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BASILISK II TECHNICAL MANUAL |
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============================ |
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|
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0. Table of Contents |
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-------------------- |
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|
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1. Introduction |
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2. Modes of operation |
| 9 |
3. Memory access |
| 10 |
4. Calling native routines from 68k mode and vice-versa |
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5. Interrupts |
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6. Parts of Basilisk II |
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7. Porting Basilisk II |
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|
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1. Introduction |
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--------------- |
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|
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Basilisk II can emulate two kind of Macs, depending on the ROM being used: |
| 19 |
|
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1. A Mac Classic |
| 21 |
2. A Mac II series computer ("Mac II series" here means all 68020/30/40 |
| 22 |
based Macs with 32-bit clean ROMs (this excludes the original Mac II, |
| 23 |
the IIx/IIcx and the SE/030), except PowerBooks; in the following, |
| 24 |
"Mac II" is used as an abbreviation of "Mac II series computer", as |
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defined above) |
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|
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More precisely spoken, MacOS under Basilisk II behaves like on a Mac Classic |
| 28 |
or Mac II because, apart from the CPU, the RAM and the ROM, absolutely no Mac |
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hardware is emulated. Rather, Basilisk II provides replacements (usually in |
| 30 |
the form of MacOS drivers) for the parts of MacOS that access hardware. As |
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there are practically no Mac applications that access hardware directly (this |
| 32 |
is also due to the fact that the hardware of different Mac models is sometimes |
| 33 |
as different as, say, the hardware of an Atari ST and an Amiga 500), both the |
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compatibility and speed of this approach are very high. |
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|
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2. Modes of operation |
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--------------------- |
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|
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Basilisk II is designed to run on many different hardware platforms and on |
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many different operating systems. To provide optimal performance under all |
| 41 |
environments, it can run in three different modes, depending on the features |
| 42 |
of the underlying environment (the modes are selected with the REAL_ADDRESSING |
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and EMULATED_68K defines in "sysdeps.h"): |
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|
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1. Emulated CPU, "virtual" addressing (EMULATED_68K = 1, REAL_ADDRESSING = 0): |
| 46 |
This mode is designed for non-68k or little-endian systems or systems that |
| 47 |
don't allow accessing RAM at 0x0000..0x1fff. This is also the only mode that |
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allows 24-bit addressing, and thus the only mode that allows Mac Classic |
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emulation. The 68k processor is emulated with the UAE CPU engine and two |
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memory areas are allocated for Mac RAM and ROM. The memory map seen by the |
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emulated CPU and the host CPU are different. Mac RAM starts at address 0 |
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for the emulated 68k, but it may start at a different address for the host |
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CPU. All memory accesses of the CPU emulation go through memory access |
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functions (do_get_mem_long() etc.) that translate addresses. This slows |
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down the emulator, of course. |
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|
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2. Emulated CPU, "real" addressing (EMULATED_68K = 1, REAL_ADDRESSING = 0): |
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This mode is intended for big-endian non-68k systems that do allow access to |
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RAM at 0x0000..0x1fff. As in the virtual addressing mode, the 68k processor |
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is emulated with the UAE CPU engine and two areas are set up for RAM and ROM |
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but the emulated CPU lives in the same address space as the host CPU. |
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This means that if something is located at a certain address for the 68k, |
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it is located at the exact same address for the host CPU. Mac addresses |
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and host addresses are the same. The memory accesses of the CPU emulation |
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still go through access functions but the address translation is no longer |
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needed, and if the host CPU uses big-endian data layout and can handle |
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unaligned accesses like the 68k, the memory access functions are replaced |
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by direct, inlined memory accesses, making for the fastest possible speed |
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of the emulator. |
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A usual consequence of the real addressing mode is that the Mac RAM doesn't |
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any longer begin at address 0 for the Mac and that the Mac ROM also is not |
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located where it usually is on a real Mac. But as the Mac ROM is relocatable |
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and the available RAM is defined for MacOS by the start of the system zone |
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(which is relocated to the start of the allocated RAM area) and the MemTop |
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variable (which is also set correctly) this is not a problem. There is, |
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however, one RAM area that must lie in a certain address range. This area |
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contains the Mac "Low Memory Globals" which (on a Mac II) are located at |
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0x0000..0x1fff and which cannot be moved to a different address range. |
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The Low Memory Globals constitute of many important MacOS and application |
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global variables (e.g. the above mentioned "MemTop" variable which is |
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located at 0x0108). For the real addressing mode to work, the host CPU |
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needs access to 0x0000..0x1fff. Under most operating systems, this is a |
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big problem. On some systems, patches (like PrepareEmul on the Amiga or |
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the sheep_driver under BeOS) can be installed to "open up" this area. On |
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other systems, it might be possible to use access exception handlers to |
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emulate accesses to this area. But if the Low Memory Globals area cannot |
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be made available, using the real addressing mode is not possible. |
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|
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3. Native CPU (EMULATED_68K = 0, this also requires REAL_ADDRESSING = 1) |
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This mode is designed for systems that use a 68k (68020 or better) processor |
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as host CPU and is the technically most difficult mode to handle. The Mac |
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CPU is no longer emulated (the UAE CPU emulation is not needed) but MacOS |
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and Mac applications run natively on the existing 68k CPU. This means that |
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the emulator has its maximum possible speed (very close to that of a real |
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Mac with the same CPU). As there is no control over the memory accesses of |
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the CPU, real addressing mode is implied, and so the Low Memory area must |
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be accessible (an MMU might be used to set up different address spaces for |
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the Mac and the host, but this is not implemented in Basilisk II). The |
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native CPU mode has some possible pitfalls that might make its |
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implementation difficult on some systems: |
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a) Implied real addressing (this also means that Mac programs that go out |
| 102 |
of control can crash the emulator or the whole system) |
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b) MacOS and Mac applications assume that they always run in supervisor |
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mode (more precisely, they assume that they can safely use certain |
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priviledged instructions, mostly for interrupt control). So either |
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the whole emulator has to be run in supervisor mode (which usually is |
| 107 |
not possible on multitasking systems) or priviledged instructions have |
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to be trapped and emulated. The Amiga version of Basilisk II uses the |
| 109 |
latter approach (it is possible to run supervisor mode tasks under |
| 110 |
the AmigaOS multitasking kernel (ShapeShifter does this) but it |
| 111 |
requires modifying the task switcher and makes the emulator more |
| 112 |
unstable). |
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c) On multitasking systems, interrupts can usually not be handled as on |
| 114 |
a real Mac (or with the UAE CPU). The interrupt levels of the host |
| 115 |
will not be the same as on a Mac, and the operating systems might not |
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allow installing hardware interrupt handlers or the interrupt handlers |
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might have different stack frames and run-time environments than 68k |
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hardware interrupts. The usual solution is to use some sort of software |
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interrupts or signals to interrupt the main emulation process and to |
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manually call the Mac 68k interrupt handler with a faked stack frame. |
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d) 68060 systems are a small problem because there is no Mac that ever |
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used the 68060 and MacOS doesn't know about this processor. Basilisk II |
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reports the 68060 as being a 68040 to the MacOS and patches some places |
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where MacOS makes use of certain 68040-specific features such as the |
| 125 |
FPU state frame layout or the PTEST instruction. Also, Basilisk II |
| 126 |
requires that all of the Motorola support software for the 68060 to |
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emulate missing FPU and integer instructions and addressing modes is |
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provided by the host operating system (this also applies to the 68040). |
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e) The "EMUL_OP" mechanism described below requires the interception and |
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handling of certain emulator-defined instructions. |
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|
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3. Memory access |
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---------------- |
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|
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There is often a need to access Mac RAM and ROM inside the emulator. As |
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Basilisk II may run in "real" or "virtual" addressing mode on many different |
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architectures, big-endian or little-endian, certain platform-independent |
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data types and functions are provided: |
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|
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a) "sysdeps.h" defines the types int8, uint8, int16, uint16, int32 and uint32 |
| 141 |
for numeric quantities of a certain signedness and bit length |
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b) "cpu_emulation.h" defines the ReadMacInt*() and WriteMacInt*() functions |
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which should always be used to read from or write to Mac RAM or ROM |
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c) "cpu_emulation.h" also defines the Mac2HostAddr() function that translates |
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a Mac memory address to a (uint8 *) in host address space. This allows you |
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to access larger chunks of Mac memory directly, without going through the |
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read/write functions for every access. But doing so you have to perform |
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any needed endianess conversion of the data yourself by using the ntohs() |
| 149 |
etc. macros which are available on most systems or defined in "sysdeps.h". |
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|
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4. Calling native routines from 68k mode and vice-versa |
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------------------------------------------------------- |
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|
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An emulator like Basilisk II requires two kinds of cross-platform function |
| 155 |
calls: |
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|
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a) Calling a native routine from the Mac 68k context |
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b) Calling a Mac 68k routine from the native context |
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|
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Situation a) arises in nearly all Basilisk drivers and system patches while |
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case b) is needed for the invocation of Mac call-back or interrupt routines. |
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Basilisk II tries to solve both problems in a way that provides the same |
| 163 |
interface whether it is running on a 68k or a non-68k system. |
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|
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4.1. The EMUL_OP mechanism |
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-------------------------- |
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|
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Calling native routines from the Mac 68k context requires breaking out of the |
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68k emulator or interrupting the current instruction flow and is done via |
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unimplemented 68k opcodes (called "EMUL_OP" opcodes). Basilisk II uses opcodes |
| 171 |
of the form 0x71xx (these are invalid MOVEQ opcodes) which are defined in |
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"emul_op.h". When such an opcode is encountered, whether by the emulated CPU |
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or a real 68k, the execution is interrupted, all CPU registers saved and the |
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EmulOp() function from "emul_op.cpp" is called. EmulOp() decides which opcode |
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caused the interrupt and performs the required actions (mostly by calling other |
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emulator routines). The EMUL_OP handler routines have access to nearly all of |
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the 68k user mode registers (exceptions being the PC, A7 and SR). So the |
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EMUL_OP opcodes can be thought of as extensions to the 68k instruction set. |
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Some of these opcodes are used to implement ROM or resource patches because |
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they only occupy 2 bytes and there is sometimes not more room for a patch. |
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|
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4.2. Execute68k() |
| 183 |
----------------- |
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|
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"cpu_emulation.h" declares the functions Execute68k() and Execute68kTrap() to |
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call Mac 68k routines or MacOS system traps from inside an EMUL_OP handler |
| 187 |
routine. They allow setting all 68k user mode registers (except PC and SR) |
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before the call and examining all register contents after the call has |
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returned. EMUL_OP and Execute68k() may be nested, i.e. a routine called with |
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Execute68k() may contain EMUL_OP opcodes and the EMUL_OP handlers may in turn |
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call Execute68k() again. |
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|
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5. Interrupts |
| 194 |
------------- |
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|
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Various parts of Basilisk II (such as the Time Manager and the serial driver) |
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need an interrupt facility to trigger asynchronous events. The MacOS uses |
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different 68k interrupt levels for different events, but for simplicity |
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Basilisk II only uses level 1 and does it's own interrupt dispatching. The |
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"InterruptFlags" contains a bit mask of the pending interrupts. These are the |
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currently defined interrupt sources (see main.h): |
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|
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INTFLAG_60HZ - MacOS 60Hz interrupt (unlike a real Mac, we also handle |
| 204 |
VBL interrupts, ADB events and the Time Manager here) |
| 205 |
INTFLAG_SERIAL - Interrupt for serial driver I/O completion |
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INTFLAG_ETHER - Interrupt for Ethernet driver I/O completion and packet |
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reception |
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INTFLAG_AUDIO - Interrupt for audio "next block" requests |
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INTFLAG_TIMER - Reserved for a future implementation of a more precise |
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Time Manager (currently not used) |
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|
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An interrupt is triggered by calling SetInterruptFlag() with the desired |
| 213 |
interrupt flag constant and then TriggerInterrupt(). When the UAE 68k |
| 214 |
emulator is used, this will signal a hardware interrupt to the emulated 680x0. |
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On a native 68k machine, some other method for interrupting the MacOS thread |
| 216 |
has to be used (e.g. on AmigaOS, a signal exception is used). Care has to be |
| 217 |
taken because with the UAE CPU, the interrupt will only occur when Basilisk II |
| 218 |
is executing MacOS code while on a native 68k machine, the interrupt could |
| 219 |
occur at any time (e.g. inside an EMUL_OP handler routine). In any case, the |
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MacOS thread will eventually end up in the level 1 interrupt handler which |
| 221 |
contains an M68K_EMUL_OP_IRQ opcode. The opcode handler in emul_op.cpp will |
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then look at InterruptFlags and decide which routines to call. |
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|
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6. Parts of Basilisk II |
| 225 |
----------------------- |
| 226 |
|
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The conception of Basilisk II is quite modular and consists of many parts |
| 228 |
which are relatively independent from each other: |
| 229 |
|
| 230 |
- UAE CPU engine ("uae_cpu/*", not needed on all systems) |
| 231 |
- ROM patches ("rom_patches.cpp", "slot_rom.cpp" and "emul_op.cpp") |
| 232 |
- resource patches ("rsrc_patches.cpp" and "emul_op.cpp") |
| 233 |
- PRAM Utilities replacement ("xpram.cpp") |
| 234 |
- ADB Manager replacement ("adb.cpp") |
| 235 |
- Time Manager replacement ("timer.cpp") |
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- SCSI Manager replacement ("scsi.cpp") |
| 237 |
- video driver ("video.cpp") |
| 238 |
- audio component ("audio.cpp") |
| 239 |
- floppy driver ("sony.cpp") |
| 240 |
- disk driver ("disk.cpp") |
| 241 |
- CD-ROM driver ("cdrom.cpp") |
| 242 |
- external file system ("extfs.cpp") |
| 243 |
- serial drivers ("serial.cpp") |
| 244 |
- Ethernet driver ("ether.cpp") |
| 245 |
- system-dependant device access ("sys_*.cpp") |
| 246 |
- user interface strings ("user_strings.cpp") |
| 247 |
- preferences management ("prefs.cpp" and "prefs_editor_*.cpp") |
| 248 |
|
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Most modules consist of a platform-independant part (such as video.cpp) and a |
| 250 |
platform-dependant part (such as video_beos.cpp). The "dummy" directory |
| 251 |
contains generic "do-nothing" versions of some of the platform-dependant |
| 252 |
parts to aid in testing and porting. |
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|
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6.1. UAE CPU engine |
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------------------- |
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|
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All files relating to the UAE 680x0 emulation are kept in the "uae_cpu" |
| 258 |
directory. The "cpu_emulation.h" header file defines the link between the |
| 259 |
UAE CPU and the rest of Basilisk II, and "basilisk_glue.cpp" implements the |
| 260 |
link. It should be possible to replace the UAE CPU with a different 680x0 |
| 261 |
emulation by creating a new "xxx_cpu" directory with an appropriate |
| 262 |
"cpu_emulation.h" header file (for the inlined memory access functions) and |
| 263 |
writing glue code between the functions declared in "cpu_emulation.h" and |
| 264 |
those provided by the 680x0 emulator. |
| 265 |
|
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6.2. ROM and resource patches |
| 267 |
----------------------------- |
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|
| 269 |
As described above, instead of emulating custom Mac hardware, Basilisk II |
| 270 |
provides replacements for certain parts of MacOS to redirect input, output |
| 271 |
and system control functions of the Mac hardware to the underlying operating |
| 272 |
systems. This is done by applying patches to the Mac ROM ("ROM patches") and |
| 273 |
the MacOS system file ("resource patches", because nearly all system software |
| 274 |
is contained in MacOS resources). Unless resources are written back to disk, |
| 275 |
the system file patches are not permanent (it would cause many problems if |
| 276 |
they were permanent, because some of the patches vary with different |
| 277 |
versions of Basilisk II or even every time the emulator is launched). |
| 278 |
|
| 279 |
ROM patches are contained in "rom_patches.cpp" and resource patches are |
| 280 |
contained in "rsrc_patches.cpp". The ROM patches are far more numerous because |
| 281 |
nearly all the software needed to run MacOS is contained in the Mac ROM (the |
| 282 |
system file itself consists mainly of ROM patches, in addition to pictures and |
| 283 |
text). One part of the ROM patches involves the construction of a NuBus slot |
| 284 |
declaration ROM (in "slot_rom.cpp") which is used to add the video and Ethernet |
| 285 |
drivers. Apart from the CPU emulation, the ROM and resource patches contain |
| 286 |
most of the "logic" of the emulator. |
| 287 |
|
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6.3. PRAM Utilities |
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------------------- |
| 290 |
|
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MacOS stores certain nonvolatile system parameters in a 256 byte battery |
| 292 |
backed-up CMOS RAM area called "Parameter RAM", "PRAM" or "XPRAM" (which refers |
| 293 |
to "Extended PRAM" because the earliest Mac models only had 20 bytes of PRAM). |
| 294 |
Basilisk II patches the ClkNoMem() MacOS trap which is used to access the XPRAM |
| 295 |
(apart from some routines which are only used early during system startup) |
| 296 |
and the real-time clock. The XPRAM is emulated in a 256 byte array which is |
| 297 |
saved to disk to preserve the contents for the next time Basilisk is launched. |
| 298 |
|
| 299 |
6.4. ADB Manager |
| 300 |
---------------- |
| 301 |
|
| 302 |
For emulating a mouse and a keyboard, Basilisk II patches the ADBOp() MacOS |
| 303 |
trap. Platform-dependant code reports mouse and keyboard events with the |
| 304 |
ADBMouseDown() etc. functions which are queued and sent to MacOS inside the |
| 305 |
ADBInterrupt() function (which is called as a part of the 60Hz interrupt |
| 306 |
handler) by calling the ADB mouse and keyboard handlers with Execute68k(). |
| 307 |
|
| 308 |
6.5. Time Manager |
| 309 |
----------------- |
| 310 |
|
| 311 |
Basilisk II completely replaces the Time Manager (InsTime(), RmvTime(), |
| 312 |
PrimeTime() and Microseconds() traps). A "TMDesc" structure is associated with |
| 313 |
each Time Manager task, that contains additional data. The tasks are executed |
| 314 |
in the TimerInterrupt() function which is currently called inside the 60Hz |
| 315 |
interrupt handler, thus limiting the resolution of the Time Manager to 16.6ms. |
| 316 |
|
| 317 |
6.6. SCSI Manager |
| 318 |
----------------- |
| 319 |
|
| 320 |
The (old-style) SCSI Manager is also completely replaced and the MacOS |
| 321 |
SCSIDispatch() trap redirected to the routines in "scsi.cpp". Under the MacOS, |
| 322 |
programs have to issue multiple calls for all the different phases of a |
| 323 |
SCSI bus interaction (arbitration, selection, command transfer etc.). |
| 324 |
Basilisk II maps this API to an atomic API which is used by most modern |
| 325 |
operating systems. All action is deferred until the call to SCSIComplete(). |
| 326 |
The TIB (Transfer Instruction Block) mini-programs used by the MacOS are |
| 327 |
translated into a scatter/gather list of data blocks. Operating systems that |
| 328 |
don't support scatter/gather SCSI I/O will have to use buffering if more than |
| 329 |
one data block is being transmitted. Some more advanced (but rarely used) |
| 330 |
aspects of the SCSI Manager (like messaging and compare operations) are not |
| 331 |
emulated. |
| 332 |
|
| 333 |
6.7. Video driver |
| 334 |
----------------- |
| 335 |
|
| 336 |
The NuBus slot declaration ROM constructed in "slot_rom.cpp" contains a driver |
| 337 |
definition for a video driver. The Control and Status calls of this driver are |
| 338 |
implemented in "video.cpp". Run-time video mode and depth switching are |
| 339 |
currently not supported. |
| 340 |
|
| 341 |
The host-side initialization of the video system is done in VideoInit(). |
| 342 |
This function must provide access to a frame buffer for MacOS and supply |
| 343 |
its address, resolution and color depth in a video_desc structure (there |
| 344 |
is currently only one video_desc structure, called VideoMonitor; this is |
| 345 |
going to change once multiple displays are supported). In real addressing |
| 346 |
mode, this frame buffer must be in a MacOS compatible layout (big-endian |
| 347 |
and 1, 2, 4 or 8 bits paletted chunky pixels, RGB 5:5:5 or xRGB 8:8:8:8). |
| 348 |
In virtual addressing mode, the frame buffer is located at address |
| 349 |
0xa0000000 on the Mac side and you have to supply the host address, size |
| 350 |
and layout (BasiliskII will do an automatic pixel format conversion in |
| 351 |
virtual addressing mode) in the variables MacFrameBaseHost, MacFrameSize |
| 352 |
and MacFrameLayout. |
| 353 |
|
| 354 |
6.8. Audio component |
| 355 |
-------------------- |
| 356 |
|
| 357 |
Basilisk II provides a Sound Manager 3.x audio component for sound output. |
| 358 |
Earlier Sound Manager versions that don't use components but 'snth' resources |
| 359 |
are not supported. Nearly all component functions are implemented in |
| 360 |
"audio.cpp". The system-dependant modules ("audio_*.cpp") handle the |
| 361 |
initialization of the audio hardware/driver, volume controls, and the actual |
| 362 |
sound output. |
| 363 |
|
| 364 |
The mechanism of sound output varies depending on the platform but usually |
| 365 |
there will be one "streaming thread" (either a thread that continuously writes |
| 366 |
data buffers to the audio device or a callback function that provides the |
| 367 |
next data buffer) that reads blocks of sound data from the MacOS Sound Manager |
| 368 |
and writes them to the audio device. To request the next data buffer, the |
| 369 |
streaming thread triggers the INTFLAG_AUDIO interrupt which will cause the |
| 370 |
MacOS thread to eventually call AudioInterrupt(). Inside AudioInterrupt(), |
| 371 |
the next data block will be read and the streaming thread is signalled that |
| 372 |
new audio data is available. |
| 373 |
|
| 374 |
6.9. Floppy, disk and CD-ROM drivers |
| 375 |
------------------------------------ |
| 376 |
|
| 377 |
Basilisk II contains three MacOS drivers that implement floppy, disk and CD-ROM |
| 378 |
access ("sony.cpp", "disk.cpp" and "cdrom.cpp"). They rely heavily on the |
| 379 |
functionality provided by the "sys_*.cpp" module. BTW, the name ".Sony" of the |
| 380 |
MacOS floppy driver comes from the fact that the 3.5" floppy drive in the first |
| 381 |
Mac models was custom-built for Apple by Sony (this was one of the first |
| 382 |
applications of the 3.5" floppy format which was also invented by Sony). |
| 383 |
|
| 384 |
6.10. External file system |
| 385 |
-------------------------- |
| 386 |
|
| 387 |
Basilisk II also provides a method for accessing files and direcories on the |
| 388 |
host OS from the MacOS side by means of an "external" file system (henceforth |
| 389 |
called "ExtFS"). The ExtFS is built upon the File System Manager 1.2 interface |
| 390 |
that is built into MacOS 7.6 (and later) and available as a system extension |
| 391 |
for earlier MacOS versions. Unlike other parts of Basilisk II, extfs.cpp |
| 392 |
requires POSIX file I/O and this is not going to change any time soon, so if |
| 393 |
you are porting Basilisk II to a system without POSIX file functions, you |
| 394 |
should emulate them. |
| 395 |
|
| 396 |
6.11. Serial drivers |
| 397 |
-------------------- |
| 398 |
|
| 399 |
Similar to the disk drivers, Basilisk II contains replacement serial drivers |
| 400 |
for the emulation of Mac modem and printer ports. To avoid duplicating code, |
| 401 |
both ports are handled by the same set of routines. The SerialPrime() etc. |
| 402 |
functions are mostly wrappers that determine which port is being accessed. |
| 403 |
All the real work is done by the "SERDPort" class which is subclassed by the |
| 404 |
platform-dependant code. There are two instances (for port A and B) of the |
| 405 |
subclasses. |
| 406 |
|
| 407 |
Unlike the disk drivers, the serial driver must be able to handle asynchronous |
| 408 |
operations. Calls to SerialPrime() will usually not actually transmit or receive |
| 409 |
data but delegate the action to an independant thread. SerialPrime() then |
| 410 |
returns "1" to indicate that the I/O operation is not yet completed. The |
| 411 |
completion of the I/O request is signalled by calling the MacOS trap "IODone". |
| 412 |
However, this can't be done by the I/O thread because it's not in the right |
| 413 |
run-time environment to call MacOS functions. Therefore it will trigger the |
| 414 |
INTFLAG_SERIAL interrupt which causes the MacOS thread to eventually call |
| 415 |
SerialInterrupt(). SerialInterrupt(), in turn, will not call IODone either but |
| 416 |
install a Deferred Task to do the job. The Deferred Task will be called by |
| 417 |
MacOS when it returns to interrupt level 0. This mechanism sounds complicated |
| 418 |
but is necessary to ensure stable operation of the serial driver. |
| 419 |
|
| 420 |
6.12. Ethernet driver |
| 421 |
--------------------- |
| 422 |
|
| 423 |
A driver for Ethernet networking is also contained in the NuBus slot ROM. |
| 424 |
Only one ethernet card can be handled by Basilisk II. For Ethernet to work, |
| 425 |
Basilisk II must be able to send and receive raw Ethernet packets, including |
| 426 |
the 14-byte header (destination and source address and type/length field), |
| 427 |
but not including the 4-byte CRC. This may not be possible on all platforms |
| 428 |
or it may require writing special net drivers or add-ons or running with |
| 429 |
superuser priviledges to get access to the raw packets. |
| 430 |
|
| 431 |
Writing packets works as in the serial drivers. The ether_write() routine may |
| 432 |
choose to send the packet immediately (e.g. under BeOS) and return noErr or to |
| 433 |
delegate the sending to a separate thread (e.g. under AmigaOS) and return "1" to |
| 434 |
indicate that the operation is still in progress. For the latter case, a |
| 435 |
Deferred Task structure is provided in the ether_data area to call IODone from |
| 436 |
EtherInterrupt() when the packet write is complete (see above for a description |
| 437 |
of the mechanism). |
| 438 |
|
| 439 |
Packet reception is a different story. First of all, there are two methods |
| 440 |
provided by the MacOS Ethernet driver API to read packets, one of which (ERead/ |
| 441 |
ERdCancel) is not supported by Basilisk II. Basilisk II only supports reading |
| 442 |
packets by attaching protocol handlers. This shouldn't be a problem because |
| 443 |
the only network code I've seen so far that uses ERead is some Apple sample |
| 444 |
code. AppleTalk, MacTCP, MacIPX, OpenTransport etc. all use protocol handlers. |
| 445 |
By attaching a protocol handler, the user of the Ethernet driver supplies a |
| 446 |
handler routine that should be called by the driver upon reception of Ethernet |
| 447 |
packets of a certain type. 802.2 packets (type/length field of 0..1500 in the |
| 448 |
packet header) are a bit special: there can be only one protocol handler attached |
| 449 |
for 802.2 packets (by specifying a packet type of "0"). The MacOS LAP Manager |
| 450 |
will attach a 802.2 handler upon startup and handle the distribution of 802.2 |
| 451 |
packets to sub-protocol handlers, but the Basilisk II Ethernet driver is not |
| 452 |
concerned with this. |
| 453 |
|
| 454 |
When the driver receives a packet, it has to look up the protocol handler |
| 455 |
installed for the respective packet type (if any has been installed at all) |
| 456 |
and call the packet handler routine. This must be done with Execute68k() from |
| 457 |
the MacOS thread, so an interrupt (INTFLAG_ETHER) is triggered upon reception |
| 458 |
of a packet so the EtherInterrupt() routine can call the protocol handler. |
| 459 |
Before calling the handler, the Ethernet packet header has to be copied to |
| 460 |
MacOS RAM (the "ed_RHA" field of the ether_data structure is provided for this). |
| 461 |
The protocol handler will read the packet data by means of the ReadPacket/ReadRest |
| 462 |
routines supplied by the Ethernet driver. Both routines will eventually end up |
| 463 |
in EtherReadPacket() which copies the data to Mac address space. EtherReadPacket() |
| 464 |
requires the host address and length of the packet to be loaded to a0 and d1 |
| 465 |
before calling the protocol handler. |
| 466 |
|
| 467 |
Does this sound complicated? You are probably right. Here is another description |
| 468 |
of what happens upon reception of a packet: |
| 469 |
1. Ethernet card receives packet and notifies some platform-dependant entity |
| 470 |
inside Basilisk II |
| 471 |
2. This entity will store the packet in some safe place and trigger the |
| 472 |
INTFLAG_ETHER interrupt |
| 473 |
3. The MacOS thread will execute the EtherInterrupt() routine and look for |
| 474 |
received packets |
| 475 |
4. If a packet was received of a type to which a protocol handler had been |
| 476 |
attached, the packet header is copied to ed_RHA, a0/d1 are loaded with |
| 477 |
the host address and length of the packet data, a3 is loaded with the |
| 478 |
Mac address of the first byte behing ed_RHA and a4 is loaded with the |
| 479 |
Mac address of the ed_ReadPacket code inside ether_data, and the protocol |
| 480 |
handler is called with Execute68k() |
| 481 |
5. The protocol handler will eventually try to read the packet data with |
| 482 |
a "jsr (a4)" or "jsr 2(a4)" |
| 483 |
6. This will execute an M68K_EMUL_OP_ETHER_READ_PACKET opcode |
| 484 |
7. The EtherReadPacket() opcode handling routine will copy the requested |
| 485 |
part of the packet data to Mac RAM using the pointer and length which are |
| 486 |
still in a0/d1 |
| 487 |
|
| 488 |
For a more detailed description of the Ethernet driver, see "Inside AppleTalk". |
| 489 |
|
| 490 |
6.13. System-dependant device access |
| 491 |
------------------------------------ |
| 492 |
|
| 493 |
The method for accessing floppy drives, hard disks, CD-ROM drives and files |
| 494 |
vary greatly between different operating systems. To make Basilisk II easily |
| 495 |
portable, all device I/O is made via the functions declared in "sys.h" and |
| 496 |
implemented by the (system-dependant) "sys_*.cpp" modules which provides a |
| 497 |
standard, Unix-like interface to all kinds of devices. |
| 498 |
|
| 499 |
6.14. User interface strings |
| 500 |
---------------------------- |
| 501 |
|
| 502 |
To aid in localization, all user interface strings of Basilisk II are collected |
| 503 |
in "user_strings.cpp" (for common strings) and "user_strings_*.cpp" (for |
| 504 |
platform-specific strings), and accessed via the GetString() function. This |
| 505 |
way, Basilisk II may be easily translated to different languages. |
| 506 |
|
| 507 |
6.15. Preferences management |
| 508 |
---------------------------- |
| 509 |
|
| 510 |
The module "prefs.cpp" handles user preferences in a system-independant way. |
| 511 |
Preferences items are accessed with the PrefsAdd*(), PrefsReplace*() and |
| 512 |
PrefsFind*() functions and stored in human-readable and editable text files |
| 513 |
on disk. There are two lists of available preferences items. The first one, |
| 514 |
common_prefs_items, defines the items which are available on all systems. |
| 515 |
The second one, platform_prefs_items, is defined in prefs_*.cpp and lists |
| 516 |
the prefs items which are specific to a certain platform. |
| 517 |
|
| 518 |
The "prefs_editor_*.cpp" module provides a graphical user interface for |
| 519 |
setting the preferences so users won't have to edit the preferences file |
| 520 |
manually. |
| 521 |
|
| 522 |
7. Porting Basilisk II |
| 523 |
---------------------- |
| 524 |
|
| 525 |
Porting Basilisk II to a new platform should not be hard. These are the steps |
| 526 |
involved in the process: |
| 527 |
|
| 528 |
1. Create a new directory inside the "src" directory for your platform. If |
| 529 |
your platform comes in several "flavours" that require adapted files, you |
| 530 |
should consider creating subdirectories inside the platform directory. |
| 531 |
All files needed for your port must be placed inside the new directory. |
| 532 |
Don't scatter platform-dependant files across the "src" hierarchy. |
| 533 |
2. Decide in which mode (virtual addressing, real addressing or native CPU) |
| 534 |
Basilisk II will run. |
| 535 |
3. Create a "sysdeps.h" file which defines the mode and system-dependant |
| 536 |
data types and memory access functions. Things which are used in Basilisk |
| 537 |
but missing on your platform (such as endianess macros) should also be |
| 538 |
defined here. |
| 539 |
4. Implement the system-specific parts of Basilisk: |
| 540 |
main_*.cpp, sys_*.cpp, prefs_*.cpp, prefs_editor_*.cpp, xpram_*.cpp, |
| 541 |
timer_*.cpp, audio_*.cpp, video_*.cpp, serial_*.cpp, ether_*.cpp, |
| 542 |
scsi_*.cpp and clip_*.cpp |
| 543 |
You may want to take the skeleton implementations in the "dummy" directory |
| 544 |
as a starting point and look at the implementation for other platforms |
| 545 |
before writing your own. |
| 546 |
5. Important things to remember: |
| 547 |
- Use the ReadMacInt*() and WriteMacInt*() functions from "cpu_emulation.h" |
| 548 |
to access Mac memory |
| 549 |
- Use the ntohs() etc. macros to convert endianess when accessing Mac |
| 550 |
memory directly |
| 551 |
- Don't modify any source files outside of your platform directory unless |
| 552 |
you really, really have to. Instead of adding "#ifdef PLATFORM" blocks |
| 553 |
to one of the platform-independant source files, you should contact me |
| 554 |
so that we may find a more elegant and more portable solution. |
| 555 |
6. Coding style: indent -kr -ts4 |
| 556 |
|
| 557 |
|
| 558 |
Christian Bauer |
| 559 |
<Christian.Bauer@uni-mainz.de> |
