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329 lines
10 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>Commodore 510 (aka P500) specific information for cc65
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<author>
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<url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">,<newline>
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<url url="mailto:polluks@sdf.lonestar.org" name="Stefan A. Haubenthal">,<newline>
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<url url="mailto:greg.king5@verizon.net" name="Greg King">
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<date>2014-04-25
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<abstract>
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An overview over the Commodore 510 runtime system as it is implemented for the
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cc65 C 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 CBM 510 runtime system as it comes with
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the cc65 C compiler. It describes the memory layout, CBM 510-specific header
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files, available drivers, and any pitfalls specific to that platform.
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Please note that CBM 510-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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In addition to the Commodore 510 (named P128 in the U.S.), no other
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machines are supported by this cc65 target.
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<sect>Binary format<p>
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The standard binary output format generated by the linker for the Commodore
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510 target is a machine language program with a one-line BASIC stub, which
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transfers control to the machine language running in bank 0. That means that a
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program can be loaded as a BASIC program, and started with RUN. It is, of course,
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possible to change that behaviour by using a modified startup file and linker
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config.
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<sect>Memory layout<p>
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cc65 generated programs for the Commodore 510 run in bank 0, the memory bank
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reserved for BASIC programs. Since there are no ROMs in this memory bank,
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kernal subroutines are either emulated or called by bank switching, which has
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the disadvantage of being slow compared to a direct call.
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The default memory configuration for the CBM 510 allocates all memory between
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$0002 and $FFF0 in bank 0 for the compiled program. Some space
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in low memory is lost, because a separate hardware stack is set up in page 1,
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and the kernal replacement functions need some more memory locations. A few
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more pages are lost in high memory, because the runtime sets up a copy of the
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character ROM, a text screen, and a CBM-compatible jump table at $FF81.
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The main startup code is located at $0400, so about 54K of the complete
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bank are actually usable for applications.
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Special locations:
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<descrip>
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<tag/Stack/
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The C runtime stack is located at $FEC2, and grows 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 CBM 510-specific code may use the <tt/cbm510.h/ or
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<tt/cbm.h/ header files. Using the later may be an option when writing code
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for more than one CBM platform, since it includes <tt/cbm510.h/, and declares
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several functions common to all CBM platforms.
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<sect1>CBM 510-specific functions<p>
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The functions listed below are special for the CBM 510. See the <url
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url="funcref.html" name="function reference"> for declaration and usage.
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<itemize>
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<item>peekbsys
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<item>peekwsys
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<item>pokebsys
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<item>pokewsys
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</itemize>
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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/cbm510.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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<em/Note:/ All I/O chips are located in the system bank (bank 15); and can
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therefore not be accessed like on other platforms. Please use one of the
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<tt/peekbsys/, <tt/peekwsys/, <tt/pokebsys/, and <tt/pokewsys/ functions to
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access the I/O chips. Direct reads and writes to the structures named below
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will <em>not</em> work!
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<descrip>
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<tag><tt/VIC/</tag>
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The <tt/VIC/ structure allows access to the VIC II (the graphics
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controller). See the <tt/_vic2.h/ header file located in the include
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directory for the declaration of the structure.
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<tag><tt/SID/</tag>
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The <tt/SID/ structure allows access to the SID (the sound interface
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device). See the <tt/_sid.h/ header file located in the include directory
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for the declaration of the structure.
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<tag><tt/ACIA/</tag>
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Access to the ACIA (the RS232 chip) is available via the <tt/ACIA/ variable.
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See the <tt/_6551.h/ header file located in the include directory for the
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declaration of the structure.
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<tag><tt/CIA/</tag>
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Access to the CIA chip is available via the <tt/CIA/ variable. See the
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<tt/_6526.h/ header file located in the include directory for the
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declaration of the structure.
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<tag><tt/TPI1, TPI2/</tag>
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The two 6525 triport chips may be accessed by using these variables. See the
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<tt/_6525.h/ header file located in the include directory for the
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declaration of the structure.
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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 Commodore 510.
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<sect1>Extended memory drivers<p>
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<descrip>
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<tag><tt/cbm510-ram.emd (cbm510_ram_emd)/</tag>
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A driver for the RAM in bank 1. Supports up to 255 pages with 256 bytes
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each.
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</descrip><p>
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<sect1>Joystick drivers<p>
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<descrip>
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<tag><tt/cbm510-std.joy (cbm510_std_joy)/</tag>
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Supports up to two standard joysticks connected to the joysticks ports of
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the Commodore 510.
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</descrip><p>
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<sect1>Mouse drivers<p>
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The default drivers, <tt/mouse_stddrv (mouse_static_stddrv)/, point to <tt/cbm510-joy.mou (cbm510_joy_mou)/.
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<descrip>
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<tag><tt/cbm510-joy.mou (cbm510_joy_mou)/</tag>
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Supports a mouse that is emulated by a standard joystick, e.g. 1350
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mouse, in joystick port #2 of the CBM510. That stick's fire button acts as
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the left mouse button. The fire button of a stick in joystick port #1 can
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act as the right mouse button.
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<tag><tt/cbm510-inkwl.mou (cbm510_inkwl_mou)/</tag>
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Supports the Inkwell Systems lightpens, connected to port #1 of the CBM510.
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It can read both the 170-C and one button of the 184-C pens. (It can
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read other lightpens and light-guns that send their button signal to the
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joystick left-button pin.)
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</descrip><p>
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<sect1>RS232 device drivers<p>
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<descrip>
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<tag><tt/cbm510-std.ser (cbm510_std_ser)/</tag>
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Driver for the 6551 ACIA chip built into the Commodore 510. Supports up to
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19200 BPS, hardware flow control (RTS/CTS), and interrupt-driven receives.
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Note 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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</descrip><p>
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<sect>Limitations<label id="limitations"><p>
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<sect1>Kernal and hardware access<p>
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Since the program runs in bank 0, and the kernal and all I/O chips are located
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in bank 15, calling ROM routines or accessing hardware needs special code. The
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cc65 runtime implements wrappers for all functions in the kernal jump table.
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While this simplifies things, it should be noted that the wrappers do have
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quite an impact on performance: A cross-bank call has an extra 300µs
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penalty added by the wrapper.
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<sect1>Interrupts<p>
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Compiled programs contain an interrupt handler that runs in the program bank.
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This has several advantages, one of them being performance (see cross-bank
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call overhead mentioned above). However, this introduces one problem:
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Interrupts are lost while the CPU executes code in the kernal bank. As a
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result, the clock may go wrong; and (worse), serial interrupts may get lost.
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Since the cc65 runtime does only call the kernal for disk I/O, this means that
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a program should not do file I/O while it depends on interrupts.
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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 that is not
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supported directly 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 (signed char) is passed back to BASIC by use of the
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<tt/ST/ variable.
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<sect1>Interrupt handlers<p>
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The runtime for the Commodore 510 uses routines marked as <tt/.INTERRUPTOR/
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for interrupt handlers. Such routines must be written as simple machine
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language subroutines and will be called automatically by the interrupt handler
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code when they are linked into a program. See the discussion of the
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<tt/.CONDES/ 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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