fbset in triple buffering usage

Daniel70334

We have DM816x and DM814x EVMs in-house for our current project. I've been looking into things that need to be changed when the output resolution changes on-the-fly, including the frame buffer setup. I have a basic question about this line from /etc/init.d/pvr-init in the EZSDK:

# Try to enable triple buffering when there's enough VRAM
fbset -vyres $(expr $YRES \* 3)

I haven't been able to find any explanations as to how setting the fbdev's virtual yres enables triple buffering. Is this an OpenGL thing? A Qt thing? Is the EZSDK's matrix app doing something special when vyes is a multiple of yres?

over 13 years ago

0 Prathap Srinivas over 13 years ago

TI__Expert 5000 points

Hi Daniel,

Setting FLIP mode in /etc/powervr.in leads to the ping ping-pong scheme being used for graphics(openGLES) updates. The numbe of buffers created depends on the vram size allocated in bootargs.

When using Front mode in /etc/powervr.ini, SGX fb updates happen directly on single framebuffer (front buffer). Not really recommended except for SGX benchmarking as it will result tearing artifacts at high resolution and frame rates.

Setting flip mode in /etc/powervr.ini, uses ping-pong scheme for graphics updates and this is the default EGL library used if /etc/powervr.ini is not present.

Modify the powervr.ini file under the <your_target_file_system>/etc to select between the FrontEGL or FlipEGL mode.

Flip support requires increasing the virtual yres size in fb0 plane and allocating appropriate memory for framebuffer.

Hence fbset command may be used to increase the virtual yres size in fb0 plane. The vyres size needs to be set to three times the height of the screen size for triple buffering.

Please go through below links for more details if required -

http://processors.wiki.ti.com/index.php/GSG:_OMAP35x_Graphics_SDK_Additional_Procedures#Switching_between_FrontEGL_and_FlipEGL_Modes

http://processors.wiki.ti.com/index.php/SGXDbg#WindowSystem

Thanks,

Prathap.

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fbset in triple buffering usage