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91 lines
4.3 KiB
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91 lines
4.3 KiB
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.. _portingguide:
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*************
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Porting Guide
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*************
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Here is a guide for making Prog8 work for other compilation targets.
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Answers to the questions below are used to configure the new target and supporting libraries.
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**It is not required to change the compiler itself to make it support new compilation targets.**
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A few of the most commonly used ones are built-in (such as c64, cx16), but you can use
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separate configuration files to create new targets that the compiler can use.
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See :ref:`customizable_target` for details about this. You still need to provide most of the
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information asked for in this porting guide and code that into the configuration file.
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.. note::
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The assembly code that prog8 generates is not suitable to be put into ROM. (It contains
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embedded variables, and self-modifying code).
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If the target system is designed to run programs from ROM, and has just a little bit of RAM
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intended for variables, prog8 is likely not a feasible language for such a system right now.
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CPU
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---
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#. 6502 or 65C02? (or strictly compatible with one of these)
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#. can the **64tass** cross assembler create programs for the system? (if not, bad luck atm)
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Memory Map
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----------
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Zeropage
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========
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#. *Absolute requirement:* Provide four words (16 bit byte pairs) in the zeropage that are free to use at all times.
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#. Provide list of any additional free zeropage locations for a normal running system (BASIC + Kernal enabled)
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#. Provide list of any additional free zeropage locations when BASIC is off, but floating point routines should still work
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#. Provide list of any additional free zeropage locations when only the Kernal remains enabled
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Only the four 16-bit zero page words are absolutely required to be able to use prog8 on the system.
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But more known available zeropage locations mean smaller and faster programs.
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RAM, ROM, I/O
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=============
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#. what part(s) of the address space is RAM? What parts of the RAM can be used by user programs?
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#. what is the usual starting memory address of programs?
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#. what part(s) of the address space is ROM?
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#. what part(s) of the address space is memory-mapped I/O registers?
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#. is there a block of "high ram" available (ram that is not the main ram used to load programs in) that could be used for variables?
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#. is there a banking system? How does it work (how do you select Ram/Rom banks)? How is the default bank configuration set?
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Character encodings
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-------------------
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#. provide the primary character encoding table that the system uses (i.e. how is text represented in memory. For example, PETSCII)
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#. provide alternate character encodings (if any)
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#. what are the system's standard character screen dimensions?
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#. is there a screen character matrix directly accessible in RAM? What's it address? Same for color attributes if any.
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ROM routines
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------------
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#. provide a list of the core ROM routines on the system, with names, addresses, and call signatures.
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Ideally there are at least some routines to manipulate the screen and get some user input (clear, print text, print numbers, input strings from the keyboard)
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Routines to initialize the system to a sane state and to do a warm reset are useful too.
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The more the merrier.
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Floating point
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==============
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Prog8 can support floating point math *if* the target system has suitable floating point math routines in ROM. If that is the case:
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#. what is the binary representation format of the floating point numbers? (how many bytes, how the bits are set up)
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#. what are the valid minimum negative and maximum positive floating point values?
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#. provide a list of the floating point math routines in ROM: name, address, call signature.
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Support libraries
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-----------------
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The most important libraries are ``syslib`` and ``textio``.
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``syslib`` *has* to provide several system level functions such as how to initialize the machine to a sane state,
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and how to warm reset it, etc.
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``textio`` contains the text output and input routines, it's very welcome if they are implemented also for
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the new target system. But not required.
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There are several other support libraries that you may want to port (``diskio``, ``graphics`` to name a few).
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Also of course if there are unique things available on the new target system, don't hesitate to provide
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extensions to the ``syslib`` or perhaps a new special custom library altogether.
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