simple pci

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I have an old motherboard which has four pci slots. I want to use it as
one pci output port.
I would like to use pci interface as low frequency simple output.
pci can work lower than 133/4 33%Mhz for example 133/16=8.3Mhz

no interrupt required, no handshaking. there wont be any register on
target board so no device id no port no memory information.

is it possible to output data like this?

Re: simple pci

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Off the top of my head, I can't see how this would be possible.

The PCI bus has handshaking signals that are required just to get data
out onto the bus - the address is presented first and signals like
FRAME#, TRDY#, DEVSEL# etc need to be driven correctly for the data
phase of the transaction to begin.

But even before that, I can't even see how you'd get a transaction out
onto the PCI bus in the first place?!? You won't have an address space
assigned to your card so I guess you'd have to rely on unclaimed
addresses being sent to the PCI bus??? Unless you can cleverly use PCI
configuration cycles to do your I/O for you?!?

Other opinions?


Re: simple pci

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At boot time bios assign memory and i/o address to pci card. If there
is no card it won't be assigned.
But it is not necessary actually because hot-plug devices are
configured after boot time.
I wonder without any pci card installed can I send any data to pci bus.
It's name is not important configuration i/o adress data whatever it
Can I write to pci bus without any device installed ?

Another option :

I can install a any pci card into slot, it makes necessary
After some few milliseconds I write to this card but I tap  32 data
lines from pci bus to my circuit.

At low speed I think there wont be signal integrity - impedance
8.3 Mhz x 32 bit = 250 Mbit data is very usuful for me..

What do you think is it possible ?

Re: simple pci
MY motherboard has onboard vga and ethernet. when these devices are
used, is there any traffic on pci bus?
does each device respond their own i/o adres ? or is there any other
sinal whict selects target device?
is 32 bit data signal broadcasted ? can all devices see transmission?

Re: simple pci writes:
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VGA, maybe or maybe not.

Ethernet, probably yes.

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On reset, PCI devices don't respond to any memory or I/O addresses; they
only respond to accesses to configuration space.  The BIOS or operating
system configures the devices and assigns addresses.  Once this is done,
all you need to access the device is the appropriate address.

Of course, PCI protocol still requires arbitration and handshaking,
which involves the IRDY, TRDY, and other PCI signals.

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On any given bus it can be viewed as a broadcast, but you may have more
than one PCI bus.  For instance, the onboard Ethernet might be on the
same PCI bus as the expansion slots, or it might not.

Re: simple pci
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It is, but it's not "really" PCI. Here's an example using an FPGA and
Verilog: you could translate it to a CPLD or to discrete logic if you
prefer. You'll have to find out what addresses the system already
allocates to pnp PCI, and avoid those.

If you want something more "permanent" get hold of a PLX development kit
and work from there.

Paul Burke

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