oTOSis - V0.22
		 By Elias Martenson, elias@omicron.se
				   

This is a new version of the TOS emulator for Linux/68K.

The name has been changed. Or rather, it didn't have a name before and
now it's got the name oTOSis.

Some MiNT support is implemented. It's enabled using the -m flag.

Hardware register support has been started on.


		     WHAT WORKS IN THIS VERSION?

Some programs run, most notably Pure C.

The compiler (pcc.ttp) runs. plink.ttp used to run but don't anmore.
See the problem decription later in this document.


		     HOW DOES THIS EMULATOR WORK?

Since I know very little about how emulation of other operating
systems should be made on the kernel level, I decided to attempt to
make a TOS-emulator that requires no kernel hacking, and that can be
run as a user process. The result is what you see here.

When a user process attempts to perform an illegal trap, that is, any
trap except for trap #0, it generates a SIGILL. The emulator traps
SIGILL, and the signal handler looks in the stack frame to see what
instruction caused the signal. If the instruction is "trap" then the
vector number is checked and the appropriate function is called. Then,
after the call has been performed, the return value is written onto
the stack so that the signal handler restores this number into d0
instead of the old value that was saved before the call to the signal
handler. These hacks with the stack is propably quite unportable, and
I suppose that the offsets used might not work in newer versions of
the kernel.

The loader loads a TOS-program, relocates it, and sets up a basepage.
It then sets up the signal handler and jumps to the TOS-programs start
address.


			   CURRENT PROBLEMS

When running teh emulator as ELF, malloc()'ed memory is in the
upper half of the address space. This causes some TOS programs
to think that Malloc returned an error, and thinks that there
is not enough memory left. The Pure C linker is a good example
for this.


			   WHAT IS PLANNED?

Then some kind of configuration options would be nice, a lot of values
are hard coded right now, and all TOS drives are actually pointing to
the root directory on the Linux filesystem. It would be nice to be
able to map a specific TOS-drive on a directory.

The plan is to integrate oTOSis with the AES called oAESis that has
already been written and runs under MiNT. For this we need oVDIsis
that Stefan Berndtsson (gubsb@trivux.ub.gu.se) is working on. When
this is finished it should be possible to run GEM programs under
Linux. The name of this joint project is OSIS.


			     CONTACT INFO

Please, contact me about this application. I really would like to
receieve help, hints, patches, new implementations of TOS-calls,
etc...



Elias Martenson
elias@omicron.se