Interesting. It’s still very much untested which is why it hasn’t been added to libdaisy yet. I’ll be curious to see what you find.
In the project I added it for, I think I ran into some issues as well, but I was able to get stable playback/streaming with a block size of 48 samples, and 32kB reads from the SD card.
On the hardware I was working on (not daisy itself) I was able to set the SDMMC clock div setting all the way down to 1, and still have everything work reliably.
That said, I really wasn’t doing much other than playback speed adjustment and file selection. I’m not positive, but trying to write to the SD card might result in a total stall with this file… but I don’t think I tried to write either (its been a few months since I was working on it.)
I wonder if you’re doing a lot of file seeking due to the granular. I’ve noticed f_lseek can be quite slow.