Raspberry Pi questions

[Ian Lepore]

On Tue, 2012-12-25 at 21:57 -0800, Tim Kientzle wrote:
> On Dec 25, 2012, at 3:55 PM, Ian Lepore wrote:
> >>> 
> >>> This is so close to working.
> 
> I know what you mean….
> 
> I've almost got my scripts building bootable RPi images now using
> the new boot sequence that Oleksandr's been working on.
> 
> There's clearly been a huge amount of progress:  memory config
> now works, the HDMI video console works.
> 
> But I am still having a few inexplicable issues:
> 
> 1) Building U-Boot.
> 
> I'm trying to build U-Boot from the sources at
>      github.com/gonzoua/u-boot-pi.git
> They build but the result won't boot.   Can anyone
> point me to the U-Boot sources that do work?  For
> now, I'm using the binary blob that Oleksandr built.
> 
> 2) Random failure to mount root.
> 
> This is weird.  If I insert the SD card into my Mac and open
> the MSDOS partition, then eject, the card will boot (sort of,
> see below).  Otherwise, the kernel can't mount root.  I'm
> entirely baffled.
> 

I did some debugging on this today.  For me, the failure is always
associated with trying to run the card at 50mhz.  Look for this line
when it fails to boot and see if that's also the case for you.

mmcsd0: 477MB <SD 5     1.0 SN 7842 MFG 09/2007 by 111 0x0000> at mmc0
50.0MHz/4bit/65535-block

I've tracked down the underlying cause to some data corruption.  The mmc
layer sends the inquiry command to ask the card if it can do high-speed
mode, and sometimes there's bogus data in the response buffer.  It
should always be 64 bytes of zeroes, except that one bit would be set if
the card is SDHC.  I see lots of non-zero data in the first part of the
response buffer in the failure cases:

ugen0.1: <DWCOTG> at usbus0
uhub0: <DWCOTG OTG Root HUB, class 9/0, rev 2.00/1.00, addr 1> on usbus0
00648001800180018001800180030000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
mmc0: switch_res[13] 0x03

The proper response would either be all zeroes or the 0x03 byte would be
0x02 for an SDHC card.  I wonder if that non-zero data is in any way
related to a dma transfer related to initializing the usb root hub
that's happening at about the same time?

-- Ian