[coreboot] Tester devices [was: QA contribution]

[Juhana Helovuo]

Peter Stuge wrote:
> Juhana Helovuo wrote:
>> Here are some images of my first (incomplete) prototype:
>>
>> http://alpskari.asiantuntijat.org/~juhe/spi-flasher-piirilevyt/
> 
> Looks like a great start!

Now there is more progress. After some building, coding, and debugging I 
have the tester sort-of-working.

The first version of the hardware works.

In this image you can see the tester plugged into an Asus mainboard:

http://alpskari.asiantuntijat.org/~juhe/in-system-flasher/DSC08430.jpg

Today I successfully used this setup to reflash the mainboard from the 
host PC via flashrom.

The USB cable goes to a host computer, which is running a modified 
flashrom program. The flashrom is extended with a serprog_spi module, 
which can transfer SPI over the serprog protocol, and additionally 
toggle SPI bus multiplexer between the MCU and mainboard at the 
beginning and end of programming.

Target reset switch is still operated manually, but there is hardware 
support for operating also that from the tester board. Reset pins on the 
mainboard need to be connected to pin header in the corner of the bigger 
PCB, and flashrom needs to be extended to send also the reset command to 
the tester. The ATX power button can be operated in the same fashion.


The tester hardware has the following features:

* Single USB connection to host PC, tester is USB powered.
* RS-232 serial port to collect boot log from the target mainboard. 
Tested to work at 115200 bps.
* Two software-controllable switches for controlling mainboard 
pushbutton inputs. Button-sensing voltage on mainboard need not be the 
same as Vcc on tester.
* Small PCB mounted to mainboard can be powered by tester PCB or mainboard.
* Mainboard can operate normally even when tester has no power.
* Tester can access the ROM also when disconnected from the target 
mainboard.
* Two software-controllable LEDs to impress people.



The work is still quite incomplete:

* The first PCB had two layout errors (corrected by jumper wires), so it 
needs some rework.

* Some host-side software is missing. Flashrom extension or a separate 
program is needed to control the pushbutton inputs.

* The PCB could be extended to include a software-controlled isolated 
switch to control a relay, which can switch mains power of the target 
mainboard on or off. I am still uncertain whether I want to have 
self-hacked devices with 230 VAC parts in my house.

* Currently there is no tester firmware that could operate both the SPI 
and RS-232. The main problem is that the AT90USB162 microcontroller 
supports only up to five USB endpoints (including default control EP). I 
do not know if it is possible to implement two USB CDC class virtual 
serial ports with less than seven EPs. With two serial ports, one could 
represent the RS-232 interface, and other be used to control the 
programmer without writing any custom USB drivers.

This could be solved either in software by writing a custom USB driver 
for both the tester and the host, or in hardware by replacing the 
microcontroller with a more capable model. If anyone on the list can 
suggest any easier solutions, I'd be glad to hear about them.

* The handling of SPI ROM is horribly slow. Programming and verifying 1 
MByte ROM takes about half an hour. The main suspect is nonexistent USB 
data buffering in the tester firmware.


Best regards,
Juhana Helovuo