8-bit Sandboxed HelloWorld CPU Emulator

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mrminecrafttnt
Posts: 95
Joined: Feb 11, 2013 12:23

8-bit Sandboxed HelloWorld CPU Emulator

Postby mrminecrafttnt » May 17, 2021 14:56

This thing represents a minimalistic coustom CPU emulator to print an 'Hello World'
I think that is a good basepoint to write an more complex emulator.

Code: Select all

dim shared as ubyte r0,r1,exitflag,prgctr,ram(256)
sub cpu
    do
        'case x = opcode
        select case ram(prgctr)
        case 0
            print chr(ram(r0));
        case 1
            r0+=1
        case 2
            r0 = ram(prgctr+1)
            r1 = ram(prgctr+2)
            prgctr+=2
        case 3
            prgctr=ram(prgctr+1)-1
        case 4
            if r0 = r1 then exitflag = 1
        case else
            print "UNKNOWN OPCODE (";ram(prgctr);") @ ";prgctr
        end select
        prgctr+=1
    loop until exitflag = 1
end sub

'compiler instructions
sub wr(value as integer)
    ram(prgctr)=value
    prgctr+=1
end sub

sub compile_print
    wr 0
end sub

sub compile_inc_r0
    wr 1
end sub

sub compile_setup (startadr as ubyte,endadr as ubyte)
    wr 2
    wr startadr
    wr endadr
end sub

sub compile_jmp (adr as ubyte)
    wr 3
    wr adr
end sub

sub compile_compare
    wr 4
end sub

sub compile_string(msg as string)
    for i as integer = 0 to len(msg)-1
        wr msg[i]
    next
end sub

'lets compile the firmware
dim as string message = "Hello World"
compile_jmp 2 + len(message)
compile_string message
compile_setup 2,1 + len(message)
dim as ubyte mainloop = prgctr
compile_print
compile_compare
compile_inc_r0
compile_jmp mainloop


'lets run :)
prgctr = 0
cpu
sleep

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