Skip to content

High Capacity SD and MMC support

In our last episode, I talked about how I was planning to add support for SDHC cards to Linux, and I’m happy to report that Pierre has accepted my changes into his tree and pushed them out to -mm; hopefully they’ll be in mainline for 2.6.21.

Now, if you have any SD/MMC reader supported by the kernel, it will be able to grok SDHC cards. In theory, this also includes the shiny new Nokia N800 – although no one has recompiled a new kernel for it yet to verify this – I hope to get a hold of one in the near future to test for myself. :-)

My next target is High Capacity MMC cards. These don’t have any fancy new branding like the SD ones do – and frankly, I think that to be a mistake as the compatibility story is equally convoluted – the only way to know for sure is if they are described as conforming to the MMC 4.2 spec. The changes to handle these cards are exactly equivalent to those for SDHC, and I have Samsung to thank for documenting that – given that there’s no 4.2 Application Note available from the MMCA. A small piece of reverse-engineering is required to work out where exactly the card capacity is stored under the new scheme, but that was always the easiest part to work out. Now I just have to get my hands on one of these cards!

Pierre is currently undertaking a major restructuring of the MMC subsystem so that we’re better placed to add support for SDIO and CE-ATA and I hope to help out with those efforts as I can.

{ 9 } Comments