There has been a great deal of buzz lately over an article published a few days ago on Pocket PC Thoughts pointing out that PXA250 XScale processors have support for SDIO built into them. This means it might be possible to make every handheld with a PXA250 XScale processor and an SD slot SDIO capable if drivers were written to support it.
Of course, this is of enormous interest to owners of HP iPAQ h1910, Dell Axim X5, and other handhelds with this processor that don't offer SDIO support. Many believe the h1910 would be the perfect Pocket PC if it included SDIO.
Unfortunately, the situation isn't as rosy as some hope. First off, the default implementation is a 1-bit bus speed, called SD Narrow, which is far below the 4-bit bus speed, called SD Wide, normally offered on handhelds with SDIO. However, this isn't a crippling limitation; MMC Cards transfer data at the same rate.
Unfortunately, it's possible that for hardware reasons SDIO won't work at all on some handhelds. For SDIO to work, the SDIO slot's Interrupt Request (IRQ) pin on the XScale processor must be connected to a General Purpose Input/Output (GPIO) pin. If this hasn't happened, SDIO won't work on the handheld, even if drivers are written.
At this point, it is not known if any handhelds that use the PXA250 XScale processor have the pins wired in such a way that SDIO is possible. However, research in this area is going on right now.
By default, SD slots can handle memory cards. There is also a standard, called SDIO, that has been created to allow these slots to handle other types of cards. This includes wireless networking cards, digital cameras, presentation tools, and more.
Until recently, SDIO support was almost inconsequential, as very few SDIO peripherals were on the market. But several companies have recently announced plans to release SDIO wireless networking cards, which has greatly increased public interest in the standard.
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