Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!uunet!cs.utexas.edu!rhwang
From: rhwang@cs.utexas.edu (Rwo-Hsi Wang)
Newsgroups: comp.sys.m68k
Subject: 68000 and 68010 questions
Message-ID: <8215@cs.utexas.edu>
Date: 23 Mar 90 08:23:01 GMT
Organization: U. Texas CS Dept., Austin, Texas
Lines: 38

I have two questions about the instruction execution time for 68000 and
68010.  Hope someone can give me the answers.
 
    1.  In appendix D of M68000 Programmer's Reference Manual (4th edition),
	there are some descriptions about the basic operations included in
	the number of clock periods given in the tables.  In section D.3,
	MOVE instruction execution times, the data includes instruction
	fetch, which presumably is the fetch of the move instruction itself.
	In section D.4, standard instruction execution times, the data
	includes, among other things, reading the next instruction.  If they
	are correct, how do I calculate the following pieces of codes?

	A:	move	D1,D2	; This does not include instr. prefetch.
		add	D2,D3	; What is the fetch time for this instr.?

	B:	add	D1,D2	; Since instr. prefetch has been counted,
		move	D2,D3	; is this instruction fetch time redundant?

	Each of the above instruction individually takes 4 clock periods to
	execute, according to the tables.  But how many clock periods are 
	needed in A and in B?  Do both of them take 8 clock periods?

    2.  (Question about 68010)  According to the (same) manual, it states
	(in appendix F.2, Operand effective address calculation times) that 

		Several instructions do not need the operand at an effective
	    address to be fetched and thus require fewer clock periods to
	    calculate a given effective address than the instructions that
	    do fetch the effective address operand.

	My questions is: what instructions does the above sentence refer to?
	(that is, how do I know whether an instruction need to fetch the
	effective address operand?)

Thanks for your help.

Rwo-Hsi Wang
rhwang@cs.utexas.edu