Champ - N. Harold Cham's 65C02 Profiler

This is a 6502/65C02 emulator / profiler that enables you to really get to know your APPLE ][ HiRes Graphics Mode Demo.

Features

• full, cycle-accurate 65C02 emulation
• screen output as animated GIF with exact frame timing
• average frame rate
• see how much time is spent in which subroutine
• watch variables (single variables or pairs)
• no dependencies except Ruby, gcc and Merlin32

Usage

First, make sure you have gcc, ruby and Merlin32 installed. You need to prepare a YAML file to tell champ about all source and object files and their memory locations.

Take plot3d.yaml for example (using Marc A. Golombeck's excellent 3D-Demo):

load:
    0x6000: plot3d/plot3d242.s
    0x1200: plot3d/multtab.s
    0x8400: plot3d/ldrwtab.s
    0x8900: plot3d/SINETABLE
    0x8b00: plot3d/object2.s
    0x9000: plot3d/object1.s
    0x9500: plot3d/FONT
    0xb600: plot3d/projtab.s
entry: ENTRY
instant_rts:
    - LOAD1

We specified some source files (which will get compiled automatically) and some object files along with their locations in memory (load). We also specified the entry point for our program (entry), this can be a label or an address.

Furthermore, we can disable subroutines by replacing the first opcode with a RTS (instant_rts). This is necessary in some cases because Champ does not emulate hardware and thus can not load data from disk, for example.

Running the profiler

To start champ, type:

$ ./champ.rb --max-frames 100 plot3d.yaml

This will run the emulator and write the HTML report to report.html. If you do not specify the maximum number of frames, you can still cancel the emulator by pressing Ctrl+C at any time. If you need fast results and don't need the animated GIF of all frames, specify the --no-animation flag, which will still give you all the information but without the animation.

Example report

Defining watches

You can watch registers or variables at certain program counter addresses by inserting a champ directive in a comment after the respective code line in your assembler source code. All champ directives start with an at sign (@). Here's an example (example01.yaml / example01.s):

        DSK test
        MX %11
        ORG $6000
    
FOO     EQU $8000

        JSR TEST
        RTS
    
TEST    LDA #64         ; load 64 into accumulator
        ASL             ; multiply by two @Au 
        STA FOO         ; store result @Au
        RTS

Running this example results in the following watch graphs:

Champ generates a graph for every watch. You can see the watched variable plotted against the cycles, and also the PC address, file name, and source line number of the watch as well as the subroutine in which the watch was defined.

With the @Au directive, we tell champ to monitor the A register and interpret it as an unsigned 8 bit integer (likewise, @As would treat the value as a signed 8 bit integer).

By default, all champ values get recorded before the operation has been executed. To get the value after the operation, you can write: @Au(post). Feel free to add as many champ directives as you need in a single line, each starting with a new at sign.

Global variables

In addition to watching individual registers, you can also watch global variables ((example02.yaml / example02.s)):

        DSK test
        MX %11
        ORG $6000
    
FOO     EQU $8000       ; @u16

        JSR TEST
        RTS
    
TEST    LDA #0
        STA FOO
        LDA #$40
        STA FOO+1       ; @FOO(post)
        RTS

Here, we declare the type of the global variable in the same place the variable itself is declared, using @u8@, @s8@, @u16@, or @s16@. Later, we can just watch the variable by issuing a champ directive like @FOO@. In this example, we use the (post) option to see the variable contents after the STA operation.

Here's another example with some more interesting plots (example03.yaml / example03.s):

        DSK test
        MX %11
        ORG $6000
        
FOO     EQU $8000
    
        JSR TEST
        RTS
    
TEST    LDX #$FF
        LDA #1
LOOP    TAY
        TXA
        EOR #$FF
        LSR
        LSR
        STA FOO
        TYA
        ADC FOO     ; @Au(post)
        DEX         ; @Xu(post)
        BNE LOOP

This is a small program which lets the accumulator register grow quadratically while X decreases linearly:

Two-dimensional watches

We can also watch pairs of variables by separating them with a comma in the champ directive:

        DEX         ; @Xu(post) @Au,FOO(post)

This will plot FOO against X:

Did you know?

By the way, there's a full-fledged, incremental, standalone, no-dependencies GIF encoder in pgif.c that writes animated GIFs and uses some optimizations to further minimize space. It's stream-friendly and as you feed pixels in via stdin, it dutifully writes GIF data to stdout until stdin gets closed.