Nice. DMA is nice. F_CPU @ 120mhz, I ran it and saw 17.46 mbs (assuming it's really reading data )
EDIT: i read my known sector from my microSD card -- data is good
EDIT 2: I tried reading 4 sectors at a time ... nope.
I played a little bit and could also not read more than 1 sector, also changing to single bit transfer did not degrade by a factor of 4, etc. So there is a playground.
(I was using class10 64 and 128 gig SanDisks). Will try to get a faster disk.
I noticed that non-virgin part of the disk are slower and have more random read times than sectors that were never used (I believe).
Max speed I achieved was 26.7 Mbit/s (using 80 Mhz sdhc speed (240/3))
I know, that is above spec, but curiously, throughput does not scale but seem limited by uSD card.
Noted further that in Aduino Menu only the optimized code did compile/run correctly the other speed settings generated weird Serial.printf values.