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From: bayes@hpislx.HP.COM (Scott Bayes)
Newsgroups: comp.sys.mac.misc
Subject: Re: ROM in RAM
Message-ID: <13740004@hpislx.HP.COM>
Date: 5 Nov 90 17:15:43 GMT
References: <1990Oct31.032509.265@bushido.uucp>
Organization: Measurement Systems Operation - Loveland, CO
Lines: 10

To map RAM into ROM addresses doesn't require a PMMU.  As long as your
accelerator card (and the internal Mac bus) has the capability to
disable the ROM and the ability to make the RAM segment respond to
addressing at the ROM addresses, it's easy.  If you can drive the "chip
enable/disable" line to the ROMs, part one is solved, and part 2 is
easy, if you use a soft-loadable address decoder on the accelerator
board RAM.  This should solve all come-from problems, etc, rather
cheaply.

Scott "not really a H/W hack, but seen it before" Bayes