The DoC problem
Bari Ari
bari at onelabs.com
Tue Sep 10 13:56:01 CEST 2002
A flash adapter of this type is only economical is high volume. The BOM
and assembly costs in low volumes are higher than the cost of a off the
shelf motherboard unless you plan on building them yourself and your
time is of no or little value.
A design to page out flash memory into a small space in memory is done
the way Expanded Memory was done for the old IBM-PC via page frames.
Here's an example of how it could map into system memory:
PC MAIN MEMORY LIM EXPANDED MEMORY -------------- -------------------
+-------------+ | | . Extended . . Memory . . up to . /+-------------+
32M . 16M on the . // | | . '286, . / / | | . 4096M on . / / | Expanded
| . the '386 . / / | Memory | | | / / | | 1M +-------------+ / / |
Divided | | | / / | into 16K | 960K +-------------+ / | logical | | Page
Frame | / | pages | | 12*16K | / | | | Physical | / | | | Pages | / | |
768K +-------------+\ / . . | | / . . 640K +-------------+/ \ . . | Page
Frame | \ . . | 24*16K | \ | | | Physical | \ | | | Pages | \ | | | | \
| | 256K +-------------+ \ | | | | \ \ | | | | \ \ | | | | \ \ | | 0
+-------------+ \ \ | | \ \ | | \ \ | | \ \| | \+-------------+ 0
The example shows how expanded memory gives you up to a 32M to map into
up to 36 16K pages in the positions shown above.
If anyone wants schematics I can dig through some Orcads from the 80's
and pass em along ;)
Bari
Jan Kok wrote:
>Hamish, what would you use for a plug to plug into the BIOS socket? I
>searched all over the place for a plug (or PLCC to DIP adapter for DoC) and
>didn't find anything useful for less than about $60 small quantity -- except
>for the Bios Savior device (about $30 from www.mwave.com).
>
>- Jan
>
>----- Original Message -----
>From: "Hamish Guthrie (Mail Lists)" <hamishl at dplanet.ch>
>To: "Ronald G Minnich" <rminnich at lanl.gov>; <linuxbios at clustermatic.org>
>Sent: Monday, September 09, 2002 4:03 AM
>Subject: RE: The DoC problem
>
>
>
>
>>I think the DoC mess is here to stay, there is one potential solution if
>>people are insisting on having DoC, and that is to make up a little board
>>which plugs into a BIOS socket which has both a 256k flash device and a
>>little bit of decode logic for a DoC, as well as a DoC - if anyone is
>>interested in this approach, I could knock together a few prototypes for a
>>couple of $'s, but I have my reservations as to this being a permanent
>>long-term solution for production systems.
>>
>>Hamish
>>
>>
>
>
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