PDA Squeak (especially Palm III)

Maloney johnm at wdi.disney.com
Sat Sep 26 01:16:21 UTC 1998


At 11:37 PM +0200 9/24/98, Carsten Haerle wrote:
>...
>The problem with the PalmPilot is that you don't have 32bit linear address
>space when you use the standard OS. Replacing it with Linux and running
>Squeak on it is really an interesting technology demonstration but not
>the thing most people want to do with the Pilot.
>
>So we need 16 bit VM for Squeak also. Having this would enable other
>PDA ports as well (I don't think all PDAs have an 32bit flat memory model),
>and it would make the image smaller which is interesting in the low mem
>situations for PDAs.
>
>It should not be too difficult, as the original blue book proposed a 16bit
>VM and the Squeak VM followed the blue book very closely. I would like
>to see the clean interfaces to the object memory and the special code which
>assumes 32bit intergers factored out, so I have the abstract interpreter and
>lets say two subclasses which are named Interpreter16 and Interpreter32.

We diverged farther from the Blue Book in the area of the Object Memory
than in other aspects of the design. For example:

  a. Squeak uses direct pointers, not object table indices
  b. Squeak uses objects headers designed for 32-bit words
  c. Squeak's generational scavenger assumes a large, linear
     address space so it can use a simple address comparision
     to tell the difference between young and old objects

However, I know of several object memorys designed to work well
within a collection of 32K memory segments, including one
designed by Mark Lentczner of Glyphic and one designed by
Antero Taivalsaar (sp?) at Sun Labs, so it's certainly
possible. But note that it isn't absolutely mandated by the
Palm Pilot hardware architecture; the 32K memory segment
limitation is entirely an artifact of their OS that I believe
could be worked around with far less effort than it would take
to build a new object memory (see Mike Wirth's messages to the
Squeak list on this subject).

If you're interested in actually writing Squeak code on the
Pilot, you might be disappointed even if you had a VM than
ran on it. There just aren't enough bits on that screen for
programming, and the processor is not fast enough to make up
for the lack of screen real estate. (If you have a fast processor,
you can do things like rapid window popup/iconification to
quickly shift tasks.)

That's what I imagine, but I'd be delighted to be proved
wrong. I love the design of the Pilot OS and would love to
have one with Squeak inside it.

However, the new flock of WinCE 2.0 machines have a bit more
memory and processing power, and larger screens; one of them might
make a lovely Squeak platform. For example, the Phillips Nino looks
pretty slick. Since I don't like the WinCE applications, if I had
one of these devices running Squeak I'd build my own address book
and date book apps in Squeak and would seldom ever touch WinCE.

	-- John





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