SD-cards for zynthian V5

[jofemodo]

I’m adding this link here just for easy future reference:

Zynthian 5.1 kit does not boot - faulty SD card cable

For the curious: The protocol used by SD-cards is synchronous, Each package is ACKed after sending and the full process must happen in one clock tick, so the signal MUST travel twice the cable length in one clock tick. Indeed, you need some margin to get things working stable. You can do the maths for “standard” transmission speeds in PCB tracks (about 50% of light speed, i.e. 15 cm/ns). Asking the IA, she tells: Track Length Guidelines by Protocol SD Card Mode / Type Frequency Max Track…

Regards,