Looking at CPUSim Running CPUSim Analysis of the CPUSim machine structure Analysis of the Wombat machines Instruction design Memory requirements Work on Wombat4w Work on Wombat5w New CPUSim analysis New instructions in Wombat4w Differences between Wombat4 and Wombat4w Hardware Microinstructions Arithmetic TransferRtoR TransferRtoA TransferAtoR Memory Access EQUs Fetch Sequence Machine instructions Differences between Wombat4w and Wombat5w Hardware Registers Microinstructions Set Increment Shift Arithmetic TransferRtoR TransferRtoA TransferAtoR Memory Access Machine Instructions

 

Looking at CPUSim

 

1/3/2005

 

Over the weekend, I have been looking at CPUSim. I need to look at that some more and get a target machine set up for my use. I see that you can include source files for assembly in another source file, and that may be enough. What I am thinking of is writing a memory management unit. I'll have to have that for object allocation.

 

It would be nice if I had a way that they could submit a jar file containing their work to me and I could link it with mine and test it. This might work after we get to chapter 4. I would need some kind or servlet or CGI interface to let them attach a file to a form and send it.

 

I think that I need to finish the study of CPU Sim and get the target machine set up before I can go any further. I could also compile chapter 8.

 

I need to try firing up CPUSim and seeing what the machines look like. To run it, it seems that all that I have to do is run (double click on) the batch file D:\uofm\c4041s2005\CPUSim3.1.17\Cpusim.bat.

 

Running CPUSim

 

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\xalan.jar

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\jhall.jar;%CLASSPATH%

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\crimson.jar;%CLASSPATH%

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\CPUSimHelp3.3.jar;%CLASSPATH%

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\acm.jar;%CLASSPATH%

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\CPUSim4.0.2.jar;%CLASSPATH%

 

java cpusim.Main

 

Analysis of the CPUSim machine structure

 

Here is an analysis of the CPUSim machine structure.

 

Analysis of the Wombat machines

 

See the analysis of Dale Skrien's Wombat machines.

 

I may need to create my own version of one of these machines to make the addressing capable of handling large enough areas of RAM. I do need to recall that some of the addressing will be relative to locations on the stack. I may need to add instructions to access off the frame pointer.

 

Instruction design

 

Memory requirements

 

See a table of the number of bytes or registers that can be addressed by a register or field of a given width.

 

I want enough memory available so that I can compile reasonable programs. If I use two byte instructions, or 16 bits, I have very little to work with. So I'm inclined to start with three byte instructions and try it from there. If I don't need the full 8 bits of the first instruction for the opcode and other operands, it won't hurt to have extra bits for the address.

 

I also have to remember that if I use multiple bytes for a value, as Java uses four bytes per slot, then I have to keep my word size in mind as I calculate addresses. This also cuts down the number of values that I can have. I could represent ints as 4 bytes and booleans as 4 bytes. If I do something different, then I probably have to include more instructions in the machine.

 

I also have to remember that I must leave enough bits in the instruction to address the registers in register arrays that I use.

 

Work on Wombat4w

 

This page describes my Wombat4w design.

 

Work on Wombat5w

 

This page describes my Wombat5w design.

 

New CPUSim analysis

 

2/2/2007

 

There is CPUSim material in both E:\CPUSim4.0.2, mainly docs, and E:\c4041s2007\cpusim4.0.2, mainly jars.

 

Files in E:\c4041s2007\cpusim4.0.2

 

acm.jar looks like a drawing package.

CPUSim3.1InstrManualfolder.zip Has the various wombat machines.

CPUSim4.0.2.jar is the main jar, containing a cpusim.Main class.

CPUSim4.02.zip contains the material that is expanded in E:\CPUSim4.0.2.

CPUSimHelp3.3.jar is a bunch of HTML files, not classes.

crimson.jar An XML package

file(2).txt Dale Skrien's letter explaining the changes in CPUSim

jhall.jar Some kind of help mechanism

xalan.jar XSL and XML processing

 

So I guess I need all of these in a class path.

 

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\xalan.jar

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\jhall.jar;%CLASSPATH%

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\crimson.jar;%CLASSPATH%

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\CPUSimHelp3.3.jar;%CLASSPATH%

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\acm.jar;%CLASSPATH%

set CLASSPATH=E:\c4041s2007\cpusim4.0.2\CPUSim4.0.2.jar;%CLASSPATH%

 

java cpusim.Main

 

I tried it, and it popped up a large, empty window with some menus.

 

It gave an error creating the help window. No further specifics.

 

Maybe it needs the help jar file in the class path. I'll try it again.

 

I still got an error.

 

4:55 Well, I don't understand the problem with the help.

 

4:59 I added the CPUSimHelp3.3.jar to the class path, and now the help works.

 

Well, it opened my machine, and it seems that it "works" so far. But now comes the hard part. I have to analyze the machines in great detail.

 

New instructions in Wombat4w

 

load_h (13) A1 A2 const ; 13 bit const: +-4096

Heap[A[op2]+op3]->A[op1]

 

store_h (14) A1 A2 const ; 13 bit const: +-4096

A[op1]->Heap[A[op2]+op3]

 

The idea is that A1 holds whatever we want to load or store, A2 holds the base address of the object on the heap, and the const (op3) is the fixed offset from the base address.

 

Wombat4w may be enough to compile to.

 

Differences between Wombat4 and Wombat4w

 

Hardware

 

The register sizes were increased.

 

Microinstructions

 

Arithmetic

 

Added mar+buf1->mar.

 

TransferRtoR

 

Several differences, added top->mar.

 

TransferRtoA

 

Some differences, none added.

 

TransferAtoR

 

Some differences, added A[ir(8-10)]->buf1.

 

Memory Access

 

Added Heap[mar]->mdr and mdr->Heap[mar].

 

EQUs

 

Fetch Sequence

 

Increment the pc by 3 instead of 2.

 

Machine instructions

 

Needs analysis.

 

Added registers A4 through A7.

 

Differences between Wombat4w and Wombat5w

 

Hardware

 

Registers

 

Wombat5w drops the top register and adds abuffer1 and nextHeap, both of 16 bits. This looks somewhat inconsistent since nextHeap will refer to the heap as top did to the stack.

 

Microinstructions

 

Set

 

It adds clear-buf2.

 

Increment

 

It replaces Inc4-top and dec4-top by Inc4-A[7] and dec4-A[7].

 

Shift

 

It adds buf1 RSA 16 and buf2 RSA 18.

 

Arithmetic

 

It drops top+mar->top and top-mar->top and adds A[7]+mar->A[7], A[7]-mar->A[7], and abuf1+buf2->abuf1.

 

TransferRtoR

 

It drops top->mar and adds abuf1->nextHeap, buffer1(16-31)->mar, ir(10-23)->buffer2(0-13), ir(8-23)->buf1(0-15), and nextHeap->buf2(16-31).

 

TransferRtoA

 

It adds buf1->A[ir(7-9)] and buf2->A[ir(21-23)].

 

TransferAtoR

 

It adds A[ir(7-9)](16-31)->abuf1 and A[ir(7-9)]->buf1.

 

Memory Access

 

Replaces top->mdr by A[7]->mdr and mdr->Stack[top] by mdr->Stack[A[7]]. Adds Stack[mar]->mdr and >mdr->Stack[mar].

 

Machine Instructions

 

Needs analysis.