1 <!doctype linuxdoc system>
5 <title>Commodore 610 specific information for cc65
6 <author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
10 An overview over the Commodore 610 runtime system as it is implemented for the
14 <!-- Table of contents -->
17 <!-- Begin the document -->
21 This file contains an overview of the CBM 610 runtime system as it comes with
22 the cc65 C compiler. It describes the memory layout, CBM 610 specific header
23 files, available drivers, and any pitfalls specific to that platform.
25 Please note that CBM 610 specific functions are just mentioned here, they are
26 described in detail in the separate <htmlurl url="funcref.html" name="function
27 reference">. Even functions marked as "platform dependent" may be available on
28 more than one platform. Please see the function reference for more
31 In addition to the Commodore 610 (named B40 in the U.S.), several other
32 machines are supported by this cc65 target, since they have identical
33 hardware: The Commodore 620 and 630 (more memory, additional coprocessor
34 card), and the Commodore 710, 720 and 730 (same hardware in another case with
39 <sect>Binary format<p>
41 The standard binary output format generated by the linker for the CBM610
42 target is a machine language program with a short BASIC stub. This means that
43 a program can be loaded as BASIC program and started with RUN. It is of course
44 possible to change this behaviour by using a modified startup file and linker
48 <sect>Memory layout<p>
50 cc65 generated programs for the Commodore 610 run in bank 1, the memory bank
51 reserved for BASIC programs. Since there are no ROMs in this memory bank,
52 kernal subroutines are either emulated or called by bank switching, which has
53 the disadvantage of being slow compared to a direct call.
55 The default memory configuration for the CBM 610 allocates all memory between
56 $0002 and $FFF0 in bank 1 for the compiled program. Some space
57 in low memory is lost, because a separate hardware stack is set up in page 1,
58 and the kernal replacement functions need some more memory locations. A few
59 more bytes are lost in high memory, because the runtime sets up a CBM
60 compatible jump table at $FF81. The main startup code is located at
61 $0400, so about 63K of the complete bank are actually usable for
68 The C runtime stack is located at $FF81 and growing downwards.
71 The C heap is located at the end of the program and grows towards the C
77 <sect>Platform specific header files<p>
79 Programs containing CBM 610 specific code may use the <tt/cbm610.h/ or
80 <tt/cbm.h/ header files. Using the later may be an option when writing code
81 for more than one CBM platform, since it includes <tt/cbm610.h/ and declares
82 several functions common to all CBM platforms.
84 <sect1>CBM 610 specific functions<p>
86 The functions listed below are special for the CBM 610. See the <htmlurl
87 url="funcref.html" name="function reference"> for declaration and usage.
97 <sect1>CBM specific functions<p>
99 Some functions are available for all (or at least most) of the Commodore
100 machines. See the <htmlurl url="funcref.html" name="function reference"> for
101 declaration and usage.
131 <sect1>Hardware access<p>
133 The following pseudo variables declared in the <tt/cbm610.h/ header file do
134 allow access to hardware located in the address space. Some variables are
135 structures, accessing the struct fields will access the chip registers.
137 <bf>Note:</bf> All I/O chips are located in the system bank (bank 15) and can
138 therefore not be accessed like on other platforms. Please use one of the
139 <tt/peekbsys/, <tt/peekwsys/, <tt/pokebsys/ and <tt/pokewsys/ functions to
140 access the I/O chips. Direct reads and writes to the structures named below
141 will <em>not</em> work!
146 The <tt/CRTC/ structure allows access to the CRTC (the video controller).
147 See the <tt/_6545.h/ header file located in the include directory for the
148 declaration of the structure.
150 <tag><tt/SID/</tag> The <tt/SID/ structure allows access to the SID (the
151 sound interface device). See the <tt/_sid.h/ header file located in the
152 include directory for the declaration of the structure.
155 Access to the ACIA (the RS232 chip) is available via the <tt/ACIA/ variable.
156 See the <tt/_6551.h/ header file located in the include directory for the
157 declaration of the structure.
160 Access to the CIA chip is available via the <tt/CIA/ variable. See the
161 <tt/_6526.h/ header file located in the include directory for the
162 declaration of the structure.
164 <tag><tt/TPI1, TPI2/</tag>
165 The two 6525 triport chips may be accessed by using this variable. See the
166 <tt/_6525.h/ header file located in the include directory for the
167 declaration of the structure.
173 <sect>Loadable drivers<p>
176 <sect1>Graphics drivers<p>
178 No graphics drivers are currently available for the Commodore 610 (and since
179 the machine has no graphics capabilities, chances for a graphics driver aren't
183 <sect1>Extended memory drivers<p>
186 <tag><tt/cbm610-ram.emd/</tag>
187 A driver for the RAM in bank 2. Supports up to 255 pages with 256 bytes
192 <sect1>Joystick drivers<p>
194 The Commodore 610 is a business machine and doesn't have joystick ports. There
195 are no drivers for the non existing ports available.
199 <sect1>Mouse drivers<p>
201 Currently no drivers available (in fact, the API for loadable mouse drivers
205 <sect1>RS232 device drivers<p>
209 <tag><tt/cbm610-std.ser/</tag>
210 Driver for the 6551 ACIA chip built into the Commodore 610. Supports up to
211 19200 baud, hardware flow control (RTS/CTS) and interrupt driven receives.
212 Note that because of the peculiarities of the 6551 chip transmits are not
213 interrupt driven, and the transceiver blocks if the receiver asserts flow
214 control because of a full buffer.
219 <sect>Limitations<label id="limitations"><p>
222 <sect1>Kernal and hardware access<p>
224 Since the program runs in bank 1, and the kernal and all I/O chips are located
225 in bank 15, calling ROM routines or accessing hardware needs special code. The
226 cc65 runtime implements wrappers for all functions in the kernal jump table.
227 While this simplifies things, it should be noted that the wrappers do have
228 quite an impact on performance: A cross bank call has an extra 300µs
229 penalty added by the wrapper.
233 Compiled programs contain an interrupt handler that runs in the program bank.
234 This has several advantages, one of them being performance (see cross bank
235 call overhead mentioned above). However, this introduces one problem:
236 Interrupts are lost while the CPU executes code in the kernal bank. As a
237 result, the clock may go wrong and (worse) serial interrupts may get lost.
239 Since the cc65 runtime does only call the kernal for disk I/O, this means that
240 a program should not do file I/O while it depends on interrupts.
245 <sect1>Passing arguments to the program<p>
247 Command line argument passing is currently not supported for the Commodore
251 <sect1>Program return code<p>
253 The program return code (low byte) is passed back to BASIC by use of the
257 <sect1>Interrupt handlers<p>
259 The runtime for the Commodore 610 uses routines marked as <tt/.CONDES/ type 2
260 for interrupt handlers. Such routines must be written as simple machine
261 language subroutines and will be called automatically by the interrupt handler
262 code when they are linked into a program. See the discussion of the
263 <tt/.CONDES/ feature in the <htmlurl url="ca65.html" name="assembler manual">.
267 <sect>Bugs/Feedback<p>
269 If you have problems using the library, if you find any bugs, or if you're
270 doing something interesting with it, I would be glad to hear from you. Feel
271 free to contact me by email (<htmlurl url="mailto:uz@cc65.org"
272 name="uz@cc65.org">).
278 This software is provided 'as-is', without any expressed or implied
279 warranty. In no event will the authors be held liable for any damages
280 arising from the use of this software.
282 Permission is granted to anyone to use this software for any purpose,
283 including commercial applications, and to alter it and redistribute it
284 freely, subject to the following restrictions:
287 <item> The origin of this software must not be misrepresented; you must not
288 claim that you wrote the original software. If you use this software
289 in a product, an acknowledgment in the product documentation would be
290 appreciated but is not required.
291 <item> Altered source versions must be plainly marked as such, and must not
292 be misrepresented as being the original software.
293 <item> This notice may not be removed or altered from any source