Scratch-Pad Usage Constraints

asked May 30, 2017 in Getting started by brhansacuity
When using Embedded Wizard's Scratch-Pad feature on a system with insufficient RAM for a full frame-buffer, what are the constraints for sizing the scratch-pad?

Is there a minimum size?
Does the size need to be some multiple of the display pixel width?

In my specific implimentation I am using a 320x480x16bpp display with a STM32F412VG - so my display requires 300k of RAM while my micro only has 256k in total and I obviously need RAM for more than just the display - so I'd like to know how much leeway I have to play with in assigning memory to the scratch-pad.

1 Answer

0 votes
answered May 30, 2017 by Manfred Schweyer

According to some performance measurements on a STM32F407 there is no big performance drawback as long as the scratch-pad is at least 1/6...1/4 of the entire screen.

This means, you can reduce the effective memory for frame-buffer (= scratch-pad buffer) from 300k to 50k :-)

In principle, you can reduce the scratch-pad to one line - but then it requires 480 separate updates, which will take too long time to get acceptable frame-rates... The smaller the scratch-pad, the higher the number of partial screen updates.

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