In the previous sections we have listed all the available MIX binary instructions. As we have shown, each instruction is represented by a word which is fetched from memory and executed by the MIX virtual CPU. As is the case with real computers, the MIX knows how to decode instructions in binary format (the so–called machine language), but a human programmer would have a tough time if she were to write her programs in machine language. Fortunately, the MIX computer can be programmed using an assembly language, MIXAL, which provides a symbolic way of writing the binary instructions understood by the imaginary MIX computer. If you have used assembler languages before, you will find MIXAL a very familiar language. MIXAL source files are translated to machine language by a MIX assembler, which produces a binary file (the actual MIX program) which can be directly loaded into the MIX memory and subsequently executed.
In this section, we describe MIXAL, the MIX assembly language. The implementation of the MIX assembler program and MIX computer simulator provided by MDK are described later on (see Getting started).
|• Basic structure||Writing basic MIXAL programs.|
|• MIXAL directives||Assembler directives.|
|• Expressions||Evaluation of expressions.|
|• W-expressions||Evaluation of w-expressions.|
|• Local symbols||Special symbol table entries.|
|• Literal constants||Specifying an immediate operand.|