microcoding a PC into a PDP-11 (was: RE: Classic Computers vs. Classic Computing)

From: emanuel stiebler <emu_at_ecubics.com>
Date: Tue Sep 18 15:20:55 2001

Jonathan Engdahl wrote:
>
> The idea is to write PDP-11 microcode for the PC platform, rather running an
> "emulator" under Windows or whatever. The Pentium would be viewed as the
> micro-architecture, the PDP-11 as the real machine. It would be table driven
> and fully expanded, using the PC memory rather extravagantly. You should be
> able to emulate simple instructions at the rate of about 4~8 Pentium opcodes
> for every PDP-11 opcode. If you rely on the Pentium MMU to trap accesses to
> the I/O page, you don't have to check for non-memory accesses from within
> the CPU model. The trap routines would emulate PDP-11 I/O, mapping it onto
> the PC hardware, rather than onto file I/O as in an emulator. The Pentium
> MMU can also be used to emulate the PDP-11 MMU. Map the PDP-11 registers
> onto Pentium registers, and never save them in memory except on a trap. This
> gives you a very, very fast PDP-11, IBM 1130, or whatever. If you can figure
> out a way to cause the machine to boot this "microcode" at powerup instead
> of Microsoft Wincrash, I argue that you could legitimately call this a
> PDP-11.

OK. But, this microcode has to have an OS around. because:

- how to use the MMU ?
- you need access to serial ports ?
- disks
- tapes
- ethernet
- etc.

Or do you like to program this stuff all by yourself ?
 

Still, definitely not a Windoze, but somekind of ukernel.
Anyway, start with it, and we see one day ;-)

cheers & have fun,
emanuel
Received on Tue Sep 18 2001 - 15:20:55 BST