On Fri, 30 Apr 1999 12:22:17 +0200, Stephan M�ller wrote:
>With these 2 things you can connect a flash/eprom/prom/whatever to a
>specific
>location in the system-memory (first 16meg, i think on isa-bus)
Ah! Very much like video memory or adapter RAM... **NOW** I understand the
ISA bus speeed question and why it was important!!
Tim Massey
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On Fri, 30 Apr 1999 04:03:52 -0230, James Oakley wrote:
>"Timothy J. Massey" wrote:
>
>> Isn't the ISA bus usually limited to 8MHz? I've seen ISA busses overclocked
>> as high as 16MHz, but never any higher. So, a 20MHz scope should show you
>> how fast the CPU is accessing the BIOS.
>
>You're right. I was wondering how fast the BIOS was accessed, ISA speed
>or something closer to memory speed (I think it's ISA speed, but I'll
>check anyway). If it's ISA speed, the board will be much simpler as we
>can just wire the signals from the ISA bus.
After I reread your message, I figured that was what you were asking. But
here's my question, I guess: what do you mean, "We can just wire the
signals from the ISA bus." How can you just pick what signal wires you use?
If the BIOS needs line x, you need to give it x! And if the BIOS signal
wires are already using ISA bus signal lines, then why would you have had a
question about how fast the CPU access the BIOS? In that case, the access
speed to the BIOS would *have* to be ISA bus speeds!
Of course, my understanding is not relevant to the working of your circuit.
If you don't feel like wasting your time on my understanding, I would
understand. ;)
Tim Massey
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the address decode for your BIOS is not so simple. Many many motherboards
support shadowing your ROM into the much faster RAM for access. Also
sometimes the CS/ doesn't come from the address bus of the ISA bus at all,
but rather the internal address bus of the chipset. The CS/ may be derived
from a CSBIOS/ pin from some chipset IC and if CSBIOS/ is active the
external bus may not even be driven! If you are relying the address to
appear on the ISA bus you may be in for a surprise.
I like the idea of cutting the CS/ pin and wiring up some small logic:
CS(old) = CS(mb) AND BIOS_SEL
CS(new) = CS(mb) AND /BIOS_SEL
where CS(old) = the CS/ pin on the orignal BIOS
CS(new) = the CS/ pin on the new BIOS
CS(mb) = the original CS/ signal from the motherboard.
This can be done cheaply with a few HC or F series gates and if you're
feeling creative, pull BIIOS_SEL up to VCC and use the turbo switch to
ground the input to select which one to use. The ICs will be happy and you
won't have to worry about about long lead lengths causing ringing to the CS/
signal.
As far as mounting the new ROM -- why not just take a wirewrap socket, cut
the CS/ pin short and solder the remainder of the pins directly ON TOP (i.e.
in parallel) with the original ROM? (minus the CS/ of course...) Then wire
up the CS signals as shown above.
whichever ROM is selected will follow the proper "rules" as far as the
motherboard is concerned. they will follow shadowing and cacheing too, so
long as you don't switch which BIOS is active while the computer is on all
should be fine.
In addition, if you get tired of the project, you can remove the new BIOS,
leave the socket on there but permanently activate the original BIOS and the
computer is no worse for wear.
back to lurker mode,
Andrew
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Niklas Ekström wrote:
> How do you plan on disabling the onboard FlashBIOS chip?
That's the easy part: remove it. However, there are some boards out
there that use those damn SMT flashes. For development, it's probably a
good idea to stay away from these boards.
All of the signals in the socket save one are on the ISA bus. The other
signal, which controls the CE line on the flash will be run to the
switch, which will switch it between the two flashes on the board.
One thing I have to find out however, is how fast the processor accesses
the BIOS. I'll have to hook it up to my scope (though I may not learn
much from that as it's only a 20MHz scope) and see if I can grab the
frequency. Actually, I'm going back to school next week (this is my 2nd
last day of work, ahhh) and we have 100MHz digital HP scopes in the
digital labs (you can play Tetris on them!) I can play with.
I'll have to try that this weekend, and try the circuit out on an ISA
prototype card.
james oakley
jfunk(a)roadrnner.nf.net
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On Fri, 30 Apr 1999 01:05:25 -0230, James Oakley wrote:
>One thing I have to find out however, is how fast the processor accesses
>the BIOS. I'll have to hook it up to my scope (though I may not learn
>much from that as it's only a 20MHz scope)
I could be wrong but...
Isn't the ISA bus usually limited to 8MHz? I've seen ISA busses overclocked
as high as 16MHz, but never any higher. So, a 20MHz scope should show you
how fast the CPU is accessing the BIOS.
Of course, It's been a few years since my Digital Electronics classes...
Tim Massey
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On Thu, 29 Apr 1999 12:39:27 -0230, James Oakley wrote:
>GPIO - General purpose I/O. This is for the hardware people (like me)
>who have run out of parallel ports and want to make your PC control neat
>stuff.
That's me too! I don't have the time or the skills necessary to program a
BIOS, but controlling neat stuff: yeah!
What will the cost of one of these little boards cost?
Tim Massey
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"Timothy J. Massey" wrote:
> I am absolutely brand new to the list, and I'm trying to figure out what's
> going on. The project sounds very exciting!
>
> I'm curious, though: A PCB? What for?
Ah, since there's no web page describing it yet (when it's done one will
be put up, hopefully next week) I'll explain it briefly.
It performs three functions:
POST - For debugging purposes, it will display POST codes from port 80.
However, there will be a header for a character LCD module to display
human readable bootup messages on a different port. It can also be used
by the operating system to display statistical information (ala LCDProc
for Linux), useful for servers, etc which have no monitors.
Flash switch - Will switch between a backup flash and a test flash so
that you won't need to burn code using a ROM programmer and physically
insert them into the motherboard (or risk blindly programming one BIOS).
You switch between them using a switch on front of the PC (in a 5-1/4
slot, next to the LCD if you have one, I'm sure everyone has empty
ones). The backup BIOS is wired so that it cannot be written to (this
has the useful side effect of making your PC immune to flash virii).
This allows for a really quick development cycle (yay!) and anyone
seriously working on OpenBIOS will really benefit from this.
GPIO - General purpose I/O. This is for the hardware people (like me)
who have run out of parallel ports and want to make your PC control neat
stuff. This also makes it great for the embedded people (like me) who
want to make systems without requiring unnecessary hardware (video
card). You can even use the test flash for your "target" system and the
backup flash for your "development" system. This can control relays,
A/D, D/A, etc, important if you do the kind of stuff I've been doing
(industrial process control, I hate PLCs). It's great for students
learning hardware programming as well.
I'll try to finish it up this weekend, one thing I'm wondering about
though. How fast does the processor try to read the BIOS? We may be able
to get away with putting most of the flash lines on the ISA bus, only
needing one wire into the socket. Will this work? I'll make a board and
try it out anyway unless someone tells me otherwise.
james oakley
jfunk(a)roadrunner.nf.net
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"Darran D. Rimron" wrote:
> > Ping ? ;)
>
> "It was so quiet, you could hear a pin drop...."
Yeah, it's been pretty quiet. I now will finally have some time to
actually do stuff now when my workterm ends on friday. I have a PCB
etching tank being made, it should be ready on Monday (I'll be making
boards for my current employer). I also now have a contact at the local
university PCB shop who can do double sided, tin-plated, through-hole
boards for me for cheap. I'll buckle down this weekend and get a final
schematic/PCB on to the list to see if it's what everybody wants. If so,
I'll make one.
james oakley
jfunk(a)roadrunner.nf.net
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