I've done a lot of googling and the answer just isn't jumping out at me.
I've got a project that has two SD card slots. Access to the two cards is never simultaneous. I'm upgrading this project to an ATSAMS70N19 (mainly to get hi-speed USB), which has an HSMCI interface... but only a single one.
How can I multiplex the two card slots across this interface?
I already know that I can properly multiplex two cards in SPI mode using the !CS line (my current version of the project does that), but I am hoping to increase performance with the HSMCI interface.
I'd like to use a GPIO pin as an A/!B pin. The spec that I'm reading at least seems to suggest that I can simply switch the clock back and forth between the two cards (holding the idle card's clock either high or low) is enough to keep the idle card out of the way. Is this correct?
If this isn't good enough, how can I switch the whole bus back and forth between the two slots given that 5 out of the 6 pins are bidirectional and relatively high speed?