Date: Sat, 7 Oct 95 01:30 WET DST From: uhclem%nemesis@fw.ast.com To: FreeBSD-gnats-submit@freebsd.org Subject: kern/770: Floppy kernel won't boot with T485 or IDT L2 cache FDIV032 Message-ID: <m0t1SmU-000IsgC@nemesis.lonestar.org> Resent-Message-ID: <199510070640.XAA13079@freefall.freebsd.org>
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>Number: 770
>Category: kern
>Synopsis: Floppy kernel won't boot with T485 or IDT L2 cache FDIV032
>Confidential: no
>Severity: serious
>Priority: high
>Responsible: freebsd-bugs
>State: open
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Fri Oct 6 23:40:00 PDT 1995
>Last-Modified:
>Originator: Frank Durda IV
>Organization:
>Release: FreeBSD 2.1.0-951005-SNAP
>Environment:
Stock 2.1.0-951005-SNAP system.
>Description:
When booting the FreeBSD 2.1.0-951005-SNAP boot.flp on a 486SX or
486DX-based system that uses a Intel 485-T Turbo Cache(TM) Module, or the
IDT clone (both are L2 caches), the system hangs and will not display the
Copyright message.
As above, but if you remove the cache module (some models have this
module socketed), the floppy boot will succeed and installation is
possible.
Once the system is installed on the hard disk, the L2 cache module may be
reinstalled and the system will continue to work.
The problem only appears when booting a compressed kernel.
Operation appears to be normal when running from the hard disk.
>How-To-Repeat:
On one of the systems in questions (GRiD 486ei, DEC 1027, Tandy 4833T/C,
and a Victor model using the same MLB), insert a floppy containing
boot.flp and attempt to boot system. You will see:
...messages skipped
BIOS Basemem (639K) != RTC (basemem 640K)
and then the system hangs instead of displaying:
Copyright (C) 1982, 1986, ...
Turn off power and on the models that allow the cache to be unplugged
(DEC 1027), and do so. Now reboot with the floppy and the installation
will be successful. Once the system is installed on the hard disk,
turn system off and re-install cache.
On the systems where the T485 cannot be removed, you are stuck.
This is a transparent cache system, and there is no BIOS initialization
of this L2 cache. It was designed to be automatic. The CPU can
disable it only by disabling its internal cache as well.
This problem appeared in 2.0.5-ALPHA (the previous SNAP042x and earlier
worked fine) and persists today.
The IDT cache module (a 100% plug-in replacement) fails in the same way.
FYI, the Intel databook says the 485T cache is not a split I/D cache.
The 485-T was known early in its Intel life as a "C-6". They come in
64K and 128K sizes. The failure occurs on systems with either size.
>Fix:
None known, although an uncompressed, two-floppy boot would probably
work. Alternatively, install system by putting your hard disk in a
friends computer with a different cache design (or no cache) and
once the installation is done, bring the HD back over to your 485-T
based system.
>Audit-Trail:
>Unformatted:
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