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: [email protected] https://www.coreboot.org/mailman/listinfo/coreboot
