FreeBSD on Raspberry Pi 512MB (with U-Boot + ubldr)
ticso at cicely7.cicely.de
Tue Dec 4 12:12:04 UTC 2012
On Tue, Dec 04, 2012 at 02:43:23AM +0900, Daisuke Aoyama wrote:
> >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).
With AT91RM9200 the problem was noticeable because typically you run
the peripheral clock at 60MHz, so you can divide to 15MHz or 30MHz,
which was too high for standard, but usually worked well with most
> >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 :)
The power design of the RPI is one of the points I don't like.
> >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.
MicroSD also have 4-bit - same number of contacts.
Support for it always had been optional, that's the reason why it must be
probed and activated first.
MicroSD must support 1-bit SPI mode, which is optional on standard size SD,
but since they share common chips SD cards usually can do SPI as well.
B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
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