# Apple ][ specific information for cc65

## Oliver Schmidt

An overview over the Apple ][ runtime system as it is implemented for the cc65 C compiler.

## 1. Overview

## 2. Binary format

## 3. Memory layout

## 4. Linker configurations

- 4.1 default config file (`apple2.cfg`)
- 4.2 `apple2-system.cfg`
- 4.3 `apple2-hgr.cfg`
- 4.4 `apple2-overlay.cfg`
- 4.5 `apple2-asm.cfg`

## 5. ProDOS 8 system programs

- 5.1 LOADER.SYSTEM
- 5.2 Heap
- 5.3 ProDOS 8 I/O buffers

## 6. Platform specific header files

- 6.1 Apple ][ specific functions
- 6.2 Hardware access

## 7. Loadable drivers

- 7.1 Graphics drivers
- 7.2 Extended memory drivers
- 7.3 Joystick drivers
- 7.4 Mouse drivers
- 7.5 RS232 device drivers

## 8. Limitations

- 8.1 DOS 3.3
- 8.2 Direct console I/O
- 8.3 Random number generator
- 8.4 Realtime clock

## 9. Other hints

- 9.1 Passing arguments to the program
- 9.2 Interrupts
- 9.3 DIO
- 9.4 Specifying file types for fopen

## 10. License

## 1. Overview

This file contains an overview of the Apple ][ runtime system as it comes with the cc65 C compiler. It describes the memory layout, Apple ][ specific header files, available drivers, and any pitfalls specific to that platform.

Please note that Apple ][ specific functions are just mentioned here, they are described in detail in the separate function reference. Even functions marked as "platform dependent" may be available on more than one platform. Please see the function reference for more information.

## 2. Binary format

The standard binary file format generated by the linker for the Apple ][ target is an AppleSingle file. The default load address is $803.

AppleCommander 1.4.0 or later (available at https://applecommander.github.io/) includes the option `-as` that allows to put AppleSingle files onto disk images containing DOS 3.3 as well as ProDOS 8.

## 3. Memory layout

In the standard setup, cc65 generated programs use the memory from $803 to $95FF, so 35.5 KB of RAM are available.

Special locations:

Stack

  The C runtime stack is located at HIMEM and grows downwards, regardless of how your linker config file is setup.

Heap

  The C heap is located at the end of the program and grows towards the C runtime stack.

While running `main()` the Language Card bank 2 is enabled for read access. However while running module constructors/destructors the Language Card is disabled.

Enabling the Language Card allows to use it as additional memory for cc65 generated code. However code is never automatically placed there. Rather code needs to be explicitly placed in the Language Card either per file by compiling with `--code-name LC` or per function by enclosing in `#pragma code-name (push, "LC")` and `#pragma code-name (pop)`. In either case the cc65 runtime system takes care of actually moving the code into the Language Card.

The amount of memory available in the Language Card for generated code depends on the linker configuration parameters. There are several usefull settings:

LC address: $D400, LC size: $C00

  For plain vanilla ProDOS 8 which doesn't actually use the Language Card bank 2 memory from $D400 to $DFFF. This is the default setting.

LC address: $D000, LC size: $1000

  For ProDOS 8 together with the function `rebootafterexit()`. If a program doesn't quit to the ProDOS 8 dispatcher but rather reboots the machine after exit then a plain vanilla ProDOS 8 doesn't make use of the Language Card bank 2 at all.

LC address: $D000, LC size: $3000

  For plain vanilla DOS 3.3 which doesn't make use of the Language Card at all.

## 4. Linker configurations

The ld65 linker comes with a default config file for the Apple ][, which is used via `-t apple2`. The apple2 package comes with additional secondary linker config files, which are used via `-t apple2 -C <configfile>`.

## 4.1 default config file (`apple2.cfg`)

Default configuration for a binary program.

Parameters:

`STARTADDRESS:` Program start address

  Default: $803. Use `-S <addr>` to set a different start address.

`__EXEHDR__:` AppleSingle executable file header

  Default: Yes. Use `-D __EXEHDR__=0` to omit the AppleSingle header.

`__STACKSIZE__:` C runtime stack size

  Default: $800. Use `-D __STACKSIZE__=<size>` to set a different stack size.

`__HIMEM__:` Highest usable memory address presumed at link time

  Default: $9600. Use `-D __HIMEM__=<addr>` to set a different highest usable address.

`__LCADDR__:` Address of code in the Language Card

  Default: $D400. Use `-D __LCADDR__=<addr>` to set a different code address.

`__LCSIZE__:` Size of code in the Language Card

  Default: $C00. Use `-D __LCSIZE__=<size>` to set a different code size.

## 4.2 `apple2-system.cfg`

Configuration for a system program running on ProDOS 8 and using the memory from $2000 to $BEFF.

Parameters:

`__EXEHDR__:` AppleSingle executable file header

  Default: Yes. Use `-D __EXEHDR__=0` to omit the AppleSingle header.

`__STACKSIZE__:` C runtime stack size

  Default: $800. Use `-D __STACKSIZE__=<size>` to set a different stack size.

`__LCADDR__:` Address of code in the Language Card

  Default: $D400. Use `-D __LCADDR__=<addr>` to set a different code address.

`__LCSIZE__:` Size of code in the Language Card

  Default: $C00. Use `-D __LCSIZE__=<size>` to set a different code size.

## 4.3 `apple2-hgr.cfg`

Configuration for a program including a hires page. See `testcode/lib/apple/hgrtest.c` for an example of such a program.

Parameters:

`STARTADDRESS:` Program start address

  Default: $803. Use `-S <addr>` to set a different start address.

`__EXEHDR__:` AppleSingle executable file header

  Default: Yes. Use `-D __EXEHDR__=0` to omit the AppleSingle header.

`__STACKSIZE__:` C runtime stack size

  Default: $800. Use `-D __STACKSIZE__=<size>` to set a different stack size.

`__HIMEM__:` Highest usable memory address presumed at link time

  Default: $9600. Use `-D __HIMEM__=<addr>` to set a different highest usable address.

`__LCADDR__:` Address of code in the Language Card

  Default: $D400. Use `-D __LCADDR__=<addr>` to set a different code address.

`__LCSIZE__:` Size of code in the Language Card

  Default: $C00. Use `-D __LCSIZE__=<size>` to set a different code size.

## 4.4 `apple2-overlay.cfg`

Configuration for an overlay program with up to nine overlays. The overlay files don't include the AppleSingle header. See `samples/overlaydemo.c` for more information on overlays.

Parameters:

`STARTADDRESS:` Program start address

  Default: $803. Use `-S <addr>` to set a different start address.

`__EXEHDR__:` AppleSingle executable file header

  Default: Yes. Use `-D __EXEHDR__=0` to omit the AppleSingle header.

`__STACKSIZE__:` C runtime stack size

  Default: $800. Use `-D __STACKSIZE__=<size>` to set a different stack size.

`__HIMEM__:` Highest usable memory address presumed at link time

  Default: $9600. Use `-D __HIMEM__=<addr>` to set a different highest usable address.

`__LCADDR__:` Address of code in the Language Card

  Default: $D400. Use `-D __LCADDR__=<addr>` to set a different code address.

`__LCSIZE__:` Size of code in the Language Card

  Default: $C00. Use `-D __LCSIZE__=<size>` to set a different code size.

`__OVERLAYSIZE__:` Size of code in the overlays

  Default: $1000. Use `-D __OVERLAYSIZE__=<size>` to set a different code size.

## 4.5 `apple2-asm.cfg`

Configuration for an assembler program that doesn't need a special setup.

Parameters:

`STARTADDRESS:` Program start address

  Default: $803. Use `-S <addr>` to set a different start address.

`__EXEHDR__:` AppleSingle executable file header

  Default: No. Use `-u __EXEHDR__ apple2.lib` to add the AppleSingle header.

## 5. ProDOS 8 system programs

ProDOS 8 system programs are always loaded to the start address $2000. For cc65 programs this means that the 6 KB from $800 to $2000 are by default unused. There are however several options to make use of that memory range.

## 5.1 LOADER.SYSTEM

The easiest (and for really large programs in fact the only) way to have a cc65 program use the memory from $800 to $2000 is to link it as binary (as opposed to system) program using the default linker configuration apple2.cfg with `__HIMEM__` set to $BF00 and load it with the LOADER.SYSTEM utility. The program then works like a system program (i.e. quits to the ProDOS dispatcher).

Using LOADER.SYSTEM is as simple as copying it to the ProDOS 8 directory of the program to load under name <program>.SYSTEM as a system program. For example the program `MYPROG` is loaded by `MYPROG.SYSTEM`. The right AppleCommander option to put LOADER.SYSTEM on a ProDOS 8 disk image is `-p`.

## 5.2 Heap

If the cc65 program can be successfully linked as system program using the linker configuration apple2-system.cfg, but uses the heap either explicitly or implicitly (i.e. by loading a driver) then the memory from $800 to $2000 can be added to the heap by calling `_heapadd ((void *) 0x0800, 0x1800);` at the beginning of `main()`.

## 5.3 ProDOS 8 I/O buffers

ProDOS 8 requires for every open file a page-aligned 1 KB I/O buffer. By default these buffers are allocated by the cc65 runtime system on the heap using `posix_memalign()`. While this is generally the best solution it means quite some overhead for (especially rather small) cc65 programs which do open files but don't make use of the heap otherwise.

The apple2 package comes with the alternative ProDOS 8 I/O buffer allocation module `apple2-iobuf-0800.o` which uses the memory between $800 and the program start address for the 1 KB I/O buffers. For system programs (with start address $2000) this results in up to 6 I/O buffers and thus up to 6 concurrently open files.

While using `_heapadd()` as described in the section above together with the default I/O buffer allocation basically yields the same placement of I/O buffers in memory the primary benefit of `apple2-iobuf-0800.o` is a reduction in code size - and thus program file size - of more than 1400 bytes.

Using `apple2-iobuf-0800.o` is as simple as placing it on the linker command line like this:

> `

>     cl65 -t apple2 -C apple2-system.cfg myprog.c apple2-iobuf-0800.o

> `

## 6. Platform specific header files

Programs containing Apple ][ specific code may use the `apple2.h` header file.

## 6.1 Apple ][ specific functions

The functions listed below are special for the Apple ][. See the function reference for declaration and usage.

- _auxtype
- _dos_type
- _filetype
- get_ostype
- rebootafterexit
- ser_apple2_slot
- tgi_apple2_mix

## 6.2 Hardware access

There's currently no support for direct hardware access. This does not mean you cannot do it, it just means that there's no help.

## 7. Loadable drivers

The names in the parentheses denote the symbols to be used for static linking of the drivers.

## 7.1 Graphics drivers

`a2.lo.tgi (a2_lo_tgi)`

  This driver features a resolution of 40×48 with 16 colors.

  The function `tgi_apple2_mix()` allows to activate 4 lines of text. The function clears the corresponding area at the bottom of the screen.

`a2.hi.tgi (a2_hi_tgi)`

  This driver features a resolution of 280×192 with 8 colors and two hires pages. Note that programs using this driver will have to be linked with `-S $4000` to reserve the first hires page or with `-S $6000` to reserve both hires pages.

  The function `tgi_apple2_mix()` allows to activate 4 lines of text. The function doesn't clear the corresponding area at the bottom of the screen.

  In memory constrained situations the memory from $803 to $1FFF can be made available to a program by calling `_heapadd ((void *) 0x0803, 0x17FD);` at the beginning of `main()`. Doing so is beneficial even if the program doesn't use the the heap explicitly because loading the driver (and in fact already opening the driver file) uses the heap implicitly.

## 7.2 Extended memory drivers

`a2.auxmem.emd (a2_auxmem_emd)`

  Gives access to 47.5 KB RAM (190 pages of 256 bytes each) on an Extended 80-Column Text Card.

  Note that this driver doesn't check for the actual existence of the memory and that it doesn't check for ProDOS 8 RAM disk content!

## 7.3 Joystick drivers

`a2.stdjoy.joy (a2_stdjoy_joy)`

  Supports up to two standard analog joysticks connected to the game port of the Apple ][.

## 7.4 Mouse drivers

`a2.stdmou.mou (a2_stdmou_mou)`

  Driver for the AppleMouse II Card. Searches all Apple II slots for an AppleMouse II Card compatible firmware. The default bounding box is [0..279,0..191].

  Programs using this driver will have to be linked with `-S $4000` to reserve the first hires page if they are intended to run on an Apple ][ (in contrast to an Apple //e) because the AppleMouse II Card firmware writes to the hires page when initializing on that machine.

  Note that the Apple ][ default mouse callbacks support text mode only.

## 7.5 RS232 device drivers

`a2.ssc.ser (a2_ssc_ser)`

  Driver for the Apple II Super Serial Card. Supports up to 19200 baud, hardware flow control (RTS/CTS) and interrupt driven receives. Note that because of the peculiarities of the 6551 chip transmits are not interrupt driven, and the transceiver blocks if the receiver asserts flow control because of a full buffer.

  The driver defaults to slot 2. Call `ser_apple2_slot()` prior to `ser_open()` in order to select a different slot. `ser_apple2_slot()` succeeds for all Apple II slots, but `ser_open()` fails with `SER_ERR_NO_DEVICE` if there's no SSC firmware found in the selected slot.

## 8. Limitations

## 8.1 DOS 3.3

Although the standard binaries generated by the linker for the Apple ][ generally run both on DOS 3.3 (with Applesoft BASIC) and on ProDOS 8 (with BASIC.SYSTEM) there are some limitations for DOS 3.3:

Disk file I/O

  There's no disk file I/O support. Any attempt to use it yields an error with `errno` set to `ENOSYS`. This implicitly means that loadable drivers are in general not functional as they depend on disk file I/O. Therefore the statically linked drivers have to be used instead.

Interrupts

  There's no `interruptor` support. Any attempt to use it yields the message 'FAILED TO ALLOC INTERRUPT' on program startup. This implicitly means that mouse and RS232 device drivers are not functional as they depend on interrupts.

## 8.2 Direct console I/O

The Apple ][ has no color text mode. Therefore the functions `textcolor()`, `bgcolor()` and `bordercolor()` have no effect.

## 8.3 Random number generator

The random number seed is generated from the time the program waits for user input. Therefore it is necessary to wait for at least one user keypress either via Standard I/O or via Direct console I/O before initializing the pseudo random number generator.

## 8.4 Realtime clock

There are several types of realtime clocks. It's not desirable to have specific code for all of them. As ProDOS 8 supports file timestamps, realtime clock owners usually use ProDOS 8 drivers for their realtime clock. Those drivers read the realtime clock and write the result to the date/time location in RAM ($BF90 to $BF93). ProDOS 8 reads the date/time from that RAM location. If there's no realtime clock the RAM location keeps containing zeros. ProDOS 8 uses those zeros as timestamps and the files show up in a directory as `<NO DATE>`.

There's no common interface to set realtime clocks so if a realtme clock IS present there's just nothing to do. However, if there's NO realtime clock present, the user might very well be interested to "manually" set the RAM location in order to have timestamps. But he surely doesn't want to manually set the RAM location over and over again. Rather he wants to set it just once after booting ProDOS 8.

From that perspective it makes most sense to not set both the date and the time but rather only set the date and have the time just stay zero. Then files show up in a directory as `DD-MON-YY 0:00`.

So `clock_settime()` checks if a realtime clock is active. If it is then `clock_settime()` fails with `ERANGE`. Otherwise `clock_settime()` sets the date - and completely ignores the time provided as parameter.

`clock_getres()` too checks if a realtime clock is active. If it is then `clock_getres()` returns a time resolution of one minute. Otherwise `clock_getres()` presumes that the only one who sets the RAM location is `clock_settime()` and therefore returns a time resolution of one day.

## 9. Other hints

## 9.1 Passing arguments to the program

Command line arguments can be passed to `main()` after BLOAD. Since this is not supported by BASIC, the following syntax was chosen:

> `

>     ]CALL2051:REM ARG1 " ARG2 IS QUOTED" ARG3 "" ARG5

> `

1. Arguments are separated by spaces.
2. Arguments may be quoted.
3. Leading and trailing spaces around an argument are ignored. Spaces within a quoted argument are allowed.
4. The first argument passed to `main` is the program name.
5. A maximum number of 10 arguments (including the program name) are supported.

## 9.2 Interrupts

The runtime for the Apple ][ uses routines marked as `.INTERRUPTOR` for ProDOS 8 interrupt handlers. Such routines must be written as simple machine language subroutines and will be called automatically by the interrupt handler code when they are linked into a program. See the discussion of the `.CONDES` feature in the assembler manual.

## 9.3 DIO

Drive ID

  The function dio_open() has the single parameter `device` to identify the device to be opened. Therefore an Apple II slot and drive pair is mapped to that `device` according to the formula

  > `device = slot + (drive - 1) * 8`

  so that for example slot 6 drive 2 is mapped to `device` 14.

Sector count

  The function dio_query_sectcount() returns the correct sector count for all ProDOS 8 disks. However for any non-ProDOS 8 disk it simply always returns 280 (which is only correct for a 140 KB disk). This condition is indicated by the `_oserror` value 82.

## 9.4 Specifying file types for fopen

Explanation of File Types

  ProDOS associates a file type and an auxiliary type with each file. These type specifications are separate from the file's name, unlike Windows which uses the file name's suffix (a.k.a. extension) to specify the file type. For example, `.exe`, `.doc`, or `.bat`. The ProDOS low-level Machine-Language Interface (MLI) functions for creating and opening files require these types to be specified. And if they don't match with the file being opened, the operation may fail.

  In contrast, the ISO C function `fopen()` and the POSIX function `open()` have no parameter to specify either a file type or an auxiliary type. Therefore, some additional mechanism for specifying the file types is needed.

Specifying the File Type and Auxiliary Type

  There are two global variables provided that allow the file type and auxiliary type to be specified before a call to `fopen()` or `open()`. They are defined in `apple2_filetype.h`:

  > `

  >       extern unsigned char _filetype;  /* Default: PRODOS_T_BIN */
  >       extern unsigned int _auxtype;    /* Default: 0            */

  > `

  The header file `apple2_filetype.h` also defines many values that can be used to set these variables. It is included in `apple2.h`, which is in turn included in `apple2enh.h`. So it isn't necessary to include it directly. Just include one of `apple2.h` or `apple2enh.h`.

Example

  A text file cannot be created with just the standard C functions because they default to the binary type `PRODOS_T_BIN`. The `_filetype` variable must be set to `PRODOS_T_TXT` to create a text file.

  For a text file, `_auxtype` specifies the record length. A zero record length text file is referred to as a sequential text file. This is equivalent to text files on other operating systems, except that the line terminator is a carriage return instead of a line-feed (Linux/BSD/MacOS) or carriage return, line-feed pair (Windows).

  The "sequential" text file terminology is in contrast to a "random-access" text file which would have a fixed-length, non-zero record length, so that the file position of any individual record can be calculated.

  For this example, the `_auxtype` does not need to be set because it defaults to the desired value, which is zero. To be more explicit, `_auxtype` can also be set to `PRODOS_AUX_T_TXT_SEQ` which is defined as zero.

  > `

  >         #include <stdio.h>
  >         #include <string.h>
  >         #include <errno.h>
  >         #include <apple2.h>

  >         void main(void)
  >         {
  >             FILE *out;
  >             char *name = "MY.FAVS";

  >             /*-----------------------------*/

  >             _filetype = PRODOS_T_TXT;
  >             _auxtype  = PRODOS_AUX_T_TXT_SEQ;

  >             /*-----------------------------*/

  >             if ((out = fopen(name, "w")) != NULL) {
  >                 fputs("Jorah Mormont\r", out);
  >                 fputs("Brienne of Tarth\r", out);
  >                 fputs("Daenerys Targaryen\r", out);
  >                 fputs("Sandor Clegane\r", out);
  >                 if (fclose(out) == EOF) {
  >                     fprintf(stderr, "fclose failed for %s: %s", name, strerror(errno));
  >                 }
  >             }
  >             else {
  >                 fprintf(stderr, "fopen failed for %s: %s", name, strerror(errno));
  >             }
  >         }

  > `

## 10. License

This software is provided 'as-is', without any expressed or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.

Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
3. This notice may not be removed or altered from any source distribution.