Re: Linux Post codes during runtime, possibly OT

Brian Gerst
2001-01-26T16:34:52Z

"Richard B. Johnson" wrote:
>
> On Fri, 26 Jan 2001, Manfred Spraul wrote:
>
> > > + *
> > > + * Changed the slow-down I/O port from 0x80 to 0x19. 0x19 is a
> > > + * DMA controller scratch register. rjohnson@analogic.com
> > > */
> > >
> > What about making that a config option?
> >
> > default: delay with 'outb 0x80', other options could be
> > udelay(n); (n=1,2,3)
> > outb 0x19
> >
> > 0x80 is a safe port, and IMHO changing the port on all i386 systems
> > because it's needed for some embedded system debuggers is too dangerous.
> >
> Dangerous? udelay(1) on a 33 MHz system is like udelay(100). Don't
> get too used to 800+ MHz CPUs. There are systems, probably most in
> the world, that need 300 +/- nanosecond delays. This is what the
> port I/O does.

In most of the cases where this delay is needed, it is a _minimum_
delay. It is usually time enough for the hardware to react to an index
register being written to, etc. In most cases, a longer delay on slower
machines should not hurt.

--

Brian Gerst