Video Memory is a special part of the RAM which is controlled by the display driver. This memory can be used by the hardware graphics acceleration unit on the PXA3xx chips.
It is required to reserve the space for the video memory, because the memory needs to be physically contiguous. In case if the Video Memory is already full, the system will allocate also device dependent bitmaps in the normal RAM. That means the GCU cannot be used for graphic acceleration.
There is video RAM size by default:
You can set the size of the Video Memory in the Display driver registry settings. The Key is called VideoRAMsize.
On these modules the video RAM is part of the Carveout memory.
On the Colibri T20 the default Carveout size is 64MB. It can be reconfigured in the Config Block.
On the T30 modules Carveout memory is not used for video ram in images newer than V1.2. The default value for T30 is set to the minimum required size, which is 2MB.
pex.carveout = 64 (Carve out Size in MB)