Re: 2GB MMC/SD cards

Pierre Ossman
2006-06-03T21:11:30Z

Russell King wrote:
> The specs I have say the following about WRITE_BL_PARTIAL:
>
> Samsung (csd v1.2 mmc v4.1):
> 0: means that only the WRITE_BL_LEN block size can be used for block oriented data write.
> 1: means that smaller blocks can be used as well. The minimum block size is one byte.
>
> Sandisk (csd v1.1 mmc v1.4):
> 0: means that only the WRITE_BL_LEN block size can be used for block oriented data write.
> 1: means that smaller blocks can be used as well. The minimum block size is one byte.
>
> The wording is identical from these two differing manufacturers, so I
> suspect it comes from the original spec.
>
>

A sponsored copy of the official spec. is long overdue...

> I am not aware of any bug reports in this area, so I can't comment. In
> fact, I see very few reports of MMC problems at all, so I just assume
> that it merely works. Unless folk report bugs to me...
>

For some reason, I get lots. :)
It's probably because I am the maintainer for the only two drivers for
hardware that is found in laptops. More average Joes in that market.

Like you, I unfortunately haven't got any of these cards for myself. But
I've gotten reports of both that "other" readers use 512 bytes[1],
regardless of WRITE_BL_LEN, and that cards that have WRITE_BL_LEN of
1024 and _not_ partial, still work just fine with 512 bytes[2].

[1] http://list.hades.drzeus.cx/pipermail/wbsd-devel/2006-May/000485.html
[2] http://list.drzeus.cx/pipermail/sdhci-devel/2006-May/000826.html

> I don't know what to do about this since I don't have any cards and
> I've not seen any bug reports to investigate what's going on. So I'm
> just going to say "the code as it stands is correct as to my best
> knowledge, please provide details of it's failings."
>
>

I'll point people to your patch then and ask them to have you as a cc.

Rgds
Pierre