From: Andrew Kohlsmith (Mailing List Account) <aklists@mi...> - 2009-10-19 16:45:04
I'd like to add a normal-sized SD card to an expansion board I'm designing for
the Overo Earth. I see the SD signals on the expansion connector, but have a
few questions regarding it.
1) Is this SD interface also connected to the on-Overo microSD interface?
2) If so, what GPIO should I tie the SD card detect switch to so that the
Overo will see when a card is inserted into my SD card socket?
3) Am I correct in assuming that SD card signals must be level-shifted to 1.8V
for the Overo?
4) Do I need source termination on these lines? What value if so?
5) Why is there an 8-bit interface? I thought SD/MMC cards were 4-bit maximum.
I think that's it. :-)
> 1) Is this SD interface also connected to the on-Overo microSD
These are not the same - AFAIR the microSD is MMC1 while the expansion
connector is MMC3
> 2) If so, what GPIO should I tie the SD card detect switch to so that
> the Overo will see when a card is inserted into my SD card socket?
Normally the Card Detect is connected to the CD1 and CD2 pins on TPS5950 -
These are however not brought out on the Gumstix connectors => You might
need to do some SW changes in order to fix this and you can therefore choose
which GPIO might fit you best. GPIO0-31 however are in an always on
OMAP-power domain, whereas the other GPIO are in a domain which can be
switched off for power-saving, so I would choose one of the lower ones in
case you don't need them for other stuff...
> 3) Am I correct in assuming that SD card signals must be level-shifted
> to 1.8V for the Overo?
Correct - MMC3 only supports 1V8 operation
> 4) Do I need source termination on these lines? What value if so?
AFAIK: Should not be needed...
> 5) Why is there an 8-bit interface? I thought SD/MMC cards were 4-bit
Newer versions of the MMC spec (version 4 and onwards AFAIR) opens for an
8-bit wide bus
Good luck with your project
SSC Solutions ApS - Denmark - http://www.ssc-solutions.dk
Get latest updates about Open Source Projects, Conferences and News.