Wilder than you think. Some serious research shows that
access to IDs 0 - 2, (3?), is restricted or not possible due to
the conflicting nature of how it works. I have done some
basic disassembling of the video bios and boot bios but not
found the area yet that detects at least ID0 at 0, zero, TTL
As for the USB idea, I daren`t even think about "VCC loading"
as my projects are aimed at 10 year olds to build for themselves.
Anything that is likely to cause serious damage to the computer
is a No No...
This is for MikeOS and if you haven`t tried it yet it has some
serious limitations. This is why I`m getting into it with some
of my projects ported to it and thoroughly enjoying it.
1) The whole OS runs in one 16 bit SEGMENT ONLY.
(Not strictly true but close enough... :)
2) All of the OS relies entirely on legacy BIOS routines.
3) There is ONLY 32KB of memory to code in and that can be
MIKE-BASIC and/or assembly code.
4) The BASIC interpreter, IS BASIC, by any other name.
5) ONLY COM1/ttyS0 is available at boot in two baud rates.
(The parallel port is available in SPP mode only.)
6) USB boot IS possible as this is a function of INT 19; this
is an extension that is transparent to the user. I use a USB
floppy on this notebook for MikeOS.
7) AFAIK legacy USB is for USB 1.0 only, but I could be wrong
nowadays as it was some years ago when I reasearched it.
This means KB, (and Mouse???) ONLY; so therefore no serial
ports... Nice try though... :)
8) All I/O, (note:- NOT video DMA), is inside the standard base
memory 0 - 2, (-4?) KB as is normal. From this fact I am
wondering if I/O address 220h is available for legacy sound
access. It is never shown on serious current OSs as it is not
required but I may be able to enable a sound card at
assembly level to use the "recorder", (Mic), input and use it
as a VCO input. The problem with this is ancient sound cards
used IRQ 5 or 7 to enable and we have progressed to IRQ 23
for this notebook and I`m not sure at this point in time
whether high IRQs are recognised in REAL mode.
Time for more research I guess...