[coreboot] [RFC] cheapish and free usb spi flashing device

Peter Stuge peter at stuge.se
Fri Apr 22 05:08:32 CEST 2011

Stefan Tauner wrote:
> i am currently designing a small and cheap platform to recover from
> coreboot and other failures easily.

Yay more flashers.

> right now my plan is the following:
> an avr atmegaXXu2 is connected via usb and implements the serprog
> protocol

Please do not! Make good use of USB and design a protocol that
actually takes advantage of relevant USB features, instead of
pretending that USB is a serial port, which is really lame.

At a very minimum translate the serprog protocol to native USB.

USB is a packet bus. Making it behave like a dumb stream of bytes is
almost never a good idea.

Also, make a simple HAL for the AVR, so that your C firmware can be
re-used with other processors. I'll make it run on LPC1342/43.

> easy interfacing with today's spi flashes

SPI access should also be part of the HAL of course.

> without any level shifting.

Yes, is a good feature.

> fixed 3.3V ldo voltage regulator (ld1117).

LD? LM? Anyway, that's an 800mA regulator, quite overkill for this
application where not even 100mA is required. A smaller one should be

> - vias for a single row 8pin header to allow attaching probes/test clips
>   (e.g. http://www.pomonaelectronics.com/images/large/6109.jpg) to hook
>   up in-situ flashes.

May want to consider how the test clip is connected to board. The
cables on my clips go to a DIP-style connector that plugs into an
8-pin socket.

> parts for this excluding the pcb would be in the 10-25$ range.
> depending on how many pcbs i/we would produce the whole thing would
> cost probably about 40$. not THAT cheap, but quite better than
> the dediprog stuff :)

That LPC1343 I mentioned is available on a board from Olimex which is
ready made, easy to order at least in Europe, has SPI and power
supply on a convenient box header (UEXT) and a small experiment area.


It's 13 EUR + shipping and VAT.

> it would also be more convenient and open than the FT2232SPI

Did I mention how I really think USB serial chips are stupid, and
FTDI in particular because they have ridiculous prices.

> i am not sure about what to do with soic16 chips.

I also don't think they are very common.

> drop support for them altogether and let the user hook them up with clips?

Certainly an option.

> i was also thinking about an offline mode which uses an SD-card or
> another flash to store/load an image for the target flash.

SD is not worth the effort. SD cards are very incompatible and it
takes a lot of work to implement a well-functioning card reader. And
the filesystems are buggy as well.

A second flash chip could be handy for offline mode - but what is
supplying the power?


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