Subject: fix for problem w/ NetBSD on ThinkPad 750
To: None <port-i386@NetBSD.ORG>
From: Keith Moore <>
List: port-i386
Date: 03/14/1995 18:11:55
It turns out that the BIOS on a ThinkPad 750 (as well as some other
ThinkPad models -- not sure which ones), uses the upper 4K of
conventional memory for a scratch area.  Go figure.

Anyway, for NetBSD to function properly on that machine, it needs to
be told not to use that chunk of memory.

The symptom I've seen is that the system gets wedged and nothing but a
power cycle will fix it.

The enclosed patch solved the problem.  (Thanks to MORIYAMA Takao of
IBM Japan who sent me his TP750 patches for FreeBSD.)

I'm not sure if it's worth making any changes to the official source,
because I don't really know if this is just a quirk of ThinkPads or if
other laptops that have APM, etc., have similar problems.

Keith Moore

*** machdep.c.ORIG      Fri Oct 14 10:11:44 1994
--- machdep.c   Mon Mar 13 22:16:34 1995
*** 1162,1167 ****
--- 1162,1170 ----
                    biosbasemem, BIOS_BASEMEM);
                biosbasemem = BIOS_BASEMEM;
+ #ifdef TP750
+       biosbasemem -= 4;
+ #endif
        avail_start = NBPG;     /* BIOS leaves data in low memory */
                                /* and VM system doesn't work with phys 0 */