A MOS 6502 Emulator intended to be used from within other programs. All opcodes, included the undocumented illegal opcodes are implemented.
Example Usage
from py65emu.cpu import CPU
from py65emu.mmu import MMU
f = open("program.rom", "rb") # Open your rom
# define your blocks of memory. Each tuple is
# (start_address, length, readOnly=True, value=None, valueOffset=0)
m = MMU([
(0x00, 0x200), # Create RAM with 512 bytes
(0x1000, 0x4000, True, f) # Create ROM starting at 0x1000 with your program.
])
# Create the CPU with the MMU and the starting program counter address
# You can also optionally pass in a value for stack_page, which defaults
# to 1, meaning the stack will be from 0x100-0x1ff. As far as I know this
# is true for all 6502s, but for instance in the 6507 used by the Atari
# 2600 it is in the zero page, stack_page=0.
c = CPU(mmu, 0x1000)
# Do this to execute one instruction
c.step()
# You can check the registers and memory values to determine what has changed
print(c.r.a) # A register
print(c.r.x) # X register
print(c.r.y) # Y register
print(c.r.s) # Stack Pointer
print(c.r.pc) # Program Counter
print(c.cc) # Print the number of cycles that passed during the last step.
# This number resets for each call to `.step()`
print(c.r.getFlag('C')) # Get the value of a flag from the flag register.
print(mmu.read(0xff)) # Read a value from memory
The full set of parameters for CPU is
mmu: An instance of MMU
pc: The starting address of the pc (program counter)
stack_page: The index of the page which contains the stack. The default for
a 6502 is page 1 (the stack from 0x0100-0x1ff) but in some varients the
stack page may be elsewhere.
magic: A value needed for the illegal opcodes, XAA. This value differs
between different versions, even of the same CPU. The default is 0xee.
And for MMU, the tuple values are
start : int
The starting address of the block of memory
length : int
The length of the block in bytes
readOnly: bool
Whether the block should be read only (such as ROM) (default False)
value : file pointer, binary or lint of unsigned integers
The intial value for the block of memory. Used for loading program
data. (Default None)
valueOffset : integer
Used when copying the above `value` into the block to offset the
location it is copied into. For example, to copy byte 0 in `value`
into location 1000 in the block, set valueOffest=1000. (Default 0)