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K70 LCDC maximum display rate/frames per second (fps)

Question asked by Leo Costello on Jan 28, 2017
Latest reply on Feb 16, 2017 by Jonathan Iglesias

Hello all,

 

What is the maximum frame rate (frames per second) that a K70 running at 120 MHz can achieve? Our display resolution is 800x480 with a color depth of 24 bpp, for a total of 1,152,138 bytes per frame (~1 MB). I'm assuming multiple frame buffers can be used, and that the pointer to the active buffer can be changed at the end of each display refresh cycle. If two frame buffers are used, the inactive frame can be written during the screen refresh time. So does that mean that the maximum display rate is determined by the speed of a 1 MB DMA write to the inactive buffer?  If the DMA clock is 30 MHz (120/4 MHz) and 4 bytes are written each clock cycle, 1 MB would be written in 8.3 msec. So a new frame would be available every 8.3 msec, which is a rate of 120 fps. For our display the maximum refresh rate (determined by the display's maximum pixel clock) is 65 Hz, which would therefore be the limiting factor (65 fps is less than 120 fps). And the effective "optical" video rate would be determined by the response time of the pixels, which with our display is at most 35 ms. This would further limit the possible video rate to about 28 fps (1/35 ms).

 

Does the above make sense?

 

Thanks,

Leo

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