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261 lines
7.5 KiB
Plaintext
261 lines
7.5 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>Commodore Plus/4 specific information for cc65
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<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">
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<date>2014-04-12
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<abstract>
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An overview over the Plus/4 runtime system as it is implemented for the cc65 C
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compiler.
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</abstract>
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<!-- Table of contents -->
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<toc>
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<!-- Begin the document -->
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<sect>Overview<p>
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This file contains an overview of the Plus/4 runtime system as it comes with the
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cc65 C compiler. It describes the memory layout, Plus/4 specific header files,
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available drivers, and any pitfalls specific to that platform.
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Please note that Plus/4 specific functions are just mentioned here, they are
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described in detail in the separate <url url="funcref.html" name="function
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reference">. Even functions marked as "platform dependent" may be available on
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more than one platform. Please see the function reference for more
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information.
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Since the Plus/4 and the Commodore 16/116 are almost identical (the latter are
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missing the 6551 ACIA and do only have 16KB of memory), the <url
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url="c16.html" name="C16 documentation"> is also worth a look. The difference
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between both cc65 targets is that the Plus/4 runtime uses banking to support
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full 64K RAM, while the C16 does not use banking and supports up to 32K RAM.
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Because banking is not needed, most C16 programs will be somewhat smaller than
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the same program compiled for the Plus/4. However, programs compiled for the
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C16 will always run on the Plus/4, while the reverse is not necessarily true.
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<sect>Binary format<p>
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The standard binary output format generated by the linker for the Plus/4
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target is a machine language program with a one line BASIC stub, which calls
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the machine language part via SYS. This means that a program can be loaded as
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BASIC program and started with RUN. It is of course possible to change this
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behaviour by using a modified startup file and linker config.
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<sect>Memory layout<p>
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cc65 generated programs with the default setup run with the kernal and basic
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banked out. This gives a usable memory range of $1000 - $FD00.
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Having the kernal and basic ROMs banked out means, that no ROM entry points
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may be called directly from user code.
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Special locations:
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<descrip>
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<tag/Text screen/
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The text screen is located at $C00 (as in the standard setup).
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<tag/Color RAM/
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The color RAM is located at $800 (standard location).
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<tag/Stack/
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The C runtime stack is located at $FCFF and growing downwards.
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<tag/Heap/
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The C heap is located at the end of the program and grows towards the C
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runtime stack.
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</descrip><p>
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<sect>Platform specific header files<p>
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Programs containing Plus/4 specific code may use the <tt/plus4.h/ or <tt/cbm.h/
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header files. Using the later may be an option when writing code for more than
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one CBM platform, since it includes <tt/plus4.h/ and declares several functions
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common to all CBM platforms.
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Please note that most of the header file declarations from the <tt/plus4.h/
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header file are shared between the C16 and Plus/4 configurations. For this
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reason, most of it is located in a common header file named <tt/cbm264.h/.
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<sect1>Plus/4 specific functions<p>
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There are currently no special Plus/4 functions.
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<sect1>CBM specific functions<p>
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Some functions are available for all (or at least most) of the Commodore
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machines. See the <url url="funcref.html" name="function reference"> for
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declaration and usage.
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<itemize>
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<item>cbm_close
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<item>cbm_closedir
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<item>cbm_k_setlfs
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<item>cbm_k_setnam
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<item>cbm_k_load
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<item>cbm_k_save
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<item>cbm_k_open
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<item>cbm_k_close
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<item>cbm_k_readst
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<item>cbm_k_chkin
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<item>cbm_k_ckout
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<item>cbm_k_basin
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<item>cbm_k_bsout
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<item>cbm_k_clrch
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<item>cbm_load
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<item>cbm_open
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<item>cbm_opendir
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<item>cbm_read
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<item>cbm_readdir
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<item>cbm_save
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<item>cbm_write
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<item>get_tv
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</itemize>
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<sect1>Hardware access<p>
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The following pseudo variables declared in the <tt/plus4.h/ header file do
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allow access to hardware located in the address space. Some variables are
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structures, accessing the struct fields will access the chip registers.
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<descrip>
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<tag><tt/TED/</tag>
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The <tt/TED/ structure allows access to the TED chip. See the
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<tt/_ted.h/ header file located in the include directory for the
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declaration of the structure.
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<tag><tt/COLOR_RAM/</tag>
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A character array that mirrors the color RAM of the Plus/4 at $0800.
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</descrip><p>
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<sect>Loadable drivers<p>
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The names in the parentheses denote the symbols to be used for static linking of the drivers.
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<sect1>Graphics drivers<p>
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No graphics drivers are currently available for the Plus/4.
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<sect1>Extended memory drivers<p>
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No extended memory drivers are currently available for the Plus/4.
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<sect1>Joystick drivers<p>
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<descrip>
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<tag><tt/plus4-stdjoy.joy (plus4_stdjoy_joy)/</tag>
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Supports up to two joysticks connected to the standard joysticks port of
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the Plus/4.
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</descrip><p>
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<sect1>Mouse drivers<p>
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No mouse drivers are currently available for the Plus/4.
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<sect1>RS232 device drivers<p>
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<descrip>
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<tag><tt/plus4-stdser.ser (plus4_stdser_ser)/</tag>
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Driver for the 6551 ACIA chip built into the Plus/4. Supports up to 19200
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baud, hardware flow control (RTS/CTS) and interrupt driven receives. Note
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that because of the peculiarities of the 6551 chip transmits are not
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interrupt driven, and the transceiver blocks if the receiver asserts flow
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control because of a full buffer.
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You need an adapter to use the builtin port, since the output levels
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available at the user port don't follow the RS232 standard.
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</descrip><p>
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<sect>Limitations<p>
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<sect>Other hints<p>
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<sect1>Passing arguments to the program<p>
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Command line arguments can be passed to <tt/main()/. Since this is not
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supported by BASIC, the following syntax was chosen:
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<tscreen><verb>
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RUN:REM ARG1 " ARG2 IS QUOTED" ARG3 "" ARG5
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</verb></tscreen>
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<enum>
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<item>Arguments are separated by spaces.
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<item>Arguments may be quoted.
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<item>Leading and trailing spaces around an argument are ignored. Spaces within
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a quoted argument are allowed.
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<item>The first argument passed to <tt/main/ is the program name.
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<item>A maximum number of 10 arguments (including the program name) are
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supported.
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</enum>
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<sect1>Program return code<p>
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The program return code (low byte) is passed back to BASIC by use of the
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<tt/ST/ variable.
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<sect1>Interrupts<p>
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The runtime for the Plus/4 uses routines marked as <tt/.INTERRUPTOR/ for
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interrupt handlers. Such routines must be written as simple machine language
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subroutines and will be called automatically by the interrupt handler code
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when they are linked into a program. See the discussion of the <tt/.CONDES/
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feature in the <url url="ca65.html" name="assembler manual">.
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<sect>License<p>
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This software is provided 'as-is', without any expressed or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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<enum>
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<item> The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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<item> Altered source versions must be plainly marked as such, and must not
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be misrepresented as being the original software.
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<item> This notice may not be removed or altered from any source
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distribution.
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</enum>
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</article>
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