1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
|
f65 - "fake 6502" porting layer
This is a set of C macros that implements most of the 6502 assembly
language instructions, plus a perl script to convert 6502 assembly
source to C code that calls the macros. You can use it to assist in
porting 6502 assembly routines to C, using either the original asm
source, or a disassembly created with da65.
What's implemented: 64K of memory. The A/X/Y/S registers. The carry,
zero, and negative flags. Most arithmetic and logic instructions. The
stack. Conditional branches and absolute jumps are implemented as C
goto's. JSR is implemented as a real C function call, and RTS is a
real C return. Labels in the assembly source become C labels (aka goto
targets). Equates in the asm source become C variables.
What's not implemented: The D flag, and decimal mode in general. The
V flag, and branches based on it. The I and B flags. Interrupts
and the RTI instruction. The Program Counter (though branches, JMP,
JSR, and RTS are implemented without it). ROM routines (including
I/O). Indirect JMP. The "CPU bug" that causes e.g. 'LDA ($FF),y' to
take its high byte from $00 rather than $100. (zeropage, x) addressing
mode.
I wrote this specifically to port the decompression algorithm from
UnAlf 1.4. Instructions not used by UnAlf probably aren't implemented,
or if they are, they're untested.
The perl script doesn't magically convert a whole 6502 program to C
source. You'll have to figure out which parts of the 6502 program are
subroutines, and put them in their own C functions. Any data (.byte,
.word, etc) won't be in the C program. Anything that does I/O must be
rewritten in C.
|
