This post is the third in a series looking at the
design and implementation of my Glitch demo and the
m4vgalib code that powers it.
In part two, I showed a fast way to push pixels out of an STM32F407 by getting
the DMA controller to run at top speed. I described the mode as follows:
It just runs full-tilt, restricted only by the speed of the “memory” [or
memory-mapped peripheral] at either side…
But there’s a weakness in this approach, which can introduce jitter and hurt your video quality. I hinted at it in a footnote:
…and traffic on the AHB matrix, which is very important — I’ll come back
Quite a bit of m4vgalib’s design is dedicated to coordinating matrix traffic,
while imposing few restrictions on the application. In this article, with a
minimum of movie puns, I’ll explain what that that means and how I achieved it.