Hello World Tutorial

This is the smallest useful Cat Assembly program: load a pointer to a null-terminated string into r1, then call interrupt 0x80 to print it.

#const INT_PRINT, 0x80

start:
    mov r1, hello_msg    ; r1 = pointer to C-style string
    int INT_PRINT        ; VM prints string at address in r1

halt:
    jmp halt             ; keep CPU alive (simple infinite loop)

hello_msg:
    dstr "Hello, World!\n\0"

How it works

1. #const INT_PRINT, 0x80 gives the print interrupt a readable name.
2. mov r1, hello_msg places the assembled address of hello_msg into r1.
3. int INT_PRINT invokes the VM stdout handler, which reads bytes from r1 until \0.
4. dstr "Hello, World!\n\0" emits the message bytes, including newline (\n) and terminator (\0).
5. jmp halt prevents execution from falling through into string data.

Build and run (CatLauncher)

catasm hello.cat -o hello.bin
catlaunch run --rom hello.bin

Expected output:

Hello, World!