Date: Wed, 28 Apr 1999 11:58:05 -0500 From: Tony Overfield <tony@dell.com> To: Nate Williams <nate@mt.sri.com>, Doug Rabson <dfr@nlsystems.com> Cc: Warner Losh <imp@harmony.village.org>, Nate Williams <nate@mt.sri.com>, Alex Zepeda <garbanzo@hooked.net>, Peter Mutsaers <plm@xs4all.nl>, freebsd-current@FreeBSD.ORG Subject: RTC extmem - was: Re: suspend mode broken since one week ago Message-ID: <3.0.6.32.19990428115805.03c08a50@bug.us.dell.com> In-Reply-To: <199904281414.IAA08646@mt.sri.com> References: <Pine.BSF.4.05.9904280904070.36113-100000@herring.nlsystems.com> <199904280422.WAA04592@harmony.village.org> <Pine.BSF.4.05.9904280904070.36113-100000@herring.nlsystems.com>
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>>[regarding RTC vs. BIOS selection algorithm]
>I don't think this is complete, because I think (don't know) that many
>older BIOS's only reported up to 64M of memory, so if you had more than
>64M in the box it didn't report it.
The RTC extmem cannot "report" >64 MB either. In fact, the RTC extmem
is unreliable for many >64 MB systems.
The only time reading the RTC extmem was helpful was when the BIOS
reported less than 64 MB and the RTC extmem "reported" more than the
BIOS, but still less than or equal to 64 MB. The exception to this
is the case where the BIOS is trying to hide something from the
operating system, such as the ACPI tables. Again, using the BIOS
value is the right choice.
Reading the RTC extmem value is only useful for systems that meet
all of these requirements:
1. They do not support either of the newer BIOS memory functions,
int 0x15 - 0xe820 or 0xe801.
2. They have an int 0x15 - 0x8800 function that is artificially
limited to a value below 64 MB.
3. They do not have a BIOS that is trying to hide something
important from the operating system.
The number of systems for which this happens is becoming vanishingly
small, IMO. (Yes, I do know which ones they were.)
Tony
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