Underwhelming DMA

Published on 2019-04-19 in µGame.

I finally worked on an improvement that I long wanted to do to the _stage library, which is at the heart of µGame: make the communication with the display asynchronous by using DMA. This way I can have two buffers, and calculate the contents of one of them while the other one is being sent to the display.

As a test I used the balls demo from the tutorial, but with all waiting for the next frame removed — so they move as fast as they can.

Here is how it works before DMA:

And here is how it works with DMA:

As you can see, there is barely any perceptible difference at all!

The code I wrote for this is pretty nasty and hacky, and after seeing this, I don’t think I have the heart to clean it up and send it as a pull request — it’s simply not worth it.

However, I will keep an eye for other ways of improving the firmware.

UPDATE: Yes, I made some more precise measurements as well. Running through 1000 frames of the animation took the DMA version 31.034s and the non-DMA version 32.699s. That is 32.22 fps with DMA and 30.58 fps without.

UPDATE2: I did a second test, with full-screen updates this time. 159.08s for non-DMA, versus 148.708s for DMA. That’s 6.28 fps versus 6.72 fps. Even with such a large amount of data, the difference is negligible compared to the time spent computing it.