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:
- if no 2D Accelerator available or disabled (PXA270 has no 2D Acc): VideoRAM=Framebuffersize+64KB (for example: 640 x 480 x 24bit: = 640 x 480 x 3Byte + 64KB
- if 2D Accelerator available and enabled (PXA300, PXA300 XT, PXA310 and PXA320 have 2D Acc and it is enabled by default): VideoRAM=Framebuffersize x 1.5+64KB
You can set the size of the Video Memory in the Display driver registry settings. The Key is called VideoRAMsize.
Apalis Tegra / Colibri Tegra
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. Depending on how much memory intensive OpenGl application are, this value can be set lower or higher. For use-case where no OpenGl is used at all Carveout can be reduced to 8MB. (Check Toradex Task manager Tool for the current Carveout Usage of your application to better decide)
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)