Wednesday, September 21, 2011

SD card - again

A little update -
It seems incremental updates DO work. That's good news!
I'm however quite stunned that the various parts of the reading take so much time...

Loop 1 : Starting...18.467 ms
Loop 2 : Read 512 Bytes, 16.303 ms
Loop 3 : Read 512 Bytes, 16.301 ms
Loop 4 : Read 512 Bytes, 16.309 ms
Loop 5 : Read 512 Bytes, 16.300 ms
Loop 6 : Read 512 Bytes, 16.304 ms
Loop 7 : Read 512 Bytes, 16.307 ms
Loop 8 : Read 512 Bytes, 16.303 ms
Loop 9 : Read 512 Bytes, 16.301 ms
Loop 10: Closing! 1.779 ms

Each loop requires a 10 ms SD.begin() call. So in practice, a data read is actually 'only' 6 ms.
So there's more to be done, but as I said - incremental updates are a good thing!



After a little tweaking I'm able to have a (somewhat) flickerfree loading in the background.
It runs at about 40 Hz and the video is loaded at between 5 and 10 fps depending on blocksize.

So, I can either A) limit the 110 Hz refresh to match the lower loading Hz, or B) Switch to fullscreen@40Hz when displaying video. Or probably C) only show animations on 2/3 of the display like newer Stern games. Or even D) depending on type of animation, load the frames in the background and display the animation when ready. This requires a maximum of 30 frames animation length since that's all the RAM I've got available.

All of the above assumes 16 color video. Smaller video size or fewer colors would contribute to a faster refreshrate.

Hopefully I can tweak the SD loading even more to bring up the refresh rate, since it also controls the brightness of the screen.

No comments:

Post a Comment