Re: cvs commit: src/sys/i386/isa rc.c

["Rodney W. Grimes" <rgrimes@xxxxxxxxxxxxxxxxxx>]

> 
> rgrimes     96/03/09 10:59:02
> 
>   Modified:    sys/i386/isa  rc.c
>   Log:
>   Convert a timeout loop from 100 iterations of 15uS to 50
>   iterations of 30uS so that really fast systems stop getting
>   timeout messages from the Riscom driver.
>   
>   Reviewed by:	ache, peter@xxxxxxxx (Peter da Silva)
>   
>   Revision  Changes    Path
>   1.21      +2 -2      src/sys/i386/isa/rc.c

Note that this patch really points to a problem in DELAY(X) for X
smaller than 20.  Right now the DELAY code does an X=-20 and never
really goes into the DELAY loop.

It seems that on 133Mhz and faster Pentium systems the assumed overhead
time of 20uS is no longer valid and something needs to be done to
correct this.  This is especially true when calling short DELAY's in
a loop since that all ends up running from the internal cache.

If you spot DELAY being called in an loop some place with values of
20 or below I suggest that the code be corrected to do what I did here
or we are going to see more of these types of problems as system
speeds increase.



-- 
Rod Grimes                                      rgrimes@xxxxxxxxxxxxxxxxxx
Accurate Automation Company                 Reliable computers for FreeBSD