How to use cp8299x simulator

command line sim file.s

The simulator takes object code input file in S-format. It executes the instructions step by step and shows all the registers and flags. A jump to subroutine 1001 (JSR 1001) will stop the simulator.

Limit

The number of instruction executed is limited to 20,000 instructions in case there is an infinite loop. The memory is 1000 bytes.

The simulator implements a Big Endian representation ( Hi byte first). When pushing 16 bits value into the stack, Lo byte will be pushed first then Hi byte (so that the number in the data segment and stack segment will be ordered in the same way).

The output in trace mode displayed PC, instruction, AC, SP, and flags. All numbers are in hexadecimal.

The simulator has a simple command line mode, with the following commands:

g [go] start executing a the current pc, initially pc = 0
t [single step] execute one instruction and display
d ads n [dump DS] dump memory at ads, n bytes
b ads [set breakpoint] set breakpoint at ads
c [clear breakpoint] clear breakpoint
z 1/0 [on/off display] turn on/off display
q [quit] quit the simulator
h [help] get help message

Example of a session

This is the sample session of running "asgm1.txt" (the first example in the lecture). First assemble "asgm1.txt".

c> asm asgm1.txt

this will generate two files: asgm1.lst and asgm1.s

Here is asgm1.lst

0000 : 4C 0100    jmp begin
               a: 0
               b: 10
               c: 20
               begin:
0100 : 1C 0004    lda b   ;; lda direct
0103 : CC 0005    add c
0106 : 3C 0003    sta a
0109 : 7C 03E9    jsr 1001

It shows the address on the left, and the opcode and operand, then the source line.

Start the simulator with the object code "asgm1.s"

c> sim asgm1.s

We will single step through the whole program. When it finished by executing "jsr 1001", the simulator prints "stop". Each step the simulator displays PC, opcode, AC, SP, carry and zero flag (all in hex numbers). The SP starts at the end of memory and works downward.

C:\prabhas\BAG\Chip\cp8299x\test>sim asgm1.s
>t
pc:0000 JMP A:00 SP:03E7 C0 Z0
>t
pc:0100 LDA A:0A SP:03E7 C0 Z0
>t
pc:0103 ADD A:1E SP:03E7 C0 Z0
>t
pc:0106 STA A:1E SP:03E7 C0 Z0
>t
stop
pc:0109 JSR A:1E SP:03E7 C0 Z0

We inspect the content of memory to see the result of executing the program. The variable "a" (at address 5) is 1EH (30) which is the expected result. We exit the simulator by "q".

>d 0 10
0000 : 4C 01 00 1E 0A 14 00 00 00 00
000A : 00 00 00 00 00 00
>q

C:\prabhas\BAG\Chip\cp8299x\test>

There are many examples in the directory "test" will all examples you found in the class. Enjoy reading and try them out.

Input is not robust, that is, if you type everything correctly, it works as expect, if you input something wrong, it probably cannot recover. The simplest way is to restart it. Please report any bug to me. I will update it as soon as I get the report. Evenbetter if you fix it yourself and let me know. The main simulator "cpu5.c" is less than 200 lines long, the command line interpreter "mon.c" is 100 lines long. Tweak it as you please. Enjoy!

Prabhas Chongstitvatana
18 December 2005