Thanks. Then I got how you meant it. And that makes total sense.
Johnny
On 2019-09-22 19:57, Bob Supnik wrote:
If the MMU is enabled, the instructions use PSW<prev_mode> to compute
the source/destination operand physical address (if memory) or the stack
pointer to use (if SP). If the MMU is off, PSW<prev_mode> only matters
if the source/destination operand is SP.
/Bob
On 9/22/2019 12:00 PM, [email protected] wrote:
Message: 4
Date: Sun, 22 Sep 2019 09:01:42 +0200
From: Johnny Billquist<[email protected]>
To:[email protected]
Subject: Re: [Simh] PDP-11 -- MFPI, etc, with memory mgmt off
Message-ID:<[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
Well, technically, on a Unibus, even with the Unibus map, a DMA device
still only sees an 18-bit address. Or am I confused? But if the map is
enabled, then it will end up being able to access all 4M of memory
anyhow.
But your answer made me wonder. Are you saying that M[TF]P[DI] are not
using the previous mode bits in the PSW (when MMU is enabled)? Oh, maybe
you are saying that even if MMU is disabled, the selection of which R6
to use is still happening, based on PSW.
Johnny
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Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: [email protected] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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