Am 31.01.2014 um 10:49 schrieb Dr. H. Nikolaus Schaller:
Hi, triggered by the proposal and discussions on the forum to add a combined SIM/SD-Reader for another internal Micro-SD card (which I find a nice idea):
http://boards.openpandora.org/topic/14698-overview-of-soc-options/?p=309418
I have checked the mechanical fit - and there is no problem to add such a piece.
For the electrical/logical interface, I have analysed all the TRMs and data sheets for understanding the limitations of the SDIO controllers of the OMAP5 [2].
We have no problems running one internal eMMC, one bootable high-speed SD slot, a second non-bootable standard speed SD slot and WLAN.
But we have a problem to interface a third Micro-SD slot because the SDIO5 port is n/a on the 5432 chip.
Options to solve this are
- replace the eMMC by the Micro-SD (which will have a much lower speed limit!)
- interface WLAN though SPI (is not optimal for 802.11n) and use the SDIO3 port
- interface WLAN through (internal) HS-USB (likely to draw more power and needs different chipset/module) and use the SDIO3 port
- interface the Micro-SD slot (or even the second full speed) slot though USB (needs a probably power hungry SD-USB controller chip like [1])
With such a chip http://www.genesyslogic.com/jp/product_view.php?show=7 we could also think about this configuration:
SDIO1: SIM/Micro-SD (used only for factory programming or unbricking or by user if he/she likes) SDIO2: internal eMMC SDIO3: WLAN SDIO4: unused HSUSB: 2 full sized SD slots which magically mount as USB memory drives - without any need for an OMAP SD driver; but they are only bootable if U-Boot in eMMC recognizes them
But let me check first that we have enough USB ports for any such configuration...
It is sort of a puzzle of limitations :)
In any case only the master SD slot is bootable and not the Micro-SD slot (even if connected through USB because the Boot ROM can't handle USB memory for booting).
BR, Nikolaus
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