Does anyone have sdio protocol experience?

[Alan Nishioka]

I am trying to write an sdio host controller. sdio is an extension to
the sd/mmc protocol used on memory cards. It is used for pda peripheral
devices, for example.

Note that this question is about the sdio protocol, not the spi protocol
that is part of the sdio/sd/mmc specification.

I am able to send and receive a response on the cmd line, but when I
send or request data, I never see it on the data lines.

Specifically, cmd52 works for both read and write and I get the correct
response. But while cmd53 responds on the cmd line, I never see
activity on the data lines.

Does anyone know what I am missing?

Alan Nishioka
al...@nishioka.com

[Alan Nishioka]

I seem to be talking to myself, but I do that a lot anyway, so I will
answer my own question.

You need to enable the function to drive the data lines. Specifically,
bit1 of address 0x0002 in the CCCR must be set.

If you don't do this, you will be able to send and receive on the cmd
line, but not on the data lines.

Incidentally, opencores has several sd/mmc projects but they *all* only
operate in spi mode.

Alan Nishioka
al...@nishioka.com