CHIP-9

This is my emulator for the CHIP9 computer in the 2019 ed. of the X-MAS CTF. My focus was to write the emulator in a way that makes it both fast to implement but also fast to run. I achieved this by extensively using lookup-tables based on the op-codes (see RegistryMappings and InstructionMappings). The end result was too fast so I added a sleep of 30 millis every time clrscr is called.

I also wrote unit tests for most instructions to make sure everything works correctly. To ease this process I wrote a compiler and added some extra output instructions.

Compiling & Running

To compile your program you can do the following:

Compiler compiler = new Compiler();
InputStream compiledBytes = compiler.compileToStream(new File("my_program.chip"));

The compiler supports all the instructions in the CHIP9 specification as well as some extra output, labels for jumps/calls and comments.

When you have compiled your program you can run it using:

CHIP9 computer = new CHIP9();
computer.load(compiledBytes, 0x0000);
computer.execute();

You can of course invoke load several times, for instance if you want to use the boot rom. Additionally you can specify a UI to render into when draw/clrscr are invoked:

CHIP9 computer = new CHIP9(new ComputerFrame());
computer.load(new File(bootLoader), 0x0000);
computer.load(compiledBytes, 0x0597);
computer.execute();

To run pre-compiled roms you can use the utility RunRom bootloader_path program_path.

Implementation

The emulator implements the specification found in 'CHIP9 Manual.pdf', and additionally extends it with some extra output instructions:

Op code	Instruction	Meaning
0xE1	SOUT A	Print reg. A
0xE2	SOUT B	Print reg. B
0xE3	SOUT C	Print reg. C
0xE8	SOUT D	Print reg. D
0xF2	SOUT E	Print reg. E
0xF3	SOUT H	Print reg. H
0xF8	SOUT L	Print reg. L
0x01	SOUT BC	Print reg. BC
0x02	SOUT DE	Print reg. DE
0x10	SOUT HL	Print reg. HL
0x11	SOUT SP	Print stack pointer
0x12	SOUT M	Print memory at specified address
0x42	SOUT (HL)	Print memory at address in HL
0x3E	SOUT FLAGS	Print flags (as a byte number)

The compiler supports the extra output instructions, labels for jumps/calls and comments. Numbers can also be specified both as integers (123), hexadecimal (0x7B) and binary (0b01111011). An example of accepted source code:

# Program to sum values from 1..10

main:
    ldi A, 10
    call sum
    sout B
    jmp end

sum:
    ldi B, 0
    add B
    subi 1
    jmpnearnz 0xFB
    ret

end:
    hcf

Note that my compiler uses the prefix jmpnear instead of only jmp for near jumps.

License

This code is shared under the MIT license, see LICENSE for details.