[coreboot] your preferred method for supplying power to chip for RPi spi flashing?
michael at qubes-os.org
Fri Dec 16 13:35:00 CET 2016
Peter Stuge wrote:
> Michael Carbone wrote:
>> I have been attempting to use a raspberry pi for spi flashing and when I
>> use the 3.3v pin the raspberry pi doesn't power up as the chip draws too
>> much power through the 3.3v pin for the raspberry pi to also run.
> It's not the flash chip drawing current, it's the rest of the mainboard.
> A PC mainboard has 10-20 different voltages. The 3.3 V rail with the
> flash chip is only one of them. Each platform (CPU+chipset) defines a
> strict sequence and timing for turning voltages on, for the platform
> to function correctly.
> If the mainboard is otherwise unpowered and the 3.3 V rail is connected
> to an external supply then that sequence and the timing is guaranteed to
> be violated. This could cause anything from permanent hardware damage
> (maybe unlikely, but certainly possible) to random malfunction, e.g.
> excessive current draw, as long as the outside supply is connected.
>> What is your recommended method for powering the chip and RPi?
>> Looking online  some folks recommend using laptop AC adapter +
>> wake-on-lan (and not using the VCC/3.3v pin), but I'm not sure
>> that's a dependable strategy
> In fact I consider it the *only* dependable strategy. It is the
> obvious way to adhere to the required power up sequence.
Thanks everyone for sharing their advice on this -- I can confirm that
the Wake-on-LAN method works.
If you are interested I have documented the full process of flashing an
x230 with Heads:
Qubes OS | https://www.qubes-os.org
PGP fingerprint: D3D8 BEBF ECE8 91AC 46A7 30DE 63FC 4D26 84A7 33B4
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