tbuf par faults and 4.2bsd

[Bruce Nemnich]

> From: rees at apollo.UUCP
> Subject: tbuf par errors, once more
> Date: Mon, 4-Jun-84 08:23:32 EDT
> 
> Maybe this should go in the list of most-often asked questions about Unix?
> 
> Thanks to Dennis Ritchie, Sam Leffler, Andy Tannenbaum, and all the
> other people who helped straighten this out.
> 
> The translation buffer helps translate virtual addresses to real.  A
> tbuf par err is a parity error in the translation buffer.  The original
> 4.1bsd code didn't handle these errors correctly.  There is an ECO
> from DEC that reduces the number of these errors, but Unix should still
> be able to handle them correctly.
> 
> There are some bogus versions of this fix floating around.  They have
> mc5_mcesr&0xf instead of mc5_mcesr&0xe.  Make sure you have the right one.
> 
> I have not looked at the 4.2 code to see if this fix made it in.  This code
> is for 4.1bsd.

I just looked at the 4.2bsd code, because I have been having problems with
these faults.  Sure enough, the distributed version has the bogus fix.
Here's the 4.2bsd diff on /sys/vax/machdep.c:

810c810
< 		if ((mcf->mc5_mcesr&0xf) == MC750_TBPAR) {
---
> 		if ((mcf->mc5_mcesr&0xe) == MC750_TBPAR) {
-- 
--Bruce Nemnich, Thinking Machines Corporation, Waltham, MA