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Merge pull request #2437 from bbbradsmith/sim65-examples 

provide simple examples for using sim65 with C and assembly code
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@ -115,37 +115,78 @@ PVExit ($01)
<sect>Creating a Test in C<p>
For a C test compiled and linked with <tt/--target sim6502/ the
For a C test linked with <tt/--target sim6502/ and the <tt/sim6502.lib/ library,
command line arguments to <tt/sim65/ will be passed to <tt/main/,
and the return value from <tt/main/ will become sim65's exit code.
The <tt/exit/ function may also be used to terminate with an exit code.
The <tt/stdlib.h/ <tt/exit/ function may also be used to terminate with an exit code.
Exit codes are limited to 8 bits.
Exit codes are limited to an unsigned 8 bit value. (E.g. returning -1 will give an exit code of 255.)
The standard C library high level file input and output is functional.
A sim65 application can be written like a command line application,
providing arguments to <tt/main/ and using the <tt/stdio.h/ interfaces.
providing command line arguments to <tt/main/ and using the <tt/stdio.h/ interfaces
to interact with the console or access files.
Internally, file input and output is provided at a lower level by
a set of built-in paravirtualization functions (<ref id="paravirt-internal" name="see below">).
a set of built-in paravirtualization functions (see <ref id="paravirt-internal" name="below">).
Example:
<tscreen><verb>
#include <stdio.h>
int main()
{
printf("Hello!\n");
return 5;
}
// Build and run:
// cl65 -t sim6502 -o example.prg example.c
// sim65 example.prg
// Build and run, separate steps:
// cc65 -t sim6502 -o example.s example.c
// ca65 -t sim6502 -o example.o example.s
// ld65 -t sim6502 -o example.prg example.o sim6502.lib
// sim65 example.prg
</verb></tscreen>
<sect>Creating a Test in Assembly<p>
Assembly tests may similarly be assembled and linked with
<tt/--target sim6502/ or <tt/--target sim65c02/.
Define and export <tt/_main/ as an entry point,
Though a C test may also link with assembly code,
a pure assembly test can also be created.
Link with <tt/--target sim6502/ or <tt/--target sim65c02/ and the corresponding library,
define and export <tt/_main/ as an entry point,
and the sim65 library provides two ways to return an 8-bit exit code:
<itemize>
<item>Return from <tt/_main/ with the exit code in <tt/A/.
<item><tt/jmp exit/ with the code in <tt/A/.
<item><tt/jmp exit/ with the code in <tt/A/. (<tt/.import exit/ from the sim65 library.)
</itemize>
The binary file has a 12 byte header:
Example:
<tscreen><verb>
.export _main
_main:
lda #5
rts
; Build and run:
; cl65 -t sim6502 -o example.prg example.s
; sim65 example.prg
; Build and run, separate steps:
; ca65 -t sim6502 -o example.o example.s
; ld65 -t sim6502 -o example.prg example.o sim6502.lib
; sim65 example.prg
</verb></tscreen>
Internally, the binary program file has a 12 byte header provided by the library:
<itemize>
@ -182,6 +223,9 @@ These use cc65 calling conventions, and are intended for use with the sim65 targ
<item><tt/IRQ/ and <tt/NMI/ events will not be generated, though <tt/BRK/
can be used if the IRQ vector at <tt/$FFFE/ is manually prepared by the test code.
<item>The <tt/sim6502/ or <tt/sim65c02/ targets provide a default configuration,
but if customization is needed <tt/sim6502.cfg/ or <tt/sim65c02.cfg/ might be used as a template.
</itemize>