I have been slowly working on getting a MUSL compiler that targets the MU5 emulator, with the ultimate goal of compiling the MUSS source code to run on it. The first step is to build a cross compiler that works on Windows. A while back I switched tactic from building my own Flex/Bison compiler, to hand translating the MUSL compiler into C. I completed that translation a few months ago.

I then started testing the translated compiler, parsing some sample MUSL code. I found a lot of mistranslations, of course. I also found a couple of spots where I could not reconcile the code with the way it was supposed to work. A couple of the IF statements had to be inverted, I have marked these in the translated code with “/**/” and an explanatory comment.

I translated the MUBL module too, so that it would output a form of intermediate binary code, however I think I should not have bothered. This is because, more recently, I switched to parsing very simple programs and building an actual implementation of MUTL that targets the emulator.

Today I succeeded in compiling the following  program which runs on the MU5 emulator and outputs a simple “hello world” message.

*TLSEG 0 %FFFF %00010000 0 6;
*TLSEG 1 %FFFF 0 0 6;
*TLLOAD 1 0;
*GLOBAL 0;
*CODE 1;
*VTYPE LOGICAL64;
MODULE;
VSTORE CONSOLE.INTERRUPT %300;
VSTORE TELETYPE.DATA %306;
VSTORE TELETYPE.CONTROL %307;
$PS PRINT.STRING(ADDR[LOGICAL8]);
PRINT.STRING(%"HELLO MU5 WORLD$L");
HALT: -> HALT;
PROC PRINT.STRING(STRING);
    $IN I;
    FOR I < 16 DO
        %F => CONSOLE.INTERRUPT; :: Reset console interrupt bits
        0 => TELETYPE.CONTROL; :: TTY output mode
        STRING^[I] => TELETYPE.DATA;
        WHILE CONSOLE.INTERRUPT = 0 DO OD;
    OD
END
*END

The code is naïve and relies on a tweak to the emulator not to generate an interrupt when the teletype character has been written. Note also that the built-in SIZE function does not work, I have not been able to work out how it is supposed to work yet.