your preferred method for supplying power to chip for RPi spi flashing?

[Michael Carbone]

Hi coreboot list,

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. I am
powering the RPi through micro-USB, either connected to wall outlet or
another computer.

What is your recommended method for powering the chip and RPi?

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 because I don't know if coreboot has WoL
functionality for the x230 should I want to reflash the chip [2].

Advice/thoughts appreciated, and let me know if there's a better place
to ask this question.

FYI this is the chip I am trying to program: [3]

Thanks,
Michael

[1]
https://www.bios-mods.com/forum/Thread-REQUEST-Lenovo-Thinkpad-X230-Whitelis...
[2] https://www.coreboot.org/Board:lenovo/x230
[3] http://www.zlgmcu.com/mxic/pdf/NOR_Flash_c/MX25L3206E_DS_EN.pdf

-- 
Michael Carbone

Qubes OS | https://www.qubes-os.org
@QubesOS <https://www.twitter.com/QubesOS>

PGP fingerprint: D3D8 BEBF ECE8 91AC 46A7 30DE 63FC 4D26 84A7 33B4

[Peter Stuge]

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 [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.

The next question becomes - how to ensure that the SPI bus master is
not driving the SPI bus, when the mainboard is powered?

This requires some platform- and possibly mainboard-specific research
into exactly how the SPI master powers up.

On i945 platforms (X60, T60), the 3.3 V rail is active whenever the AC
adapter is connected, also when the system is off. Very handy. On
other platforms that's not neccessarily the case, and some tricks can
and will be needed to get 3.3 V up but keep the SPI master in reset,
hoping that will make its SPI output pins high-impedance, rather than
drive 0 or 1. The latter would cause a short circuit if the external
SPI programmer drives the opposite level.


The correct solution to having two SPI masters with a single slave
(flash chip) is to insert a bus switch before the slave, so that only
one master can access the flash at any given time. This requires
moving the flash chip off the mainboard onto an adapter PCB with the
bus switch on it. There exists an open design for such an adapter PCB
already, but I don't know off the top of my head who made it.
Hopefully the author or someone else (lynxis?) can post the link.


Thanks

//Peter

[Trammell Hudson]

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

[Zoran Stojsavljevic]

> Now I always unplug the AC adapter and remove the battery before
> powering up my flasher (although I do leave the chip-clip connected).

This is about right. I programmed most of INTEL platforms using dediprog
SF100: ATOM: from D4xx/D5xx (Pine Creek) series, TNC, BYT-M/I, BSW and CORE
(IVB, HSW, BDX-DE, BDW-H, SKL-Y/U), whereas for some HSW-U series it was
necessary to put platform in S5 state by shutting down them to S5. AC in
most cases removed, I did not have battery since I played with test
platforms. And there were 4x2 pins connectors for most of platforms,
recently with special small connector forms and adapters for SF100
programming heads, but in some cases I needed clip to connect directly to
flash.

Zoran

On Thu, Dec 1, 2016 at 3:02 PM, Trammell Hudson <[e-mail]> wrote:
> 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?