The MMCplus Application note (version 4): http://www.mmca.org/compliance/buy_s...MMCA050419.pdf says:

"The initialization procedure of MMCplus is equivalent to that of cards by standard version 3.31. The major difference is that any dedicated MMCplus host application is restriced to have only a single card slot (in order to cope with the increased frequency requirements)."

However it looks like standard MMC might be ok. Does anyone know if this is supported in the kernel?

The pinout for standard MMC according to the specification summary is:

Pin No. Name Type Description
1 RSV NC Reserved for future use
2 CMD I/O/PP/OD Command/Response
3 VSS1 S Supply voltage ground
4 VDD S Supply voltage
5 CLK I Clock
6 VSS2 S Supply voltage ground
7 DAT2 I/O/PP Data
Table 1: MultiMediaCard pad definition

from: http://www.mmca.org/compliance/buy_s...mary-v3.31.pdf

Doesn't have chip select, so may be it's done in the protocol?

I think there is a little confusion here. There are three modes of communication over SD/MMC slot.
- SPI - supported in theory by both mmc and sd cards, pins are explained for this mode on picture already mentioned, useful for some ancient hardware that can do only SPI
- MMC mode - only mmc cards can do this, preferred mode for MMC cards
- SD mode - only sd cards can do this, preferred mode for SD cards

Both SD and MMC modes are supported by N770 linux kernel, SPI not (for OMAP driver). Not sure about SD but at least MMC can have multiple cards connected to same bus (i.e. same pins). Cards have unique IDs and all listen to commands and only the one with correct ID responds to the command. SD maybe too (or maybe not) but anyway this mode is not regulary used and is now deprecated by MMC association. MMC high speed modes defined in MMC 4.x require only one card to be present. Also I think support for more cards is to be removed from linux kernel since it is really not used and only complicates things.

So to sum it up you may now connect more MMC cards to same pins but they will run in legacy MMC mode (max 20Mhz) and there may be bugs since this was never widely used. I'm also not sure about power requirements of such solution (i.e. if the slot in n770 can cope with powering two cards at once).
chip select is only for SPI mode, we probably don't want to use this and the pin is missing in N770 slot anyway. As for SD driver it is already present in the kernel.
No the support is not completely present due to missing hardware. If I understand it correctly having support for two slots in OMAP1710 CPU is not enough. You need additional hardware for powering up and driving the slot. Such second chip is missing for the second slot and if present in must be controlled from SD/MMC driver in linux kernel (i.e. powered up and down at right time) for the slot to work. Search this forum for both n770 and n800 schematics and see how SD/MMC slots are wired.

I think there are only two easy options to have cards over 2GB (current mmcmobile available maximum)
- wait for bigger mmcmobile cards (no problem with support for them)
- wire up >=4GB SD (regular,mini or micro) or MMCplus card to the slot.

Thanks for the info. I've connected 2 MMC cards ( http://linuxjunk.blogspot.com/2007/0...dual-mmcs.html ). And yep, they appear to work ok. Mind these are only 64 and 16mb cards so I guess I'm not drawing too much power from the 770.

However connecting a SD and an MMC at the same time only detected the SD. I thought SD should fall back to MMC mode if SD mode isn't supported but perhaps it's not supported for multiple devices. I might try connecting two SD cards and see what happens.

The stock tablet 2006 kernel? Is there any way to tell if the device is running in SD or MMC mode. All devices appear as mmcblkX to me, which doesn't tell me much.

ok, I guess the additional hardware could be added and the kernel patched if the pins are actually exposed somewhere. There are some pins next to the battery but I'm guessing those are probably JTAG? If anywhere they are probably under the metal shielding, I don't really fancy removing that right now.


Thanks for your help.

Didn't work, I get a bunch of CRC errors on dmesg and no cards detected.

As explained twice in this thread SD cards don't understand MMC protocol so the can't fall back to anything.

Ah ok, I guess I got confused with them both being able to fall back in to SPI mode or something.

Yes. it is same driver as MMC. There is no high speed SD (50Mhz) and no SDHC support in stock tablet kernel but otherwise it is there.
Well with SD card inserted it is in SD mode, check is done at runtime.
You can browse source here http://lxr.linux.no/source/drivers/mmc/?v=2.6.18
main sources are mmc.c and mmc_block.c, OMAP specific lowlevel driver is in omap.c
Thanks for your tests. I was not sure more mmc cards would actually work, it is good to know it is possible and working.

A link:
http://focus.ti.com/general/docs/wtb...contentId=4670

However, that is not to say that there are traces going somewhere on the PCB.

I think an idea, that I have not seen in this thread, would be to make an insertable RS-MMC to SD adapter. Use a ribbon cable or flexible PCB or the like and mount a socket on the outside of the case. Or, if there is room within the shell mount the SD card somewhere within.

Hrmmm...

eb

The link to the pictures of the mod came out with a "0" instead of a "-" when I did a cut and past. The link that works is:

http://linuxjunk.blogspot.com/2007/0...dual-mmcs.html

It sure looks interesting! Yes, a little flex circuit sneaking past the lever-cover to some sort of expansion pack sounds interesting. To keep it in place all the time would require some sort of leather style booklet case with a reinforced front to protect the LCD. That way there could be a compartment or flap somewhere in the case for the external module(s) and the reinforced foldover front would do the job of the metal slipcover in protecting the screen. No magnet, though. It would be best for those not requiring super speed, just more storage, like MP3 files for example. Then of course there is always the possibility of a custom ASIC chip to serve as an MMC to Compact Flash Hard Drive interface. Maybe some kernel tweaks to make it work, too. :-)

I wonder modifying a small MicroSD to SD adapter would work. Surfing the net I come across a cheap adapter like this:



One side of the adapter is the USB insert, and the other side is SD. Without the USB portion the length is around 21mm, slightly longer than the 18mm RS-MMC standard. Someone reported that it's a bit thicker than the normal SD card, and if you crack open the case it looks like this:



So if the case is removed, usb part is cut off, and glue a MicroSD onto the PCB, it might be thin enough and small enough to insert into 770's RS-MMC socket.

PS I don't want to spam the forum, so if you want to know where to buy it, google "Worlds Smallest 2-in-1 Trio TransFlash USB Card Reader".