XO-1 SD card access during boot-up

James Cameron quozl at laptop.org
Wed May 30 03:42:41 EDT 2012

On Wed, May 30, 2012 at 03:14:49AM -0400, John Watlington wrote:
> On May 30, 2012, at 2:04 AM, James Cameron wrote:
> > On Wed, May 30, 2012 at 12:08:40AM +0200, Sascha Silbe wrote:
> >> Or is a "software reset" (i.e. CMD0) insufficient for
> >> reinitialisation in Linux? (The standard suggests [2] it is, but actual
> >> cards may or may not be behave that way.)
> > 
> > I don't know.  Let me know if you test it.  We know that a power cycle
> > will reset a card.
> Probably not.  If a card suffers a "brownout", which is what is happening here,
> all bets are off.   You have to power cycle the card (leaving it powered off
> long enough to ensure the supply voltage drops close to zero) to ensure proper
> operation.

Agreed.  I meant a proper power cycle, not the type provided by XO-1
without supply discharge.  My point is that it is hard to know if
leaving the power on and using CMD0 is any better than turning the
power off.  We already have a delay in the firmware to provide 250ms
fall time for XO-1 and XO-1.5.  We could increase that, but it will
slow booting still further.

James Cameron

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