Re: [cc65] Lynx target

From: "Karri Kaksonen" on Thursday, March 20, 2008; at 05:20 AM -0400
>
> The Lynx file I/O is a bit different from other systems, as the directory
> contains the RAM address where to load the data upon request.  So, there
> are really just two basic commands you use:
>
> void __fastcall__ FileLoadFile(int filenumber)
> void __fastcall__ FileExecFile(int filenumber)

I think that those functions should be renamed CartLoadFile() and
CartExecFile().  It will avoid confusion about the source of what they load.

There are three sources of programs:
1. cartridges,
2. ComLynx serial cables,
3. emulators can load from a host's file-system.

Those functions' names should show that they read from the first source.

>
> Typical Lynx "files" are linked into a cartridge image as named segments.
> "File" number - description:
> 0 - title sprite, mandatory
> 1 - start-up executable, mandatory (also contains all the cc65
> resident libraries)
> 2 - miniloader library remains resident between $0200-$03ff for
> accessing the cart.
> 3 - first game executable, starting at $0400 (it does not contain the
> cc65 resident libraries)
> 4 - second game executable, starting at $0400 (it does not contain the
> cc65 resident libraries)
> .....
> N - sprites for first game
> N+1 - more sprites
> N+3 - one tune -- music in ABC format, to be used for all games
> N+4 - another tune -- more music
>
> The programmer just reads in the files his level needs, and uses them.
>
> FileLoadFile(BACKGROUND_SPRITE_FILENO); // The linker knows that the
> sprite is needed in Sbackground.
> tgi_draw(&Sbackground);
> FileLoadFile(MOZART_SYMPHONY_FILENO); // The linker knows that the data
> goes to arrays mozart0..mozart3.
> abc_play(channel0, mozart0)
> abc_play(channel1, mozart1)
> abc_play(channel2, mozart2)
> abc_play(channel3, mozart3)
>
> The cc65 linker will assemble the directory, and set the addresses and
> sizes for code and data overlays.
>
> On some carts., we also have EEPROM support (128 * 16bit).
> For that, there are three functions:
> int __fastcall__ eeprom_read(unsigned char cell)
> void __fastcall__ eeprom_erase(unsigned char cell)
> void __fastcall__ eeprom_write(unsigned char cell, int data)
>
> The question I have is, can that functionality be implemented using
> some common functions found for other cc65 targets?

No, the libraries do not have common functions for direct overlay support.

However, I adapted some code from your "lynx-cart-demo-1.1.zip"
contribution, and created enough POSIX input functions to allow Lynx
programs to load dynamic drivers (into heap space) in the same way that
other targets do it.  Examples:

    // The joystick and graphics drivers are the third and fourth files
    // in the directory.
    status = joy_load_driver(joy_stddrv);
    tgi_load_driver("\3");

It might be interesting to add a layer above those EEPROM functions that
sees the EEPROM as a POSIX file.

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