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}

sub _rts {
  return
     'my ($lo, $hi); '
   . _pop( '$lo' )
   . _pop( '$hi' )
   . '$pc = ($lo | ($hi << 8)) + 1;' . "\n";
}

1;
__END__

=head1 NAME

Acme::6502 - Pure Perl 65C02 simulator.

=head1 VERSION

This document describes Acme::6502 version 0.76

=head1 SYNOPSIS

    use Acme::6502;
    
    my $cpu = Acme::6502->new();
    
    # Set start address
    $cpu->set_pc(0x8000);
    
    # Load ROM image
    $cpu->load_rom('myrom.rom', 0x8000);
    
    # Run for 1,000,000 instructions then return
    $cpu->run(1_000_000);
  
=head1 DESCRIPTION

Imagine the nightmare scenario: your boss tells you about a legacy
system you have to support. How bad could it be? COBOL? Fortran? Worse:
it's an embedded 6502 system run by a family of squirrels (see Dilberts
passim). Fortunately there's a pure Perl 6502 emulator that works so
well the squirrels will never know the difference.

=head1 INTERFACE 

=over

=item C<new>

Create a new 6502 CPU.

=item C<call_os( $vec_number )>

Subclass to provide OS entry points. OS vectors are installed by calling
C<make_vector>. When the vector is called C<call_os()> will be called
with the vector number.

=item C<get_a()>

Read the current value of the processor A register (accumulator).

=item C<get_p()>

Read the current value of the processor status register.

=item C<get_pc()>

Read the current value of the program counter.

=item C<get_s()>

Read the current value of the stack pointer.

=item C<get_x()>

Read the current value of the processor X index register.

=item C<get_y()>

Read the current value of the processor X index register.

=item C<get_xy()>

Read the value of X and Y as a sixteen bit number. X forms the lower 8
bits of the value and Y forms the upper 8 bits.

=item C<get_state()>

Returns an array containing the values of the A, X, Y, S, P and SP.

=item C<set_a( $value )>

Set the value of the processor A register (accumulator).

=item C<set_p( $value )>

Set the value of the processor status register.

=item C<set_pc( $value )>

Set the value of the program counter.

=item C<set_s( $value )>

Set the value of the stack pointer.

=item C<set_x( $value )>

Set the value of the X index register.

=item C<set_y( $value )>

Set the value of the Y index register.

=item C<set_xy( $value )>

Set the value of the X and Y registers to the specified sixteen bit
number. X gets the lower 8 bits, Y gets the upper 8 bits.

=item C<set_jumptab( $addr )>

Set the address of the block of memory that will be used to hold the
thunk blocks that correspond with vectored OS entry points. Each thunk
takes four bytes.

=item C<load_rom( $filename, $addr )>

Load a ROM image at the specified address.

=item C<make_vector( $jmp_addr, $vec_addr, $vec_number )>

Make a vectored entry point for an emulated OS. C<$jmp_addr> is the
address where an indirect JMP instruction (6C) will be placed,
C<$vec_addr> is the address of the vector and C<$vec_number> will be
passed to C<call_os> when the OS call is made.

=item C<poke_code( $addr, @bytes )>

Poke code directly at the specified address.

=item C<read_8( $addr )>

Read a byte at the specified address.

=item C<read_16( $addr )>

Read a sixteen bit (low, high) word at the specified address.

=item C<read_32( $addr )>

Read a 32 bit word at the specified address.

=item C<read_chunk( $start, $end )>

Read a chunk of data from C<$start> to C<$end> - 1 into a string.

=item C<read_str( $addr )>