Greetings !

First: I'm on vacation for the next 2 weeks. So don't expect any answer
soon - not that I would write anything that deserves an answer anyhow...

> > And the other 4 bits of the first byte are the 2nd pixel in the first
> > line ? I have to ask, since I saw a lot of weird pixel formats...
> 
> Yep.  The VIDC is one of Acorn's saner creations.  Of course, it'd be nice
> if the rasops code could handle less sane devices as well.
That sounds reasonable enough. The endianness bit is a bit awkward still
but we may see...
 
> > > Other bit-depths work analogously.  If you're going to fix the rasops code, though, the first
> > > thing that needs doing is to make it properly endianness-independent.
> > Sounds awful but needs to be done.
> Yep.  And you need to allow for the CPU and the framebuffer being
> different endiannesses, and there being multiple framebuffers of different
> endiannesses installed at once and so on.  All good fun.
So what - we need to know what endianness the framebuffer expects and
code the rest in C-macros like hton and so on... would be bitchy to
debug but sounds rather straight forward... btw. I never saw a
framebuffer that disagreed with it's host CPU regarding endianness...
not that this would mean anything.

> > > Working out which screen mode is equivalent to the current one at a
> > > different depth is non-trivial, since it involves snarfing the mode
> > > database and reading through it.
> >
> > Well, there aren't that much screen modes, a simple table stored
> > somewherein BBBB should do the job, eg. it could warn if it finds a
> > "non-approved" mode, switch to the equivalent 8bit mode when possible (
> > since there is no 800x600 in 8bit )
> > As far as I know (please correct me if I'm wrong) there is only one
> > thing machine dependant, the fact that A5k-style machines had an
> > additional oscillator that enables 800x600 in 4bit.
 
> Actually two additional oscillators -- there's a 25.125 MHz one for
> 640x480 modes.  Anyway, if you want to code this, feel free.  I'm not
> about to, but I'll incorporate worthwhile patches.
I always thought that the a3k and the like where able to do 640x480 ? I
never had one...
Well, according to the manual my A5k knows about 37 screen modes. Most
of the time the 8bit mode is the 4bit mode +1 except 800x600. ( Sorry, I
don't have the manual in front of me... so I don't know the real
numbers. ) But it seems that most modes were - say, a="some mode with 1
bit colour" then a+1="same thing with 2 bits", a+2="4bit", a+3="8bit".
Should be pretty easy to do in BASIC. 

> > > Better would be to have the kernel change screen mode to something it can handle, but
> > > changing screen modes is mildly tricky (it involves actually thinking about DMA timings).
> > Hmm, when does the kernel seriously trash RiscOS ? Is there a stage
> > where it is still able to do RiscOS SWIs ?
> 
> RISC OS's exception vectors are trashed when we replace zero page in
> start.c, just before calling pmap_bootstrap.  The allocsys call before
> that might wipe something RISC OS needs, though.  I'd rather not add
> calls into RISC OS just to work around a rasops bug, though.  If you want
> to solve this problem, fix rasops.
OK, sounds like no SWIs from the kernel even in early stages.
 
> > Whold be better for me since I have a RARP/bootparam environment
> > running. But what does the kernel expect on the prompt it displays after
> > hardware probing when it should mount it's filesystems ?
> 
> If you type something it doesn't understand, it'll tell you
I didn't try...

> (who says Unix isn't user-friendly?).
I certainly don't.

>  You either want the name of a disc partition or of a network interface.
ok, so next time I type "ea0" and expect some RARP from the network
board ?
 
> > > > Sorry, can't keep it back - how hard is it to make the internal IDE on
> > > > A5k style machines work ?
> > > Should be easy enough, but I'm not trying it without the hardware in front
> > > of me.
> > I have an A4k with 4MB gathering dust, but without keyboard, mouse and
> > harddisk. Unfortunately it is in germany.
> Pity.  Such a thing would be very useful to me.
Hmm, it's quite possible that I take a trip to London this summer. I
could take the A4k with me but it isn't clear yet if the trip happens at
all. You don't possibly know anyone who comes to Berlin anytime soon ?
Maybe we find some kind of arrangement ( I would like to give it to
anyone who does anything useful with it - NetBSD development is
certainly one of the most useful things one could do with it ). You
would like it since it has an UK ROM. ( my A5k has the german version
which sucks like hell )

bye
Michael