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Re: some questions
Kim asks,
> 1) state machine of PCI revision 2.0 p175 :
>
> B_BUSY
> goto B_BUSY if(!FRAME# +...)
> goto IDLE if FRAME#
> goto S_DATA if (!FRAME# + !IRDY#)*...
> ^^^^^^^^^^^^^^^^^
>
> are those gotos arranged in descending priority ?
> Because then I'm wondering about the third goto.
>
> In case FRAME=true, then state= IDLE,
> In case FRAME=not true, then check the third goto (if the first goto is
> false of course)
> So the line (!FRAME# + !IRDY#) will in that case always be true.
>
> Why did they put !IRDY# in that line then (if the gotos are in
> descending priority) ?
The equations are in NO priority. They have enough terms in them such that
one and only one of the if ... statements will evaluate to true at any
given
time. The if-then-else-if-then-else-if-then-else... type constructs of
HDLs
that imply a priority are there to make life easy on the humans.
>
> 2) When, at power up, the BIOS assigns a base address to the device...
> how does the BIOS know no parity error has occured ?
> Because the PERR enable bit must be set by the device driver, but
> the device driver is only executed after boot up.
>
> Or does a configuration transaction doesn't need parity error checking
> ?
If the BIOS wanted to check for parity errors without enabling PERR#
assertion,
it could read bit 15 of the device status configuration register. This bit
will go active whenever a device detects a parity error, regardless of
whether
or not PERR# assertion is enabled. See page 157 of the 2.0 spec...
> 3) I still don't quite understand how to assign the exact amount of
> memory and IO space a device needs.
>
> For my device, I connect a stc101(a link switch) to my PCI interface
> (xilinx fpga).
> The stc101 has an address range from address[4:0]
>
> For my IO base address I choosed ba[31:8] (the maximum,256 bytes)
> For my mem base address I choosed ba[31:16]
>
> Of course, these BA aren't the exact amount my device needs.
>
> Would the correct IO base address be BA[31:6] ? (respecting the
> the stc address[4:0] and reserved address1 and IO indecator address0)
If the thing that you're connecting only has 5 address bits (4:0), then you
only need to request 32 bytes. Whether you want those 32 bytes to be in
I/O
space or memory space determines what you should ask for.
> And how do I determine the exact amount the MEM base address needs ?
If you don't need any memory space, then don't ask for any.
> Thanks for your time and reading,
>
> Kim
>
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