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cc65 - a freeware C compiler for 6502 based systems
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Sidney Cadot bad2f54f75 Fix memory access order of the JSR instruction. 
The obvious way to implement JSR for the 6502 is to (a) read the target address,
and then (b) push the return address minus one. Or do (b) first, then (a).

However, there is a non-obvious case where this conflicts with the actual order
of operations that the 6502 does, which is:

(a) Load the LSB of the target address.
(b) Push the MSB of the return address, minus one.
(c) Push the LSB of the return address, minus one.
(d) Load the MSB of the target address.

This can make a difference in a pretty esoteric case, if the JSR target is located,
wholly or in part, inside the stack page (!). This won't happen in normal code
but it can happen in specifically constructed examples.

To deal with this, we load the LSB and MSB of the target address separately, with
the pushing of the return address sandwiched in between, to mimic the order of the
bus operations on a real 6502.
2024-12-19 22:35:15 +01:00
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asminc Changed 0x hex values to % binary values 2024-11-09 11:45:41 +01:00
cfg
doc Merge pull request #2558 from polluks/cpp 2024-12-15 23:02:35 +01:00
include Rename dir_file_count to dir_entry_count 2024-11-15 19:25:40 +01:00
libsrc Merge pull request #2558 from polluks/cpp 2024-12-15 23:02:35 +01:00
samples Update sieve.c 2024-12-09 18:26:00 +01:00
src Fix memory access order of the JSR instruction. 2024-12-19 22:35:15 +01:00
targettest
test Merge pull request #2522 from kugelfuhr/kugelfuhr/code-optimizations 2024-10-05 15:03:46 +02:00
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README.md

The cc65 cross-compiler suite

cc65 is a complete cross-development package for 65(C)02 systems, including a powerful macro assembler, a C compiler, linker, archiver, simulator and several other tools. cc65 has C and runtime library support for many of the old 6502 machines. For details look at the cc65 web site:

Company / People Machine / Environment
Apple Apple II
Apple IIe enhanced
Atari Atari 400/800
Atari 2600
Atari 5200
Atari 7800
Atari XL
Lynx
Tangerine Oric Atmos
Eureka Oric Telestrat
Acorn BBC series
Commodore C128
C16
C64
CBM 510/610
PET
Plus/4
VIC-20
VTech CreatiVision
Commander X16 Community Commander X16
Bit Corporation Gamate
Berkeley Softworks GEOS (Apple/CBM)
LUnix Team LUnix (C64)
Nintendo Nintendo Entertainment System (NES)
Ohio Scientific OSI C1P
MOS Technology, Inc. KIM-1
NEC PC Engine (PCE)
Dr. Jozo Dujmović Picocomputer (RP6502)
Watara Watura/QuickShot Supervision
Synertek SYM-1

A generic configuration to adapt cc65 to new targets is also around.

People

cc65 is originally based on the "Small C" compiler by Ron Cain and enhanced by James E. Hendrix.

Project founders

  • John R. Dunning: original implementation of the C compiler and runtime library, Atari hosted.
  • Ullrich von Bassewitz:
    • moved Dunning's code to modern systems,
    • rewrote most parts of the compiler,
    • rewrote all of the runtime library.

Core team members

External contributors

(The above list is incomplete, if you feel left out - please speak up or add yourself in a PR)

For a complete list look at the full team list or the list of all contributors.

Contact

For general discussion, questions, etc subscribe to the mailing list or use the github discussions.

Some of us may also be around on IRC #cc65 on libera.chat.

Documentation

  • The main Documentation for users and developers.
  • Info on Contributing to the CC65 project. Please read this before working on something you want to contribute, and before reporting bugs.
  • The Wiki contains some extra info that does not fit into the regular documentation.

Downloads

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