We've discussed this elsewhere before, but just in case it helps, the StrongARM based hardware (usually) works like this:
There is no specific buffer to hold video memory (i.e. no VRAM). The buffer that's displayed is sitting somewhere in the SDRAM.
Usually the StrongARM's internal LCD controller (and corresponding DMA) is used to transfer the contents of the "screen" from the buffer to the LCD in chunks of 16 bytes (IIRC).
The LCD's DMA is the highest priority device in the system - i.e. if the LCD is screaming for data then even the CPU is blocked out until it's serviced.
Bear in mind that normally the buffer(s) that are used for the LCD are unbuffered and uncached. They're slow to access and use. A blit to screen is really just a memcpy() to the uncached buffer that the DMA is using from whatever (usually cached) buffer that you plotted into.
The update of the LCD is limited to the refresh rate of the LCD in the device (IIRC for Ipaq's it's 70Hz).
There's no easy way of getting a vsync hooked up, so 70Hz isn't a hard limit - it's just pointless going above it.
HTH,
Ref.
