CPU simulator written in C

[/* frank */]

I have to do a homework: make a CPU simulator using C language.

I have a set of asm instructions so I have to write a program
that should:
- load .asm file
- view .asm file
- do a step by step simulation
- display registers contents

I tried to search con google with no success.

Any help (links, tricks/tips...)
would be really appreciated.

Thanks in advance.

[Emmanuel Delahaye]

In 'comp.lang.c', /* frank */ <__*******@desp ammed.com> wrote:

I have to do a homework: make a CPU simulator using C language.

I have a set of asm instructions so I have to write a program
that should:
- load .asm file
- view .asm file
- do a step by step simulation
- display registers contents
It's a design question. There is no particular problem with that. It's just
another interpreter.
I tried to search con google with no success.

Better to dig your brain. The answer is there.

BTW, what is your question about the C-language?

--
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[Richard Bos]

/* frank */ <__*******@desp ammed.com> wrote:

I have to do a homework: make a CPU simulator using C language.

I have a set of asm instructions so I have to write a program
that should:
- load .asm file
- view .asm file
- do a step by step simulation
- display registers contents

I tried to search con google with no success.

Your assignment said: "_make_ a CPU simulator". Not "copy a CPU
simulator". There is a very good reason for this. How do you expect to
learn anything if you just hand in someone else's work?

Richard

[Case]

/* frank */ wrote:

I have to do a homework: make a CPU simulator using C language.

I have a set of asm instructions so I have to write a program
that should:
- load .asm file
- view .asm file
- do a step by step simulation
- display registers contents

I tried to search con google with no success.

Any help (links, tricks/tips...)
would be really appreciated.

The key idea is to map all parts of a CPU on C structures
and routines. For example: the program counter (PC) can
be simply mapped to an int variable. Now you should create
mappings for registers, .... It's not that complicated.

HTH

Case

[/* frank */]

Case ha scritto:

It's not that complicated.

Thanks a lot.

I was searching only for a "starting input" .

[osmium]

/* frank */ wrote:

I have to do a homework: make a CPU simulator using C language.

I have a set of asm instructions so I have to write a program
that should:
- load .asm file
- view .asm file
- do a step by step simulation
- display registers contents

I tried to search con google with no success.

Any help (links, tricks/tips...)
would be really appreciated.

You are searching with the wrong target word. The proper word is emulate,
not simulate.

To simulate is to try to predict how fast some CPU design (probably unbuilt)
will be. To emulate is to produce the effect on computer B that a program
was run on computer A. If you do not have source code for A, there are not
too many alternatives. In the real world you would have machine code, not
an asm file - which is a different thing. But it is easier to communicate
between humans with asm than with machine code.

[Dan Pop]

In <2j************ *@uni-berlin.de> /* frank */ <__*******@desp ammed.com> writes:

I have to do a homework: make a CPU simulator using C language.
Well, C is particularly suitable for such an exercise.
I have a set of asm instructions so I have to write a program
that should:
- load .asm file
- view .asm file
- do a step by step simulation
- display registers contents

I tried to search con google with no success.

Any help (links, tricks/tips...)
would be really appreciated.

Apart from being lazy, you're also stupid if you can expect any help
without specifying the CPU being emulated and the format of the .asm
files. I hope they're containing machine code and not assembly code,
because assemblying the code is, by far, the most difficult part of the
exercise.

Anyway, you can't expect any help until you describe your design and
ask very specific questions about its implementation.

Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de

[Thomas Matthews]

/* frank */ wrote:

I have to do a homework: make a CPU simulator using C language.

I have a set of asm instructions so I have to write a program
that should:
- load .asm file
- view .asm file
- do a step by step simulation
- display registers contents

I tried to search con google with no success.

Any help (links, tricks/tips...)
would be really appreciated.

Thanks in advance.

Ha! I wrote something like this at the University.

I also wrote another one at my current worksite.

Here are some techniques:
1. Allocate variables for all registers.

2. You may need variables for the databus(es) too.

3. Write a simple program that executes a simple
instruction, such as adding two registers.

3.1 This may involve writing a function that simulates
a hardware adder. In my case, I had to put a value
onto a databus, have the adder retrieve from the
databus and repeat for the other argument. Another
function would trigger the actual addition, then
another function puts the sum onto the databus.

4. Once you get the above working, add a new feature
and test it. The paradigm of "Test Driven Development"
says to write the test first and expect the first
invocation to fail, since you haven't written the
code yet.

If you have a windowing operating system, you could
display the register contents and the databus contents
in separate windows.

--
Thomas Matthews

C++ newsgroup welcome message:
http://www.slack.net/~shiva/welcome.txt
C++ Faq: http://www.parashift.com/c++-faq-lite
C Faq: http://www.eskimo.com/~scs/c-faq/top.html
alt.comp.lang.l earn.c-c++ faq:
http://www.raos.demon.uk/acllc-c++/faq.html
Other sites:
http://www.josuttis.com -- C++ STL Library book

[Case]

/* frank */ wrote:

Case ha scritto:

It's not that complicated.

I was searching only for a "starting input" .

That's what I thought. Good luck!

Case

[RoSsIaCrIiLoIA]

On Wed, 23 Jun 2004 07:35:41 +0200, /* frank */
<__*******@desp ammed.com> wrote:

I have to do a homework: make a CPU simulator using C language.

I have a set of asm instructions so I have to write a program
that should:
- load .asm file
- view .asm file
- do a step by step simulation
- display registers contents

I tried to search con google with no success.

Any help (links, tricks/tips...)
would be really appreciated.

Thanks in advance. I googled eax ebx ecx edx ax bx in com.lang.c
-->
_______________ ________
In article <19************ *******@darwin. ntu.edu.au> cj*@dme.nt.gov. au
writes:I have repeatedly come across declarations of
the type 'struct REGS' (i think that was what was called,
have seen a few variations) and was wondering if
someone could tell me it's contents, and what it is used for.
I only have a very basic shareware compiler (for my PC anyway,
and I have never seen it under Unix) and it has no mention of this
structure.

Could someone enlighten me ?

This is not a Unix item but strictly a PC item as follows:

union REGS {
struct WORDREGS x;
struct BYTEREGS h;
};

struct WORDREGS {
unsigned int ax, bx, cx, dx;
unsigned int si, di, cflag, flags;
};

struct BYTEREGS {
unsigned char al, ah, bl, bh;
unsigned char cl, ch, dl, dh;
};

These structures allow C programs on PCs to access the CPU registers.

AX,BX,CX,DX,SI, DI,CF(carry flag),and FLAGS are all Intel 80x86
registers
AL/AH,BL/BH,CL/CH,DL/DH are pseudo 8 bit registers which are derived
from the
AL = Low half of AX, AH = High half of AX, etc.

The basic registers are 16 bits while the extended registers are 32
bits
EAX,EBX,ECX,EDX , etc.

In addition you have the segment registers CS,DS,ES,SS and the
pointers
SP,BP plus the index registers SI,DI and on the 80386 and above you
also
have debug registers.

In protected mode the segment registers become selector registers.

The segments are as follows:
CS code segment
DS data segment
ES extra segment
SS stack segment

The pointers are:
SP stack pointer
BP base pointer
--
Scott Hopson (sc****@filenet .com)
_______________ _______________ ______________

Hi,

I am not really familiar with interrupt calls, especially when done in
a 32 Bit OS enviroment.

I using the WatCom C Compiler Ver. 11b building 32 Bit Dos
applications.

I am trying to call interrupt 2FH, function 0DH for detecting the
driveletters of all connected cdroms.

I programmed this under 16bit dos and it works well, but I am not sure
how to adapt it for 32 Bit.

I have enclosed the code for 16 Bit. I would be pleased if anyone can
give advice.

Thanks a lot in advance.

Philipp

{
union REGS regs;
struct SREGS sregs;
char driveLetters [27];

regs.x.ax = 0x150D;
sregs.es = FP_SEG (driveLetters);
regs.x.bx = FP_OFF (driveLetters);
int86x (0x2F, &regs, &regs, &sregs);
}

*************** *******
* Auszug aus <i86.h> *
*************** *******
struct DWORDREGS {
unsigned int eax;
unsigned int ebx;
unsigned int ecx;
unsigned int edx;
unsigned int esi;
unsigned int edi;
unsigned int cflag;
};
struct WORDREGS {
unsigned short ax; __FILLER(_1)
unsigned short bx; __FILLER(_2)
unsigned short cx; __FILLER(_3)
unsigned short dx; __FILLER(_4)
unsigned short si; __FILLER(_5)
unsigned short di; __FILLER(_6)
#if defined(__WINDO WS_386__)
unsigned short cflag;
#else
unsigned int cflag;
#endif
};
struct BYTEREGS {
unsigned char al, ah; __FILLER(_1)
unsigned char bl, bh; __FILLER(_2)
unsigned char cl, ch; __FILLER(_3)
unsigned char dl, dh; __FILLER(_4)
};
union REGS {
#if defined(__386__ ) && !defined(__WIND OWS_386__)
struct DWORDREGS x;
#else
struct WORDREGS x;
#endif
struct WORDREGS w;
struct BYTEREGS h;
};
struct SREGS {
unsigned short es, cs, ss, ds;
#if defined(__386__ )
unsigned short fs, gs;
#endif
};