millfork/include/c64_panic.mfk

void _panic() {
    asm {
        SEI
        PLA
        TAY
        PLA

        TAX
        JSR hi_nibble_to_hex
        JSR putchar
        TXA
        JSR lo_nibble_to_hex
        JSR putchar

        TYA
        JSR hi_nibble_to_hex
        JSR putchar
        TYA
        JSR lo_nibble_to_hex
        JSR putchar

        LDA #2
        STA $D020
    }
    while(true){}
}