* Docs say that CLK_TCK is an obsolete alias of CLOCKS_PER_SEC so there's no point in individual definitions.
* All targets determining the clock rate at runtime can use a common handling.
Please refer to https://github.com/cc65/cc65/pull/532 for background info.
I wrote in https://sourceforge.net/p/cc65/mailman/message/35873183/
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cputs() wraps to the next line if the strings is too long to fit in the current line. I don't know if it's worth the effort to allow cpeeks() to continue reading from the next line. I'd like to discuss this aspect with the actual implementers.
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This is still as unclear today as it was when I wrote the above. Therefore this change just doesn't add cpeeks() at all.
Since f8c6c58373 the Apple II CONIO implementation doesn't "need" revers() anymore - meaning that (nearly) every possible value can be placed in VRAM with a straight cputc() (without the need for a previous revers(1)).
The implementation of cpeekc() leverages that cputc() ability by always returning the value that can be fed into cputc() without a previous revers(1). Accordingly, cpeekrevers() always returns 0.
So after the sequence revers(1); cputc(x); a cpeekc() will return a value different from x! However, I don't see this behavior braking the cpeekc() contract. I see the cpeekc() contract being defined by the sequence textcolor(cpeekcolor()); revers(cpeekrevers()); cputc(cpeekc()); placing the very same value in VRAM that there was before. And that contract is fulfilled.
The driver requires a special linker configuration: "vic20-tgi.cfg".
The VIC-20 computer needs at least 8K of expansion RAM!
"tgidemo.c" needed to be adjusted because the VIC-20's vertical (y) range is greater than its horizontal (x) range -- the opposite of most other platforms. Also, the circle demo would jam on the VIC-20.
The implementation is a bit tricky as it requires to take different code paths for the //e, the //c and the IIgs. Additionally the //c only provides a VBL IRQ flag supposed to be used by an IRQ handler to determine what triggered the IRQ. However, masking IRQs on the CPU, activating the VBL IRQ, clearing any pending VBL IRQs and then polling for the IRQ flag does the trick.
From "Mapping the Atari": "Size of player. POKE with zero or two for normal size (eight color clocks wide), POKE with one to double a player's width (sixteen color clocks wide), and POKE with three for quadruple width (32 color clocks wide). Each player can have its own width set."
The _textcolor() macro doesn't just turn on the macro optimization. It defines the return value of textcolor() - and that is supposed to be a COLOR_... value.
It can be used to undo what "cbm_screen_charmap.h" does. Together, those headers let you mix screen-code and PetSCII string and character literals in a C source file's Assembly output.
Changed the number literals from Assembly format to C format. Swapped the (upper-/lower-case) mappings of letters because the header converts from ASCII, not PetSCII.
Most documentation say that most of the bits are normally set to 1 or 0,
so just mentioning that in the comments.
A.N.A.L.O.G. issue 59 (April 1988) "Bits & Pieces" column, "Atari Zucchini"
(https://www.atarimagazines.com/analog/issue59/bits_pieces.php) implies
that they are used for specific things, but it's not clear enough to be
useful (or specifically states "Too complex and not pertinent").
This is probably sufficient for most purposes; if any PIA / PACTL/PBCTL
experts pop up, they can tell us exactly how those 4 bits can be utilized.
Use a C "union" to give both read (NMIST) and write (NMIRES) labels
to their shared register in ANTIC. (h/t @groessler).
Consolodate duplicated color definitions (HUE_..., COLOR_... and TGI_COLOR_...;
and the "_gtia_mkcolor()" macro), found in both "atari.h" and "atari5200.h",
moving it to "_gtia.h", which they both share (and which makes the most sense).
Cleaned up comments in Atari 8-bit headers.
Internal keycodes (POKEY's KBCODE) were already #defined in atari.h,
so didn't need a whole new set in _pokey.h.
Relocated register #define'd values outside of the structs,
improved comment format, expanded & corrected some things.
h/t Trevin Beattie (https://user.xmission.com/~trevin/) for the PIA
register descriptions.
Some register #defines for PIA.
(Some may be too Atari-centric -- I know PIA chip was used by PET &
perhaps other platforms supported by cc65. If so, perhaps we can
define them elsewhere. Not sure whether they'd be the same for 5200;
I admit I know zilch about that system except that it's _more or less_
an Atari 400)
Add #defines for certain registers' values.
Also add #defines for internal keyboard codes (unrelated to ATASCII;
e.g. [Q] = 47, [W] = 46, [Shift] adds 64, etc), as seen in KBCODE.
There aren't really standard color names (e.g., Compute!'s Mapping the Atari and First Book of Atari Graphics have different names), and exact colors shown depend on the system & device, anyway. Added a note.
* DMACTL - playfield size, DMA access, PMG resolution
* CHACTL - inverted text, inverse effects
* NMIEN
Also, added #define equivalents for Display List mode line instructions
based on Atari 8-bit OS (aka Atari BASIC "GRAPHICS" command) values
(e.g., "DL_GRAPHICS0" == "DL_CHR40x8x1").
Added some more documentation in the comments.
Added macros with assembly language for the start/end of Display List
Interrupt (DLI) functions.