FreeBSD on Raspberry Pi 512MB (with U-Boot + ubldr)

Daisuke Aoyama aoyama at
Mon Dec 3 17:43:13 UTC 2012

> SD 2.0 upped the limit to 50mhz, but you can't set the bus to run that
> fast until you've probed the card and determined that it supports SDHC.
> The signaling standard is actually different between 1.x and 2.x in SDHC
> mode (there are differences in the relationships between rise/fall/hold
> times above 25mhz).  That's why old Atmel hardware can't do SDHC 50mhz
> even though the microcontroller can run the bus at 50mhz -- it does so
> with the 1.x signal timings (it was pretty sneaky of them to adverise
> mmc/sd up to 50mhz knowing that running the bus that fast was just a
> violation of the SD 1.x spec, which is all they really support).
> I've heard that SD 3.x allows for bus speeds of 100mhz and higher, but
> only on SDXC cards.  I'm hand-waving a bit here because I haven't gotten
> to work with hardware that new yet.

Yes, you are right. But my card don't work with 50/100MHz 4bit mode.
And, many users have reported don't work.
In my case, the command under 50/100 was reported CRC error, etc.

FYI, the cards require 2x max power consumption when HS mode is enabled.
There is another factor the card runs at HS on RPI.
I imagine my card eats more power :)

> Bus speed is independant of the 1/4/8 bit datapath (well, at least in
> the SD specs up through 2.0, after that I'm not sure).

AFAIK, micro SD cards use 1bit.

If you are interesting about SD card, you can get Simplified Version of the 
Physical Layer Specification

Daisuke Aoyama

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