XO-1 SD card access during boot-up
silbe at activitycentral.com
Tue May 29 18:08:40 EDT 2012
James Cameron <quozl at laptop.org> writes:
> The XO-1 SD card slot power supply circuit does not have a discharge
> clamping function, and so when the firmware or software turns off the
> power to the slot, the voltage falls slowly.
> The fall rate violates the specification for cards.
> When an SD card is used as the boot media, it remains powered, and so
> one would typically not see this symptom.
I understand this is only once Linux has taken over; OFW always powers
down the card after each access?
> Open Firmware briefly powers the SD card slot during boot, as part of
> the search for an operating system to boot.
Would it be possible to avoid powering down the card after the first
power-up in OFW? Or is a "software reset" (i.e. CMD0) insufficient for
reinitialisation in Linux? (The standard suggests  it is, but actual
cards may or may not be behave that way.)
Would something like
' noop to card-power-off
be sufficient or does OFW rely on the card getting powered down?
I may have hit this problem again recently , if the SD card
containing the image to be flashed indeed gets powered down
intermittently during flashing.
 message-id:toeobphnrh2.fsf at twin.sascha.silbe.org
Figure 4-1, PDF page 32
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