multiple SD/SDIO cards on the same bus

Does anyone know if it is possible to design a device that has
multiple SD/SDIO slot
sharing the same SD bus and has two or more cards inserted and
operational at the same time?
How does one resolve the bus contention issue?

Thanks very much.

tantalum73@gmail.com wrote:

> Does anyone know if it is possible to design a device that has
> multiple SD/SDIO slot
> sharing the same SD bus and has two or more cards inserted and
> operational at the same time?
> How does one resolve the bus contention issue?
> 
> Thanks very much.
> 
http://elm-chan.org/docs/mmc/mmc_e.html

Use a seperate CS line for each device.

Be sure you have enough memory to store all the necessary information 
for each device/memory.

good luck

donald

>Does anyone know if it is possible to design a device that has
>multiple SD/SDIO slot
>sharing the same SD bus and has two or more cards inserted and
>operational at the same time?
>How does one resolve the bus contention issue?
>
>Thanks very much.
>
We are working with a partner company that offers a dual host controller
solution. Their HW combined with our SDIO stack/drivers can give you a
good solution to your problem.

Stephen Martin
Quadros Systems, Inc.

In article <1176216257.996087.33480@q75g2000hsh.googlegroups.com>, 
tantalum73@gmail.com says...
> Does anyone know if it is possible to design a device that has
> multiple SD/SDIO slot
> sharing the same SD bus and has two or more cards inserted and
> operational at the same time?
> How does one resolve the bus contention issue?
> 
> Thanks very much.

If you use the MMC bus (NOT the SPI bus), you can have multiple cards on 
the bus.  All SD cards have a unique ID, and can have an address 
assigned by the host.

At startup, all cards on the bus will be idle.
The Host sends the ALL_SEND_CID command; this causes all cards on the 
bus to start sending their unique ID, while monitoring the bus traffic. 
If a card sees a bit that is not part of its ID, it immediately stops 
sending its ID.  Thus, only one card on the bus will succeed in sending 
its complete ID.

The Host then sets a relative address for that card, at which point the 
card will no longer respond to the ALL_SEND_CID command.  This allows 
the next card(s) to be identified and addressed, and is continued until 
no more cards respond.

From that point on, the host selects a card via its local address using 
CMD 7, which places that card in the transfer state.  
When another CMD 7 is issued, if the address is not that of the 
currently active card, it automatically goes back to the standby state;
thus, only one card can be in the transfer state, so there is no 
contention.  

If you control capacitance, you can theoretically have up to 40 cards on 
the bus at once, though 10 is more typical.

--Gene