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Subject: Re: Hopefully last dumb newbie question. From: dempson@actrix.gen.nz (David Empson) Date: Wed, Jun 24, 1998 4p42 EDT Message-id: <1db5aaj.vui26t11kvoiN@dempson.actrix.gen.nz> Mitchell Spector <spec@vax2.concordia.ca> wrote: > In article dempson@actrix.gen.nz (David Empson) writes... > > >The only slowdown on a ROM 3 would be due to the synchronization delays > >introduced by shadowing writes in locations $0800-$0BFF of bank 0 into > >bank $E0, i.e. 1 MHz writes instead of 2.8 MHz. Nothing outside that > >address range is affected. > > > >This would have a variable effect depending on what was using that area > >of memory. Applesoft BASIC programs normally run in that area, but they > >aren't written to (except while editing or being loaded). Under GS/OS, > >it would tend to be application or toolbox direct page/stack space > >(reasonably major impact). > > Hmm, perhaps it is not as trivial a glitch as I first thought. Is > it possible my ROM 3 (even with 15 MHz Zip GS accelerator) is running > slower than it should be, and has for all these years? The ZIP GS does not cache write operations, so the only speed penalty is 1 MHz vs 2.8 MHz, even on a highly accelerated machine. I doubt you'd notice much. > Is there a way I can confirm, for certain, whether Alternate > Display Mode is constantly active on my system? (perhaps by looking > up an address in memory). You could look at the contents of the shadow register ($C035). Bit 5 is zero if text page 2 shadowing is enabled (on the 1MB/ROM 3 motherboard only). The catch: this register is fiddled with by the monitor firmware, so you can't reliably read it from the command line. The best way to read it is to use a small machine code routine to read the register and save it elsewhere. For example (don't type the prompts, but you do need the leading spaces in the mini-assembler): ]CALL-151