[OpenBIOS] OpenBIOS POST, flash, and IO card site.

[James Oakley]

Chris Davis wrote:

> 1. You've hooked up IO Read and IO Write - this puts the Flash in the
> IO space, not the memory space. You need MEMRead and MEMWrite

Whoops, oversight on my part. I'll have to hook up MEMR/MEMW to the
flash. I was kinda tired when I was drawing it up, IOR/IOW is used only
for the POST and GPIO. Thanks for pointing that out.


> 2. On the actual hardware that I have seen out there, segment F000h is
> not sent to the ISA bus at all. In fact, most modern chipsets have a
> totally separate data bus for the flash and other peripherals - so you
> will never see any access to your boot board. We have used both
> techniques on boards that we have designed in the past.

This is a lack of documentation problem (I'll write some, I swear).
You'll notice that the CE lines are connected to the flash switch. The
flash switch is, in turn connected to the appropriate line from the
flash socket to address the appropriate chip. That's why there is no
address decoding circuitry.


> 3. Even if you find a board that decodes F000 to the ISA bus, you will
> now have bus contention between your board and the old standard flash
> on the motherboard. Not a problem if the flash is socketed, but many
> boards (some of ours, for example) have soldered flash, making this
> non-trivial as well.

This, I have thought of. If your flash is socketed, you only have to
remove it, (and you can put it on the new board directly, so you only
have to buy one and you don't need an EPROM programmer to put a backup
BIOS on, yay). For the SMT flashes, I originally thought it would be
best to avoid them as you could probably get a MB with socketed flash
that has the chipset you're working on. However, this may not be the
case all the time (personally, I think flash should always be socketed).
If a board has SMT flash, it would be a matter of clipping the CE pin
and wiring the signal to the flash switch, if the developer were
confident enough.


> - You could build a small carrier board to plug into the flash socket
> on your motherboard which would hold 2 flash chips and some sort of
> decoder that will switch between them under software control.

That too, I have recently thought of. You could probably place two SMT
chips on a board the size of a 28-pin DIP that would plug directly into
the original socket (like those BASIC Stamps). Software control,
however, requires I/O, which has to gotten from ISA, parallel, OpenBIOS
card, etc..


> - build support for boot-block flash into OpenBIOS.

IIRC, you can only overwrite a boot-block if you haul the chip out and
use an EPROM programmer. Hmmm.. I wonder if boot-block operates the same
from all of the BIOS companies.. We could simply be compatible with
that.

Thanks for the input, it's appreciated.


James Oakley
jfunk at roadrunner.nf.net
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