On Thu, Dec 01, 2016 at 01:15:59PM +0000, 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.

For some mainboards (like the 15" 2014 Macbook Pro) I had to add a 1-10
Ohm resistor on the power lead from my flasher, which basically glitches
the rest of the mainboard, but since many SPI flash chips can run at
a slightly lower voltage it allowed me to read/write the firmware.
This is probably not the right way to do it.

> [...]
> > Looking online [1] 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.

I've never had success with this technique due to the multi-master
situation that you described.  The PCH (or ME?) on modern CPUs
seemed to always be driving the IO lines when I provided power.
Now I always unplug the AC adapter and remove the battery before
powering up my flasher (although I do leave the chip-clip
connected).

Perhaps I'm a little more YOLO with many of my test machines than
is prudent, so I don't worry too much about what other bits are being
powered up by the 3.3V rail.  On the x230 I used an external bench
supply and found that the rail needed about 110 mA to function:

https://www.flickr.com/photos/osr/28494632165/lightbox

So on my teensy 2 flasher I replaced the small SMD regulator with
a larger UA78M33 regulator in a TO-220 package that can supply 500mA:

https://www.flickr.com/photos/osr/30531707094/lightbox

My biggest problem these days is that the chipclips seem to wear out
after a few hundred applications (the pins get pushed upwards, making
the connection flaky).  Anyone have a recommendation for one that can
stand up to constant use?

-- 
Trammell

-- 
coreboot mailing list: coreboot@coreboot.org
https://www.coreboot.org/mailman/listinfo/coreboot

Reply via email to