[B2-devel] =?us-ascii?Q?B2+SS=3D=3F?=

[Christian B. <cb...@st...>]

Hi!

Because of the stagnant state of BeOS/ppc, the superiority of open sourced
software, and the success of Basilisk II, Marc Hellwig and I (actually just
me because Marc left the decision to me) have decided to make SheepShaver
open source, too.

The internal structure of both programs (B2 and SS) is quite similar (because
B2 was modelled after SS) and in fact, the only difference for many source
files is just the copyright header. With a little more work, I think that
about 80% of the source files could be shared between both projects.

The logical conclusion is thus to merge both projects in some way. The most
extreme (but probably possible) way would be to put both 68k and PPC Mac
emulation into one program. Which CPU architecture will be emulated is then
decided by the type of ROM being used. A couple of thoughts about this:

 1. The most important issue to be resolved is of course: how should this
    combined emulator be named? :-)
    "Basilisk III" sounds a bit boring and is also not completely accurate
    since Basilisk II was named this way because it (originally) emulated
    a Mac II class machine, not so much because it was the successor to the
    original "Basilisk". I also like the "SheepShaver" name.
 2. SheepShaver only has native PowerPC support. There is no PowerPC emulation
    for other systems yet (I've started with a simple interpreter but this
    would need a lot more work to be usable, let alone efficient enough).
 3. Some things need a little rearranging. We would now be concerned with
    3 different configurations:
     - native 68k, emulated PPC (possible, but probably too slow to make
       much sense)
     - emulated 68k (could use 68k emulation from MacOS ROM), native PPC
     - emulated 68k, emulated PPC
 4. Because there is only one set of MacOS memory access functions, it is
    necessary for the emulator to run in the same addressing mode, whether
    a 68k or a PPC Mac is to be emulated. Luckily, 68k and PPC have the same
    endianess and alignment restrictions. So on a native 68k machine, the
    PPC emulation will have to run in real addressing mode, which is possible
    (likewise for a native PPC machine).
 5. The memory access subsystem will have to be separated from the CPU
    emulation (currently the memory access is from UAE's 68k emulator) to
    make it possible for 68k and PPC emulation to use the same memory module.
 6. Due to the way SheepShaver works, it needs 12k of Low Memory globals
    (instead of 8k as B2, or 10k as a real PowerMac). But this shouldn't be
    a problem.
 7. Because SheepShaver was designed for PPC systems, there are many places
    where it more or less directly jumps into MacOS code. These places will
    have to be rewritten carefully.
 8. This especially affects the SheepShaver Ethernet driver which is
    completely different from the B2 one. It is a proper DLPI module for
    Open Transport and as such calls many OT functions for message and
    queue management, and it also requires OT headers which cannot be
    included in a source release.
 9. Video mode selection is also different because SheepShaver provides
    run-time mode and depth switching (there is a nice and clean interface
    for PCI video drivers for doing this). But with some clever redesign,
    this should provide the 68k emulation with mode/depth switching, too.

In any case, I would like to have at least one more stable release of
Basilisk II (with JIT) before starting with this (probably not this year
any more).

Bye,
Christian

-- 
  / Coding on PowerPC and proud of it
\/ http://www.uni-mainz.de/~bauec002/