lawless-legends/Docs/Tutorials/PLASMA/User Manual.md

PLASMA Programming User Manual

( Proto Language AsSeMbler for Apple)

Introduction

PLASMA is a medium level programming language targetting the 8 bit 6502 processor. Historically, there were simple languages developed in the early history of computers that improved on the tedium of assembly language programming while still being low level enough for system coding. Languages like B, FORTH, and PLASMA fall into this category. The following will take you through the process of writing, building and running a PLASMA module.

Obligatory 'Hello World'

To start things off, here is the standard introductory program:

    import STDLIB
        predef puts
    end
    
    byte hello[] = "Hello, world.\n"
    
    puts(@hello)
    done

Three tools are required to build and run this program: plasm, acme, and plvm. The PLASMA compiler, plasm, will convert the PLASMA source code (usually with an extension of .pla) into an assembly language source file. acme, the portable 6502 assembler, will convert the assembly source into a binary ready for loading. To execute the module, the PLASMA portable VM, plvm, can load and interpret the bytecode. The same binary can be loaded onto the target platform and run there with the appropriate VM. On Linux/Unix from lawless-legends/PLASMA/src, the steps would be entered as:

./plasm -AM < hello.pla > hello.a
acme --setpc 4096 -o HELLO.REL hello.a
./plvm HELLO.REL

The computer will respond with:

Load module HELLO.REL
Hello, world.

A couple of things to note: plasm only accepts input from stdin and output to stdout. To build acme compatible module source, tha '-AM' flags must be passed in. The acme assembler needs the --setpc 4096 to assemble the module at the proper address, and the -o option sets the output file. The makefile in the lawless-legends/PLASMA/src directory has automated this process. Enter:

make hello

for the make program to automate this.

Organization of a PLASMA Source File

Comments

Comments are allowed throughout a PLASMA source file. The format follows that of an assembler: they begin with a ; and comment out the rest of the line:

    ; This is a comment, the rest of this line is ignored

Declarations

The beginning of the source file is the best place for certain declarations. This will help when reading others' code as well as returning to your own after a time.

Module Dependencies

Module dependencies will direct the loader to make sure these modules are loaded first, thus resolving any outstanding references. A module dependency is declared with the import statement block with predefined function and data definitions. The import block is completed with an end. An example:

    import STDLIB
        predef putc, puts, getc, gets, cls, gotoxy
    end

    import TESTLIB
        prefef puti
        byte testdata, teststring
        word testarray
    end

The predef pre-defines functions that can be called throughout the module. The data declarations, byte and word will refer to data in those modules. Case is not significant for either the module name nor the pre-defined function/data labels. They are all converted to uppercase with 16 characters significant when the loader resolves them.

Constant Declarations

Constants help with the readability of source code where hard-coded numbers might not be very descriptive.

    const MACHID  = $BF98
    const speaker = $1000
    const bufflen = 2048

These constants can be used in expressions just like a variable name.

Predefined Functions

Sometimes a function needs to be referenced before it is defined. The predef declaration reserves the label for a function. The 'import' declaration block also uses the predef declaration to reserve an external function. Outside of an import block, predef will only predefine a function that must be declared later in the source file, otherwise an error will occur.

    predef exec_file, mydef

Global Data & Variable Declarations

One of the most powerful features in PLASMA is the flexible data declarations.

Native Functions

An advanced feature of PLASMA is the ability to write functions in native assembly language. This is a very advanced topic that is covered more in-depth in the Advanced Topics section.

Function Definitions

Function definitions must come after all other declarations. Once a function definition is written, no other globale declarations are allowed.

Module Initialization Function

After all the function definitions are complete, an optional module initiialization routine follows. This is an un-named defintion an is written in-line without a definition declaration. As such, it doesn't have parameters or local variables. Function definitions can be called from within the initialization code.

Exported Declarations

Data and function labels can be exported so other modules may access this modules data and code. By prepending export to the data or functions declaration, the label will become available to the loader for inter-module resolution.

    export def plot(x, y)
        romcall(y, 0, x, 0, $F800)
    end

Module Done

The final declaration of a module source file is the done statement. This declares the end of the source file.

Data Types

Expressions

Control Flow