pito:
Some SDcards set miso (and others) open collector during the init sequence, so people indicate problems w/o a pullup (I've seen somewhere 30% cards need pullups). The internal 50k pullup (to +5V) is weak so the card's clamping diodes at the inputs will probably survive (will pass the current to the card's 3V3 thus limit input voltage to 3V3+Vfd).
So do you suppose I could enable the 50K pullup during the init sequence, and then disable it from that point on? Would that even be worthwhile, from the standpoint of trying to protect that diode? Which portion is considered the init sequence? Everything in power_on() up to and including the 80 dummy clocks perhaps?
I guess I can try it and see what happens...