Re: ANNOUNCEMENT: Web page for TCP/IP for the Apple IIgs

[taubert@ux7.cso.uiuc.edu (Derek Anthon Taubert)]

John Le Febvre <John@klatch.demon.co.uk> writes:
>Wow!  Anyone checked out this site yet?  There's even a PC ISA to GS interface
>board mentioned, with Derek using a 3Com 3c503 ethernet board in his GS!.
>Are there any limitations on such an interface, any class of cards which 
>definately wouldn't work..?  Possibilities are endless...

Looks like I need a web page for this as well!  :)

I don't want to give out too much info about this just yet, but let me give you
a better idea of what is going on.  Remember, this currently is an 8 bit only
ISA slot, so 16 bit cards won't work (future plans, tho).

The only thing that isn't (currently) supported on the 8 bit slot is DMA.  I
could slap a standard PC DMA controller and some memory on there if it became
really necessary, but most cards have the ability to access all of their
functions without requiring DMA.  Note that DMA on the 8 bit ISA slot and DMA
in the GS are completely different things (GS DMA is bus mastering) so it's not
really as hard as most think to support.  In fact, I could do something really
cool like disconnecting the busses and allowing the PC DMA to work while the
GS kept churning.

I've placed a standard PC interrupt controller on the ISA interface, so all
of the IRQ lines are supported just like in the PC.  I've even modified GNO's
Serial Init Manager to understand the controller and negotiate access to the
vectors.  It checks the controller in the main interrupt handler just like
every other interrupt source on the GS, so it is rather elegant.

The interface runs off the processor slot, so it is possible to do I/O faster
than the 1MHz limitation of the normal slots.  You currently can't get this
because I have the BCLK running at 7MHz, and all of the ISA cycles use the
PC standard wait states.  However, if I ever work on a 16 bit slot that
supports zero wait states, you'll be able to do I/O at 2.8MHz or at least
1.4MHz.  Cool, eh?  :)  Actually, if I do the DMA thing (above) I could set
it up so you could access the extra memory at 2.8MHz no problem.

As far as cards that work in it, I've used a standard 16550 serial/parallel
card in it just fine, and a NE1000 ethernet card also.  I don't see any reason
why just about any 8-bit card shouldn't work.  Sound cards, drive controllers,
IDE controllers, internal modems, etc...

I'm fairly convinced that most cards will work, because I had to design this
thing very carefully in order to support wait states.  The ethernet cards
I'm using request additional wait states, and this was a REAL pain to get
right.  Since the ISA slot is asynchronous and the GS is very synchronous, I
had to use the RDY signal to accomplish this.  This unfortunately messes up the
TWGS completely.  If somebody would like to loan me a ZIP, I'd love to see if
it would work with that.

So, is it clear as mud now?  :)

Derek Taubert                    |
taubert@uiuc.edu                 | Ask me about TCP/IP for the Apple IIgs!
http://www.ceg.uiuc.edu/~taubert | Really, I'm serious!
FAX:(217) 359-0010               |
GS/TCP info: http://www.winternet.com/~taubert/gstcp.html