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@dplanet.ch To: "Ronald G Minnich" rminnich@lanl.gov; linuxbios@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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