Re: Claiming 1M when using 8K

[Alan Deikman <alan@znyx.com>]

>Well, you can't make the I/O Bar request 1MB of I/O space because
>that's illegal now.  The 2.1 spec changed things for I/O space so that
>now you can't allocate more then 256 bytes! for an I/O bar.  In 2.0
>this was just a recommendation.  (The recommendation was an excellent 
>one for PC's, but the requirement is somewhat stupid for everyone
>else, >and 2.1 should have never made it a requirement, but..... they did
>so 256 bytes is the law of the land now for I/O.)

Remember that I/O support was mostly a concession to PC's and x86
architecture to begin with.  What bulk-RAM-access (multiple Kbytes or
more) application is better served with I/O instructions as opposed 
to memory access instructions anyway?

I see more architectures these days that don't even bother to implement
an I/O space at all.  Why waste the gates on the chip for it when all
it does is add another resource category for the OS to deal with?  The
only reason I can think of is because the 4004 had it.

If I had been specifying PCI at the start I would have been tempted
to do away with I/O transactions altogether, and simply have the
CPU-to-PCI bridges deal with the translations for those CPU 
architectures that require (want) it.

--------------------------------
  Alan Deikman, ZNYX Corporation
  alan@znyx.com
3ØÆ