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From: jeff@abnji.UUCP (jeff)
Newsgroups: net.micro,net.arch
Subject: what really happens during a bus acknowledge?
Message-ID: <650@abnji.UUCP>
Date: Mon, 20-May-85 14:02:07 EDT
Article-I.D.: abnji.650
Posted: Mon May 20 14:02:07 1985
Date-Received: Tue, 21-May-85 06:54:51 EDT
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Xref: watmath net.micro:10446 net.arch:1222

[interrupt request acknowledged!]

An honest question:

	When a cpu (such as the 8086, 68k,etc) acknowledges a bus request,
does it halt internal execution with the bus acknowledge, or after
the bus acknowledge only when bus activity is needed (deferring prefetch
if necessary)?

	example: The instruction queue/cache is full of register to register
(or other internal) instructions when the bus request is acknowledged.
Will it execute them while the bus is relinquished?  Chips with on-chip
cache can do a lot with no external bus action.  Did anyone bother to
make the control section sophisticated enough to handle this?
It would be a real boon to multi-processor applications!

	I see that the reasoning to on-chip memory and peripherals is so
the local and global busses can be relinquished and still have the CPU
do some non-trivial work, as well as a speed advantage and less synchronization.
Is anyone using this capability to its fullest?

				Jeff 'I really wanna know' Skot
				at foggy ATT IS Somerset, NJ
				{ihnp4 | mcnc | cbosgb} abnji ! jeff