On Wednesday, July 07, 1999 3:43 PM, Blaz Antonic [SMTP:[EMAIL PROTECTED]] wrote:
: > i had an idea a few weeks ago to toggle the a20 gate on a 286, and use the
: > memory from ffff:0000 to ffff:ffff for a ramdisk. this way we could use
: > 64k-1byte of memory, which would otherwise be wasted.
:
: 8086 doesn't have A20 line ?! It might actually be more useful to find
: out what would be required to switch processor into protected mode
: (286). This way we'd have 16 MB of addressable memory. If my
: understanding is correct bcc wouldn't need any modifications in order to
: produce pmode binaries, segment limits are still there, task switching
: mechanism would still work (because of same CS and DS limitations).
The pmode ideas are good, but I think you missed the point.
A normal, old-fashioned 8086 can be tricked into getting 65535 more bytes
of memory than the normal 1 megabyte. This is accomplished
by programming the keyboard controller on PC's to hold the A20 line
high and then use the 8086's real mode address wrap "feature".
I think it would be a good idea, and might even be ok to use
it in the ELKS kernel to get another 64k of memory. Of course, whenever
the tasks switch, the kernel's got to turn on and off the damned A20 gate.
Isn't PC hardware fun 8-)
Greg
