its possible, its just a software operation.  Have you checked if its already implemented?

Edit:  looking at the driver it doesn't yield or use DMA for an LCD update, so I think it should be synchronized.  At least I can't see any way for the buffer to change during an LCD transfer. 

My guess is you see tearing because of some bug in the doom drawing code.

[thefirstm]

No, everything tears, not just doom.  A good example would be the Oscilloscope plugin, where the tearing is very obvious as the red line scrolls across the screen right after the plugin starts.  It appears that the LCD is being updated while data is being blitted into the framebuffer, instead of waiting for the vblank interval.