XO-1 SD card access during boot-up

Sascha Silbe 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 [2] 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 [1], if the SD card
containing the image to be flashed indeed gets powered down
intermittently during flashing.


[1] message-id:toeobphnrh2.fsf at twin.sascha.silbe.org
[2] https://www.sdcard.org/downloads/pls/simplified_specs/Part_1_Physical_Layer_Simplified_Specification_Ver_3.01_Final_100518.pdf
    Figure 4-1, PDF page 32
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