support other target machines (Atari, Vic20, C-128, BBC Micro...)

[irmen]

I'd like prog8 to better support other 6502 machines as well. But I know very little of the others, and any help here would be very much appreciated

Here is a guide to help fill out the blanks required to add a new target to the compiler: https://prog8.readthedocs.io/en/latest/portingguide.html

Here is some information about the customizable compiler target feature https://prog8.readthedocs.io/en/latest/targetsystem.html#customizable-target

[irmen]

Some progress has been made here recently, by adding a switch to select the compiler output target.

[irmen]

The commanderX16 target is now the second functional target and it kinda ironed out the kinks that should make it fairly easy to add another target. (as long as we know the machine's memory map and such)

[zbyti]

Are you considering at least basic support for 8-bit Atari?

[irmen]

I would love to!!
But I don't know how they work.

What needs to be done is mainly implement the ICompilationTarget and IMachineDefinition objects for it that tell the compiler about memory layout and stuff.

[zbyti]

Safe memory location for code is from $2000 to $BFFF then BASIC is off - this is default scenario.

ZP free memory for non BASIC programs is from $80-$FF.

Key registers you can find here: https://github.com/KarolS/millfork/tree/master/include a8_*.mfk

---

Most simple binary (XEX) for Atari is build this way:

$FFFF begining-LO begining-HI end-LO end-HI [ bytes of our program ] $02E0 $02E1 start-LO start-HI

https://www.atarimax.com/jindroush.atari.org/afmtexe.html

There are other headers for multi segments programs but above is good for start :]

---

2000: 4C 03 20  JMP $2003
2003: AD 0B D4  LDA $D40B   ;VCOUNT
2006: 8D 18 D0  STA $D018   ;COLPF2
2009: 8D 0A D4  STA $D40A   ;WSYNC
200C: 4C 03 20  JMP $2003

as XEX file looks this way:

FF FF 00 20 0E 20 4C 03 20 AD 0B D4 8D 18 D0 8D 0A D4 4C 03 20 E0 02 E1 02 00 20

Header: first 6 bytes and last 6.

This way you can load one big segment into memory from $2000 to $200E and run program from $2000.

[zbyti]

Oh, well I forgot about:

E0 02 E1 02

:D

736-737          	2E0-2E1          	RUNAD

     Used by DOS for the run address read from the disk sector one or
     from a binary file. Upon completion of any binary load, control
     will normally be passed back to the DOS menu. However, DOS
     can be forced to pass control to any specific address by storing
     that address here. If RUNAD is set to 40960 ($A000), then the left
     cartridge (BASIC if inserted) will be called when the program is
     booted.

     With DOS 1.0, if you POKE the address of your binary load file
     here, the file will be automatically run upon using the DOS
     Binary Load (selection L). Using DOS 1.0's append (/A) option
     when saving a binary file to disk, you can cause the load address
     POKEd here to be saved with the data. In DOS 2.0, you may
     specify the initialization and the run address with the program
     name when you save it to disk (i.e.,
     GAME.OBJ,2000,4FFF,4F00,4000). DOS 2.0 uses the /A option
     to merge files. In order to prevent your binary files from running
     automatically upon loading in DOS 2.0, use the /N appendage to
     the file name when loading the file.

     For users of CompuServe, there is an excellent little BASIC
     program (with machine language subroutines) to create autoboot
     files, chain machine language files with BASIC and to add an 850
     autoboot file in the Popular Electronics Magazine (PEM) access
     area. It is available free for downloading.

https://www.atariarchives.org/mapping/memorymap.php

[irmen]

What type of 8 bit atari are we talking about anyway?
Also can you recommend a good emulator for it (preferably running on Linux)?

[zbyti]

Atari 800 XL 64KB RAM.

On Ubuntu I use https://atari800.github.io/ - in special cases I use Altirra under WINE.

Run atarti800 from command-line then F8 give you access to the monitor.

[zbyti]

Atari 800XL code examples:

https://github.com/zbyti/k65-playground/tree/main/src/a8

https://github.com/tebe6502/Mad-Pascal/tree/master/samples/a8

[irmen]

how to print some text to the screen on 800xl?

[zbyti]

You can take screen memory pointer from SAVMSC located at $58, $59.

Also look at:

https://github.com/KarolS/millfork/blob/master/include/a8_kernel.mfk

https://github.com/tebe6502/Mad-Pascal/blob/master/base/atari/putchar.asm

832-847          	340-34F          	IOCB0

     I/O Control Block (IOCB) zero. Normally used for the screen
     editor (E:). You can POKE 838,166 and POKE 839,238 and send
     everything to the printer instead of to the screen (POKE 838,163,
     and POKE 839,246 to send everything back to the screen again).
     You could use this in a program to toggle back and forth between
     screen and printed copy when prompted by user input. This will
     save you multiple PRINT and LPRINT coding.

     You can use these locations to transfer data to other devices as
     well since they point to the address of the device's "put one byte"
     routine. See the OS Manual for more information. Location 842
     can be given the value 13 for read from screen and 12 for write to
     screen. POKE 842,13 puts the Atari into "RETURN key mode" by
     setting the auxiliary byte one (ICAX1) to screen input and
     output. POKEing 842 with 12 returns it to keyboard input and
     screen output mode. The former mode allows for dynamic use of
     the screen to act upon commands the cursor is made to move
     across.

https://www.atariarchives.org/mapping/memorymap.php