8.7 KiB
apple1-videocard-lib
Library and demos for the "Apple-1 Graphic Card" by P-LAB, featuring the TMS9918 Video Display Processor by Texas Instruments.
Repo structure
demos/
demo/ demo program that makes use of the library
picshow/ demo program that shows a picture in bitmap mode
tetris/ a game
docs/ TMS9918 and Apple-1 manuals
kickc/ target configuration files for KickC
lib/ the library files to include in your project
tools/ some build tools
Introduction
The library is a set of C routines that make very easy
to use the TMS9918 on the Apple-1. It is intended to work
with the "Apple-1 Graphic Card" board by P-LAB or any
other video card that maps the TMS9918 in the $CC00
-$CC01
memory range of the Apple-1.
The library is written in C with KickC, a very efficient 6502 C compiler.
Choice of the screen mode
The library supports screen modes 1 and 2 only (screen 0 and screen 3 not being very useful). Both are 256x192 pixels but there are some differences you should consider when evaluating which mode to use:
-
Screen 1: there are 256 tiles that can be written very quickly on the screen, but the color choice is limited to 8 consecutive tiles for each color in the palette. It's commonly used for text applications with limited colors.
-
Screen 2: you can address every pixel on the screen with a limitation of 2 colors per line within an 8x8 tile grid. It's commonly used for bitmapped graphic or slow-but-colorful text.
Both screen modes support 32 sprites.
Working with screen 1
Some example code:
// *** first we set the SCREEN 1 mode
tms_init_regs(SCREEN1_TABLE); // initializes the registers with SCREEN 1 precalculated values
screen1_prepare(); // prepares the screen to be used, loads a useful 8x8 ASCII font
tms_set_color(COLOR_VIOLET); // sets border color to violet (see tms9918.h for the list of all colors)
// *** then we can use it
screen1_cls(); // clears the screen
screen1_putc('A'); // writes the character "A"
screen1_putc(CHR_BACKSPACE); // goes back 1 character
screen1_putc('B'); // overwrites a "B" over it
// writes "A" in the bottom-right corner, causing the screen to scroll
screen1_locate(31,23);
screen1_putc("A");
// some printing
screen1_puts(CLS "Hello world"); // CLS, REVERSE_ON, REVERSE_OFF
screen1_puts(REVERSE_ON "reverse" REVERSE_OFF); // are macros defined in tms_screen1.h
screen1_puts("Line1\nLine2"); // '\n' is also supported
// simple string input from the keyboard (editing with CTRL-H is also supported)
char buffer[32];
screen1_strinput(buffer, 32);
screen1_prints("you wrote:");
screen1_prints(buffer);
Working with screen 2
Some example code:
// initializes the registers with SCREEN 2 precalculated values
tms_init_regs(SCREEN2_TABLE);
// sometimes two colors need to be packed into a single byte
// you can easily do that with the FG_BG() macro:
byte mycolor = FG_BG(COLOR_BLACK,COLOR_WHITE);
// prepares the screeen to be used as a bitmap with default colors black on white
screen2_init_bitmap(mycolor);
// plots a pixel in the middle of the screen
screen2_plot(128,96);
// and erases it:
screen2_plot_mode = PLOT_MODE_RESET; // PLOT_MODE_INVERT is also supported
screen2_plot(128,96);
screen2_plot_mode = PLOT_MODE_SET;
// draws a diagonal line
screen2_line(0,0,255,191);
// writes a character from the embedded FONT
byte col = FB_BG(COLOR_DARK_RED,COLOR_LIGH_YELLOW);
screen2_putc('A', 31, 23, col);
// writes a string
screen2_puts("HELLO", 16, 12, col);
// note: screen2_putc() and screen2_puts() are fast but they
// can only print characters aligned within the 8x8 grid
Working with VRAM directly
Some example code:
// writes the value 42 at VRAM location 8000
tms_set_vram_write_addr(8000);
TMS_WRITE_DATA_PORT(42);
// and re-reads it
tms_set_vram_read_addr(8000);
byte val = TMS_READ_DATA_PORT;
When using the default values that came with SCREEN1_TABLE[]
and SCREEN2_TABLE[]
,
VRAM is organized according the following memory map:
// ZONE RANGE NAME YOU CAN USE IN C
// ===========================================================
// pattern table $0000-$17FF TMS_PATTERN_TABLE
// sprite patterns $1800-$19FF TMS_SPRITE_PATTERNS
// color table $2000-$27FF TMS_COLOR_TABLE
// name table $3800-$3AFF TMS_NAME_TABLE
// sprite attributes $3B00-$3BFF TMS_SPRITE_ATTRS
// example: writes the bitmap value 10101010 on row 3 of pattern 4
tms_set_vram_write_addr(TMS_PATTERN_TABLE+4*8+3);
TMS_WRITE_DATA_PORT(0b10101010);
Working on a more low-level
Setting the TMS9918 registers
// you can set a TMS9918 register directly with:
tms_write_reg(7, 0x1F);
// which also saves the written value to a buffer
// because the TMS does not allow to read from
// its registers (they are write-only)
byte oldvalue = tms_regs_latch[7];
Working directly with the I/O chip interface
If you want to program the VDP directly you can use the following utility functions:
TMS_WRITE_CTRL_PORT(value); // writes a byte to the control port ($CC01)
TMS_WRITE_DATA_PORT(value); // writes a byte to the data port ($CC00)
byte value = TMS_READ_CTRL_PORT; // reads the status register ($CC01)
byte value = TMS_READ_DATA_PORT; // reads a byte from the data port ($CC00)
Miscellaneous functions
tms_wait_end_of_frame(); // waits the end of video frame, for timimng or sync video updates
tms_set_blank(1); // turns on video blanking (0 restores normal view)
tms_set_external_video(1); // turns on/off external video input
tms_set_interrupt_bit(1); // enable end of frame interrupts generation
(TODO: interrupt functions)
Apple-1 utility functions
There are also utility functions to interact with the Apple-1 screen and keyboard:
// prints hex "F3" on the Apple-1 screen
woz_print_hex(0xF3)
// prints "A" on the Apple-1 screen
woz_putc('A');
// prints "HELLO" on the Apple-1 screen
woz_puts("HELLO");
// gets a key from the keyboard (waits for it)
byte k = apple1_getkey();
// non blocking keyboard read: do something until RETURN is hit
while(1) {
if(apple1_iskeypressed()) {
if(apple1_readkey()==0x0d) break;
}
else do_something_else();
}
Building the source code
To link the library, simply #include
the tms9918.h
file
in your C sources. The recommended way is to add the KickC
command line switch -includedir=thisrepo/lib
to your
build script and then include the file with #include <tms9918.h>
.
The the tools/
directory contains a simple build.bat
script
example (for Windows) that you can customize to your needs.
Setting a machine target
There are three configurations you can target with
the switches -t target -targetdir thisrepo/kickc
of the KickC compiler:
apple1
apple1_jukebox
vic20
Target "apple1"
With this target, the compiled program will start at $0280
in
the free RAM of the Apple-1 (please make sure you have enough RAM).
(TODO: add reference to hexdump.js
)
Target "apple1_jukebox"
This target is for expansion cards that provide a ROM storage in
the range $4000
-$7FFF
, as:
- the "CodeTank" EEPROM daughterboard of the "Apple-1 Graphic Card"
- "Juke-Box Card" FLASH
In this target configuration, the program is split into two segments:
- the
Code
that resides in ROM at$4000
- the
Data
that resides in RAM at$0280
The split is required because the program needs to write on the Data
segment (e.g. when changing the value of a variable).
The only issue is that the "Data" segment needs to be initialized
with the correct startup values (for example, the value that
a global int
variable takes before it's used).
The "Data" initialization needs to be done manually in the C program
by explicitly calling apple1_eprom_init()
in main()
. The function
will copy the ROM portion $7582-$7FFF into the "Data" segment at $0280-$0FFF.
The initialization values in the ROM range $7582-$7FFF are generated with
the build script mkeprom.js
which creates a fixed-length 16K binary file
to be put on the EEPROM/FLASH.
Below is a recap of the memory map for this target:
$0000-$00FF zero page: holds some C program variables $0280-$0FFF RAM: C program "Data" segment $4000-$7581 ROM: C program "Code" segment $7582-$7FFF ROM: C program "Data" segment (startup values)
Target "vic20"
This target has been used during the development of the library where a custom made VIC-20 emulator was interfaced with an emulated TMS9918, thus allowing running tests when the real Apple-1 machine was not available.