Re: RFC: outb 0x80 in inb_p, outb_p harmful on some modern AMD64 with MCP51 laptops

Rene Herman
2007-12-10T12:10:01Z

On 10-12-07 12:30, Krzysztof Halasa wrote:

> Rene Herman <rene.herman@keyaccess.nl> writes:
>
>> Alan, did you double-check that 8 us? I tried to but I seem to not
>> have trustworthy documentation.
>
> I remember 16-bit CPU-driven ISA was able to do 2-3 MB/s transfers,
> that means at least 1 Maccesses/second = up to 1 microsecond/access.

Yes, the thing is that I'm fairly convinced that an out to an unused port
takes sort of exactly 1 us (8 cycles at 8 MHz). That's what I've always
known it to be at least and have taken as the point. The same's also said
here for example:

http://tldp.org/HOWTO/IO-Port-Programming-4.html

as well as in the bit of MINIX source in an earlier version of this thread:

http://lkml.org/lkml/2002/3/14/194

Oh, in fact, a few older posts by Alan himself:

http://lkml.org/lkml/2002/3/15/2
http://lkml.org/lkml/2003/9/22/263

I'm not a hardware person as the level of actual electrical signals but if
an earlier instance of Alan is disagreeing with the current one as well, I
guess it's halfway safe to join that one...

Rene.