On Tue, Apr 25, 2000 at 03:28:59PM -0700, Steve Sabram wrote:
> Michael Sokolov wrote:
>
> > Dragonball lacking a virtual address-translating MMU. Does ARM have an MMU and
> > virtual addresses? If it does, you will simply forget about all these
> > contortions and program like on UNIX.
>
> NOOOOOOOOO!!!!!!!!!
> Virtual memory would kill everything that makes a Palm perform well
> at this price point. This is the primary reason why WinCE
> performance is so poor. If you need something like that, do a
> wireless LAN link to a server and just have the handheld access it.
So that's why they have CF card slots - they need somewhere to keep
the swapfile :).
Actually I disagree here. WinCE performance is poor because there are
a lot more layers between your call and the pixel on the screen, and
the data structures passed and worked on between them are bigger.
The virtual stuff isn't the cause (a 4Mb 386 was quite happy with
Linux 1.2 - they still make great disposable routers).
But NOT having a multithreaded UI layer (i.e. no clone() calls) is
part of Palm's elegance. It adds almost nothing to a WinCE device (I
could leave a terminal session receiving data and check memos, but
that is about it and Palm doesn't preclude it but does make it
difficult).
What a VM or MMU would give you is a real DmWriteCheck, and the
ability to use more than 8-12 Mb within card 0's addressing space.
For the most part the apps would ignore it, but the address seen by
the app might be virtual and you can avoid some heap fragmentation
problems. In that sense you would have a level of hardware heap
management.
But to clarify what I posted before, a true MMU would be overkill,
though a restartable bus error and other CPU32 or 68010 core features
would be desirable and give a lot of bang for the amount of the
change. (Or an onboard dma copy unit, again for things like DmWrite -
to do ultrafast memcpy, memset, and memcmp calls and their str
versions).
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