Cc: Alan Cox <alan@...>, Rene Herman <rene.herman@...>, Paul Rolland <rol@...>, David Newall <david@...>, H. Peter Anvin <hpa@...>, Krzysztof Halasa <khc@...>, Pavel Machek <pavel@...>, Andi Kleen <andi@...>, <linux-kernel@...>, Thomas Gleixner <tglx@...>, Ingo Molnar <mingo@...>, <rol@...>
Hmmm,
I didn't know you worked in Boca Raton for Don Estrage on
the IBM 5150. I must have missed you --somehow.
[Snipped...]
You do remember that the X86 can do back-to-back port
instructions faster than the ISA bus capacity can be
charged, don't you? You do remember the admonishment
about:
intel asm
mov dx, port ; One of two adjacent ports
mov al,ffh ; All bits set
out dx,al ; Output to port, bits start charging bus
inc al ; Al becomes 0
inc dx ; Next port
out dx,al ; Write 0 there, data bits discharged
When the port at 'port' gets its data, it will likely
be 0, not 0xff, because the intervening instructions
can execute faster than a heavily-loaded ISA bus.
So, with a true ISA/EISA bus, not an emulated one off
a bridge, you have to worry about this. In the IBM/PC
BIOS listing, supplied with every early real PC, it
was called "bus settle time." Remember? If not, you
never wrote code for that platform.
Cheers,
Dick Johnson
Penguin : Linux version 2.6.22.1 on an i686 machine (5588.29 BogoMips).
My book : http://www.AbominableFirebug.com/
_
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