sd card probing (was: FreeBSD 10.0 on Raspberry PI B+ no network devices

[Ian Lepore]

On Wed, 2014-10-29 at 14:59 -0600, Warner Losh wrote:
> On Oct 29, 2014, at 2:16 PM, Ian Lepore <ian at FreeBSD.org> wrote:
> 
> > On Wed, 2014-10-29 at 21:04 +0100, Bernd Walter wrote:
> >> On Wed, Oct 29, 2014 at 11:58:21AM -0600, Ian Lepore wrote:
> >>> On Wed, 2014-10-29 at 18:29 +0100, Bernd Walter wrote:
> >>>> On Thu, Oct 23, 2014 at 04:22:44AM +0200, Bernd Walter wrote:
> >>>>> On Wed, Oct 22, 2014 at 11:43:01PM -0200, Luiz Otavio O Souza wrote:
> >>>>>> On 22 October 2014 18:44, Bernd Walter  wrote:
> >>>>>>> On Tue, Oct 14, 2014 at 12:51:50PM -0300, Luiz Otavio O Souza wrote:
> >>>>>>>> On 14 October 2014 01:13, Bernd Walter wrote:

[...]

> >>> 
> >>> Pullups on sd signal lines is a recent thing.  It's in the sd 4.x
> >>> physical spec, in the form of requiring the standard sd data lines be
> >>> pulled high or low when using the new UHS-II signals.  Other than that
> >>> pullups are not required on any of the lines for sd cards.  At work we
> >>> don't put pullups on any of them, and use a 22 ohm series on just the
> >>> clock line, and that only on designs where we have to fly across a
> >>> ribbon cable to get to the card socket.
> >> 
> >> Can't say since when it is in the SD spec, saw it in the MMC, but don't
> >> know how long it is there either.
> >> Anyway - I remember them well, because I had to hand wire them on my
> >> RM9200 prototype boards.
> >> It never had been a problem until Warner added higher speed support, but
> >> I don't have series resistors on my boards.
> 
> High speed on the RM9200 boards was always a bit dodgy anyway. :( Sorry for the hassle.
> 

Actually high-speed works fine by itself, it's the combo of high-speed
and 4-wire that's problematic, because of dma overruns.  It's especially
bad when usb is also active, because it gets priority on the bus.  If
the mci dma doesn't get a bus-grant in time, it's not smart enough to
stop the clock to the card, and it just looses data instead.  All in
all, the max reliable data rate is around 3 MB/sec when usb is enabled.

-- Ian