Raspberry Pi No Login

[Ian Lepore]

On Sat, 2013-02-09 at 17:04 -0800, Oleksandr Tymoshenko wrote:
> On 1/30/2013 2:51 PM, Oleksandr Tymoshenko wrote:
> > On 1/30/2013 2:25 PM, hiren panchasara wrote:
> >> On Wed, Jan 30, 2013 at 9:15 AM, Tim Kientzle <tim at kientzle.com> wrote:
> >>> On Jan 30, 2013, at 7:42 AM, Neal Nelson wrote:
> >>>
> >>>> HI.
> >>>>
> >>>> I'm able to build a bootable FreeBSD image using the beaglebone 
> >>>> scripts, which I understand is the accepted way at the moment.
> >>>>
> >>>> The problem I have is that everything seems to be going nicely, but 
> >>>> I never get a login prompt. The last thing I see, after the ssh key 
> >>>> generation stuff, is a line showing the date, then nothing. This is 
> >>>> true using Current as of today (2012-01-30).
> >>>>
> >>>> I've had this problem for some time now as every image I build 
> >>>> using this process has the same problem. If anyone has an idea as 
> >>>> to what I'm doing wrong, I'd be very grateful.
> >>> Look at the kernel boot messages for the SD card
> >>> check.
> >>>
> >>> Is it probing at 25MHz or 50MHz?
> >>>
> >>> I haven't tried RPi in a little while, but last time I did
> >>> there was an erratic bug which caused the SD card
> >>> to sometimes get probed at 50MHz and be non-functional.
> >>>
> >>> I believe some people worked around this by trying
> >>> different cards or maybe it's been fixed in the
> >>> SD driver by now?
> >> Not sure if its fixed in the driver now but I got around the frequency
> >> problem by the patch available at:
> >> http://www.peach.ne.jp/archives/rpi/patch/
> >>
> >> Basically its setting freq to 25MHz instead of default 50MHz in
> >> bcm2835_sdhci.c
> >
> > The patch works around the issue although it does address several 
> > issues with FreeBSD's
> > generic mmc driver. Namely: driver does not check for return value for 
> > functions that read
> > card's CSD, SCR or the result of switch command. CSD and SCR register 
> > contain card-specific
> > information drivers uses to tune its operations. So when register read 
> > command silently
> > fails driver uses partially valid data and hence its behavior might or 
> > might not manifest
> > problems.
> >
> > Now the interesting part is why these commands fail. SDHCI controller 
> > returns Data CRC
> > errors when executing them. It happens fairly early in initialization 
> > sequence so at that point
> > card operates at 400KHz and should not have problem like this.
> 
> Today I went all scientific on this issue and plugged logic analyzer
> to SD card using SparkFun's SD Sniffer[1]. What I found was that on
> power up SDHCI controller starts operating at frequency of 190KHz but
> shortly after it, before any data is read via DATA line, it switches to
> 8MHz. So I capped minimum frequency for SDHCI driver at 8MHz and got
> RPi into endless reboot cycle. Lo and behold: it's been almost two
> hours and so far no Data CRC Error interrupts.
> 
> Patch: http://people.freebsd.org/~gonzo/arm/patches/rpi-sdhci.diff
> 
> Description:
>      - Do not silently ignore failure of "Read CSD" and "Read SCR"
>        commands since data returned by them is essential for further
>        initialization
>      - Properly calculate minimum frequency for SDHCI 3.00 and higher
>      - Add new method to SDHCI interface for setting driver-specific
>          minimum frequency. Provide default implementation.
>      - Cap minimum frequency at 8MHz for Raspberry Pi's SDHC
> 
> I'd appreciate reviews and testing. There is one debug printf that
> will be removed from final version.
> 
> [1] https://www.sparkfun.com/products/11468
> 

I may not be understanding what you mean about the 8mhz clock, but if
that refers to the speed on the sd/mmc bus itself, that sounds like a
violation of the protocol.  The bus is supposed to be run at no more
than 400khz until the card identification procedure is completed.  (I
suspect most modern card can run the ID sequence at full speed.)

I wonder if the real problem is a violation of a rule about switching
speed after the ID sequence... I vaguely remember there are some rules
about that, like after sending commands that change the bus config you
have to wait a certain number of cycles for the card to adjust.

-- Ian