Discussion:
Hw 6 5.2
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Neil Bell
2008-07-31 07:29:25 UTC
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Im confused regarding the ALUop0 vs ALUop1. I can't seem to figure out what
each refers to. There are ALUOp and ALUsrc outputs from the control, are
these what was meant?

Thanks for the kick in the right direction.

Neil
[Instr] Albert Chae
2008-07-31 07:49:59 UTC
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ALUOp is a 2 bit signal, so ALUop0 and ALUop1 refer to the individual
bits of ALUOp. Note that ALUOop is not ALUctr from lecture, which means
it doesn't feed directly to the ALU. ALUop + the funct field of the
instruction generate the control signal to the ALU. Refer to figure
5.12 and 5.13 for more details.

Albert
Post by Neil Bell
Im confused regarding the ALUop0 vs ALUop1. I can't seem to figure out what
each refers to. There are ALUOp and ALUsrc outputs from the control, are
these what was meant?
Thanks for the kick in the right direction.
Neil
[Instr] Albert Chae
2008-07-31 18:52:47 UTC
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Section 5.5 deals with a multicycle implementation, when problem 5.2
clearly states we are looking at the single cycle datapath. I don't know
where you are getting that ALUOp is more than 2 bits. Note that ALUOp
goes into a sub unit called "ALU Control" rather than directly into
the ALU, unlike the datapath we saw in lecture.

Albert
I felt like if you browsed all of P&H Chapter 5 they showed all these things..
I feel like adding that there is a 4 bit value for ALUop that is closer to
the actual production, I think I found that in section 5.5+, but it seems like
that bits 1 and 2 (zero based array) are equivalent to ALUop0 and ALUop2. Is
this correct? I was looking at the part of the chapter just before they
started using FSMs to diagram control of the ALU.
Post by [Instr] Albert Chae
ALUOp is a 2 bit signal, so ALUop0 and ALUop1 refer to the individual
bits of ALUOp. Note that ALUOop is not ALUctr from lecture, which means
it doesn't feed directly to the ALU. ALUop + the funct field of the
instruction generate the control signal to the ALU. Refer to figure
5.12 and 5.13 for more details.
Albert
Post by Neil Bell
Im confused regarding the ALUop0 vs ALUop1. I can't seem to figure out
what
Post by [Instr] Albert Chae
Post by Neil Bell
each refers to. There are ALUOp and ALUsrc outputs from the control, are
these what was meant?
Thanks for the kick in the right direction.
Neil
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