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Friday, August 11, 2006

An MMU? Cool

[Notes from another ECD hacker]

> ECD Micromind ... based on the 6502 processor, but
> had minicomputer features including:
> a 64M address space [the stock 6502 could only address 64k],
Only 64k virtual at a time. There was an MMU to remap it onto a
larger physical memory, but few, if any Microminds ever had more than
64k including video memory.

> a supervisor mode, and (possibly)

Don't think so.

> additional opcodes  (which the CPU board kept away from the 6502
> processor).

It had an illegal opcode ROM table that triggered a non-maskable
interrupt upon fetch of an illegal opcode. The 6502 was notorious for
doing unreasonably strange things when fed nonsense code...