mirror of
https://github.com/ekeeke/Genesis-Plus-GX.git
synced 2024-12-30 21:21:49 +01:00
316 lines
11 KiB
Plaintext
316 lines
11 KiB
Plaintext
MUSASHI
|
|
=======
|
|
|
|
Version 3.3
|
|
|
|
A portable Motorola M680x0 processor emulation engine.
|
|
Copyright 1998-2001 Karl Stenerud. All rights reserved.
|
|
|
|
|
|
|
|
INTRODUCTION:
|
|
------------
|
|
|
|
Musashi is a Motorola 68000, 68010, 68EC020, and 68020 emulator written in C.
|
|
This emulator was written with two goals in mind: portability and speed.
|
|
|
|
The emulator is written to ANSI C specifications with the exception that I use
|
|
inline functions. This is not compliant to the ANSI spec, but will be
|
|
compliant to the ANSI C9X spec.
|
|
|
|
It has been successfully running in the MAME project (www.mame.net) for over 2
|
|
years and so has had time to mature.
|
|
|
|
|
|
|
|
LICENSE AND COPYRIGHT:
|
|
---------------------
|
|
|
|
The Musashi M680x0 emulator is copyright 1998-2001 Karl Stenerud.
|
|
|
|
The source code included in this archive is provided AS-IS, free for any
|
|
non-commercial purpose.
|
|
|
|
If you build a program using this core, please give credit to the author.
|
|
|
|
If you wish to use this core in a commercial environment, please contact
|
|
the author to discuss commercial licensing.
|
|
|
|
|
|
|
|
AVAILABILITY:
|
|
------------
|
|
The latest version of this code can be obtained at:
|
|
http://kstenerud.cjb.net
|
|
|
|
|
|
|
|
CONTACTING THE AUTHOR:
|
|
---------------------
|
|
I can be reached at kstenerud@mame.net
|
|
|
|
|
|
|
|
BASIC CONFIGURATION:
|
|
-------------------
|
|
The basic configuration will give you a standard 68000 that has sufficient
|
|
functionality to work in a primitive environment.
|
|
|
|
This setup assumes that you only have 1 device interrupting it, that the
|
|
device will always request an autovectored interrupt, and it will always clear
|
|
the interrupt before the interrupt service routine finishes (but could
|
|
possibly re-assert the interrupt).
|
|
You will have only one address space, no tracing, and no instruction prefetch.
|
|
|
|
To implement the basic configuration:
|
|
|
|
- Open m68kconf.h and verify that the settings for INLINE and DECL_SPEC will
|
|
work with your compiler. (They are set for gcc)
|
|
|
|
- In your host program, implement the following functions:
|
|
unsigned int m68k_read_memory_8(unsigned int address);
|
|
unsigned int m68k_read_memory_16(unsigned int address);
|
|
unsigned int m68k_read_memory_32(unsigned int address);
|
|
void m68k_write_memory_8(unsigned int address, unsigned int value);
|
|
void m68k_write_memory_16(unsigned int address, unsigned int value);
|
|
void m68k_write_memory_32(unsigned int address, unsigned int value);
|
|
|
|
- In your host program, be sure to call m68k_pulse_reset() once before calling
|
|
any of the other functions as this initializes the core.
|
|
|
|
- Use m68k_execute() to execute instructions and m68k_set_irq() to cause an
|
|
interrupt.
|
|
|
|
|
|
|
|
ADDING PROPER INTERRUPT HANDLING:
|
|
--------------------------------
|
|
The interrupt handling in the basic configuration doesn't emulate the
|
|
interrupt acknowledge phase of the CPU and automatically clears an interrupt
|
|
request during interrupt processing.
|
|
While this works for most systems, you may need more accurate interrupt
|
|
handling.
|
|
|
|
To add proper interrupt handling:
|
|
|
|
- In m68kconf.h, set M68K_EMULATE_INT_ACK to OPT_SPECIFY_HANDLER
|
|
|
|
- In m68kconf.h, set M68K_INT_ACK_CALLBACK(A) to your interrupt acknowledge
|
|
routine
|
|
|
|
- Your interrupt acknowledge routine must return an interrupt vector,
|
|
M68K_INT_ACK_AUTOVECTOR, or M68K_INT_ACK_SPURIOUS. most m68k
|
|
implementations just use autovectored interrupts.
|
|
|
|
- When the interrupting device is satisfied, you must call m68k_set_irq(0) to
|
|
remove the interrupt request.
|
|
|
|
|
|
|
|
MULTIPLE INTERRUPTS:
|
|
-------------------
|
|
The above system will work if you have only one device interrupting the CPU,
|
|
but if you have more than one device, you must do a bit more.
|
|
|
|
To add multiple interrupts:
|
|
|
|
- You must make an interrupt arbitration device that will take the highest
|
|
priority interrupt and encode it onto the IRQ pins on the CPU.
|
|
|
|
- The interrupt arbitration device should use m68k_set_irq() to set the
|
|
highest pending interrupt, or 0 for no interrupts pending.
|
|
|
|
|
|
|
|
SEPARATE IMMEDIATE AND PC-RELATIVE READS:
|
|
----------------------------------------
|
|
You can write faster memory access functions if you know whether you are
|
|
fetching from ROM or RAM. Immediate reads are always from the program space
|
|
(Always in ROM unless it is running self-modifying code).
|
|
This will also separate the pc-relative reads, since some systems treat
|
|
PROGRAM mode reads and DATA mode reads differently (for program encryption,
|
|
for instance). See the section below (ADDRESS SPACE) for an explanation of
|
|
PROGRAM and DATA mode.
|
|
|
|
To enable separate reads:
|
|
|
|
- In m68kconf.h, turn on M68K_SEPARATE_READS.
|
|
|
|
- In your host program, implement the following functions:
|
|
unsigned int m68k_read_immediate_16(unsigned int address);
|
|
unsigned int m68k_read_immediate_32(unsigned int address);
|
|
|
|
unsigned int m68k_read_pcrelative_8(unsigned int address);
|
|
unsigned int m68k_read_pcrelative_16(unsigned int address);
|
|
unsigned int m68k_read_pcrelative_32(unsigned int address);
|
|
|
|
- If you need to know the current PC (for banking and such), set
|
|
M68K_MONITOR_PC to OPT_SPECIFY_HANDLER, and set M68K_SET_PC_CALLBACK(A) to
|
|
your routine.
|
|
|
|
|
|
|
|
ADDRESS SPACES:
|
|
--------------
|
|
Most systems will only implement one address space, placing ROM at the lower
|
|
addresses and RAM at the higher. However, there is the possibility that a
|
|
system will implement ROM and RAM in the same address range, but in different
|
|
address spaces, or will have different mamory types that require different
|
|
handling for the program and the data.
|
|
|
|
The 68k accomodates this by allowing different program spaces, the most
|
|
important to us being PROGRAM and DATA space. Here is a breakdown of
|
|
how information is fetched:
|
|
|
|
- All immediate reads are fetched from PROGRAM space.
|
|
|
|
- All PC-relative reads are fetched from PROGRAM space.
|
|
|
|
- The initial stack pointer and program counter are fetched from PROGRAM space.
|
|
|
|
- All other reads (except for those from the moves instruction for 68020)
|
|
are fetched from DATA space.
|
|
|
|
The m68k deals with this by encoding the requested address space on the
|
|
function code pins:
|
|
|
|
FC
|
|
Address Space 210
|
|
------------------ ---
|
|
USER DATA 001
|
|
USER PROGRAM 010
|
|
SUPERVISOR DATA 101
|
|
SUPERVISOR PROGRAM 110
|
|
CPU SPACE 111 <-- not emulated in this core since we emulate
|
|
interrupt acknowledge in another way.
|
|
|
|
Problems arise here if you need to emulate this distinction (if, for example,
|
|
your ROM and RAM are at the same address range, with RAM and ROM enable
|
|
wired to the function code pins).
|
|
|
|
There are 2 ways to deal with this situation using Musashi:
|
|
|
|
1. If you only need the distinction between PROGRAM and DATA (the most common),
|
|
you can just separate the reads (see the preceeding section). This is the
|
|
faster solution.
|
|
|
|
2. You can emulate the function code pins entirely.
|
|
|
|
To emulate the function code pins:
|
|
|
|
- In m68kconf.h, set M68K_EMULATE_FC to OPT_SPECIFY_HANDLER and set
|
|
M68K_SET_FC_CALLBACK(A) to your function code handler function.
|
|
|
|
- Your function code handler should select the proper address space for
|
|
subsequent calls to m68k_read_xx (and m68k_write_xx for 68010+).
|
|
|
|
Note: immediate reads are always done from program space, so technically you
|
|
don't need to implement the separate immediate reads, although you could
|
|
gain more speed improvements leaving them in and doing some clever
|
|
programming.
|
|
|
|
|
|
|
|
USING DIFFERENT CPU TYPES:
|
|
-------------------------
|
|
The default is to enable only the 68000 cpu type. To change this, change the
|
|
settings for M68K_EMULATE_010 etc in m68kconf.h.
|
|
|
|
To set the CPU type you want to use:
|
|
|
|
- Make sure it is enabled in m68kconf.h. Current switches are:
|
|
M68K_EMULATE_010
|
|
M68K_EMULATE_EC020
|
|
M68K_EMULATE_020
|
|
|
|
- In your host program, call m68k_set_cpu_type() and then call
|
|
m68k_pulse_reset(). Valid CPU types are:
|
|
M68K_CPU_TYPE_68000,
|
|
M68K_CPU_TYPE_68010,
|
|
M68K_CPU_TYPE_68EC020,
|
|
M68K_CPU_TYPE_68020
|
|
|
|
|
|
|
|
CLOCK FREQUENCY:
|
|
---------------
|
|
In order to emulate the correct clock frequency, you will have to calculate
|
|
how long it takes the emulation to execute a certain number of "cycles" and
|
|
vary your calls to m68k_execute() accordingly.
|
|
As well, it is a good idea to take away the CPU's timeslice when it writes to
|
|
a memory-mapped port in order to give the device it wrote to a chance to
|
|
react.
|
|
|
|
You can use the functions m68k_cycles_run(), m68k_cycles_remaining(),
|
|
m68k_modify_timeslice(), and m68k_end_timeslice() to do this.
|
|
Try to use large cycle values in your calls to m68k_execute() since it will
|
|
increase throughput. You can always take away the timeslice later.
|
|
|
|
|
|
|
|
MORE CORRECT EMULATION:
|
|
----------------------
|
|
You may need to enable these in order to properly emulate some of the more
|
|
obscure functions of the m68k:
|
|
|
|
- M68K_EMULATE_BKPT_ACK causes the CPU to call a breakpoint handler on a BKPT
|
|
instruction
|
|
|
|
- M68K_EMULATE_TRACE causes the CPU to generate trace exceptions when the
|
|
trace bits are set
|
|
|
|
- M68K_EMULATE_RESET causes the CPU to call a reset handler on a RESET
|
|
instruction.
|
|
|
|
- M68K_EMULATE_PREFETCH emulates the 4-word instruction prefetch that is part
|
|
of the 68000/68010 (needed for Amiga emulation).
|
|
|
|
- call m68k_pulse_halt() to emulate the HALT pin.
|
|
|
|
|
|
|
|
CONVENIENCE FUNCTIONS:
|
|
---------------------
|
|
These are in here for programmer convenience:
|
|
|
|
- M68K_INSTRUCTION_HOOK lets you call a handler before each instruction.
|
|
|
|
- M68K_LOG_ENABLE and M68K_LOG_1010_1111 lets you log illegal and A/F-line
|
|
instructions.
|
|
|
|
|
|
|
|
MULTIPLE CPU EMULATION:
|
|
----------------------
|
|
The default is to use only one CPU. To use more than one CPU in this core,
|
|
there are some things to keep in mind:
|
|
|
|
- To have different cpus call different functions, use OPT_ON instead of
|
|
OPT_SPECIFY_HANDLER, and use the m68k_set_xxx_callback() functions to set
|
|
your callback handlers on a per-cpu basis.
|
|
|
|
- Be sure to call set_cpu_type() for each CPU you use.
|
|
|
|
- Use m68k_set_context() and m68k_get_context() to switch to another CPU.
|
|
|
|
|
|
|
|
LOAD AND SAVE CPU CONTEXTS FROM DISK:
|
|
------------------------------------
|
|
You can use them68k_load_context() and m68k_save_context() functions to load
|
|
and save the CPU state to disk.
|
|
|
|
|
|
|
|
GET/SET INFORMATION FROM THE CPU:
|
|
--------------------------------
|
|
You can use m68k_get_reg() and m68k_set_reg() to gain access to the internals
|
|
of the CPU.
|
|
|
|
|
|
|
|
EXAMPLE:
|
|
-------
|
|
|
|
I have included a file example.zip that contains a full example.
|