Tobias Fröschle wrote, on 16/Mar/13 19:15 | Mar16:
Am 16.03.2013 um 17:16 schrieb Dave Park:
Hi all,
It's been mentioned that vanilla QDOS/Minerva doesn't run happily on
68EC020 due to CPU differences. The GC/SGC copies and patches the OS to
work with the EC020 CPU, and to relocate certain resources.
My questions are: what are the differences? How does the GC/SGC boot the
unaltered OS to copy the OS to the GC to reboot with the patched version?
I tried reading out and comparing the SGC patched version, but I don't have
the knowledge to read what is an '020 change and what is a change for moved
locations of resources.
I would like to prepare a version of Minerva 1.97/1.98 to run specifically
with the 68EC020 system I'm building, and it could solve a lot of other
problems in the future for me.
Any pointers would be gratefully received, as currently, my 68EC020 hobby
project locks up a lot, and it's hard to fault trace a hardware issue if
there may be a firmware issue;)
--
Dave Park
Sandy Electronics, LLC
[email protected]
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Dave,
in my opinion, Minerva should be able to get along with an 68k20 happily. I
have seen comments in the sources that indicate that.
Vanilla QDOS, however, will most probably not run properly.
The main differences in a nutshell are:
- Exception stack frame looks different, so code that looks into the stack will
most probably miss the target
- Access to the SR (status register) and some other control registers is
privileged and can only be done from supervisor mode (I guess that is not
relevant to the OS as such because that runs in SV mode most of the time
anyways, but to applications)
- The 020 has some more registers (like VBR) that need to be initialized on
startup
- the 020 has an instruction cache - but that should not lead to problems with
code run from ROM, as that cannot be very self-modifying ;)
The rest of changes is additions to the 68k - If not used, should not matter.
Wasn't the ROM copied to RAM, patched, and run from there?
Tony
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