Re: Black box flight recorder for Linux

linux-os (Dick Johnson)
2006-04-10T20:07:53Z

On Mon, 10 Apr 2006, Krzysztof Halasa wrote:

> "linux-os \(Dick Johnson\)" <linux-os@analogic.com> writes:
>
>> Further, in a boot where the BIOS needs to initialize hardware,
>> It will write all RAM before enabling NMI. This makes sure that
>> the parity bit(s) are set properly. Most BIOS will attempt to
>> preserve RAM on a 'warm' boot as a throw-back to the '286 days
>> with their above-1MB-memory-manager paged RAM because the
>> only way to get back from protected mode to 16-bit real mode
>> was a hardware reset.
>
> I think there is no distinction WRT RAM test between cold and warm
> boot anymore. If the BIOS clears the RAM is, I think, determined by
> the "fast POST" option in BIOS setup (it always checks the size
> so some bytes will be changed anyway).
>
>> When using a memory-manager like DOS's
>> HIMEM.SYS, you might actually be rebooting the machine hundreds
>> of times per second!
>
> Yes but it uses (or, rather, used) a CMOS flag to skip POST (not only
> the RAM test) and to go directly to the entry point in real mode.
>
> IIRC (I may be wrong, that was 15+ years ago) only 286 required
> KBC reset to return to real mode (did LOADALL matter?), 386s have
> no such problem.
>
>
> BTW I understand the idea have nothing to do with actual aircraft,
> so it would be the admin rather than NTSB looking at the data(?).
> --
> Krzysztof Halasa

Yes. After I responded and after reading other responses I noted that
the idea was to review the reason for a PC crash. There are no
good places to store things that can be counted upon to remain after
a crash. Even though CMOS RAM goes to 0x7f and not all of it is
needed for BIOS setup, many/(maybe all) BIOS checksum the whole
thing with some hair-brained checksum routines so it's not a good
place to store things. Many BIOS use 128k or more, which can
be re-written in 64k pages. Certainly there is space available
...but... the BIOS would be trashed if a power-failure occurred
during the write, so that's not a good place either. I did, at
one time, use a "spare" page of screen memory (one that wasn't
displayed) during the boot process (buffering for a bootable NVRAM
disk). This is "available" RAM, but it isn't going to survive
even as screen-card reset!

Cheers,
Dick Johnson
Penguin : Linux version 2.6.15.4 on an i686 machine (5589.42 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_
\x1a\x04

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