Subject: Re: ARM platforms
To: None <>
From: Andy Ball <>
List: port-arm
Date: 07/12/2002 01:07:39
Hello Alan!

  AB> ...Or what kinds of features one might want to have on
    > such a thing.

Now that I /can/ answer ;-) Each of the projects I'm working
on have slightly different IO needs, but most could be
driven by a common core.

I suspect (but have not yet proven) that a 50MHz ARM could
meet a lot of light-duty needs: things like remote access
servers and dial-up routers where the bottleneck is the
communications link rather than the processor.

Perhaps I'm an old fart in this respect, but I like to see
serial ports on gear.  The other day I was helping a friend
arrange mobile access to the Internet.  Because his phone
had been designed to pretend it was an ordinary analog modem
at the end of a serial cable, his sub-notebook (that doesn't
have a PC-Card slot, and almost certainly wouldn't run
proprietary driver software) should be able to connect from
the field via his digital wireless network (when he receives
the serial cable for his phone).  I observed to him at the
time that the glue making our end of this possible was a
serial port standard layed down in the 1960s.

Some form of standard expansion slot is a good thing.  A
single type III PC-Card slot lets me plug in more serial
ports, an analog modem, ethernet, wireless ethernet, mobile
Internet (CDPD, GPRS etc), a SCSI bus, Flash, SRAM or hard
disk storage... the list goes on and the installed base of
PC-Card slots make some of these inexpensive options.

An ISA slot gives me similar options.  A PCI slot adds
bandwidth for more demanding applications.  Come to think of
it, a 3.3V 32-bit PCI slot might not add a lot to the whole
system's power consumption.

So, all this waffle boils down to:-

  * An ARM at not much less than 50MHz

  * Some memory, hopefully a SIMM or DIMM socket
      (I'm guessing that a DIMM can be used to provide two
      32-bit banks of RAM).

  * Room for plenty of ROM, perhaps Flash.

  * At least one serial port, preferrably two.
      The RS-232/RS-422 debate is left for another day, but
      buffered UARTs like the NS 16550A help lighten the
      interrupt load.  The console might get away with just
      3 wires, but a second serial port should support full
      hardware flow control.

  * An expansion slot.
      ISA or PCI could go into static equipment.  PC-Card
      could go into both static and mobile equipment.

(feel free to add Ethernet and SCSI if you're feeling
 adventurous ;-)

I'm looking for bare boards. Some of my projects are network
related, so they could go into a 1U rack mount case or slide
into a rack-mounted cardframe.  I happen to manage some
networks, and find it irritating when I have to go out and
buy shelves for network gear that's in odd-shaped, cheap
plastic boxes.  More frustrating in some cases is the RF
interference that radiates straight through the plastic. :-(

  AB> I mean, how much could a device that would fit in the
    > palm of your hand really cost?  [Don't answer that...
    > I probably don't want to know...]

I couldn't match the volumes of a PDA vendor like Compaq
(er...HPaq?), so it would be a real struggle for to match
the price of their iPaq for example.  For many mobile
applications, it's probably cheaper to just buy a whole PDA
or palmtop and plug things into that.  One more reason to
appreciate the efforts of those people who have made NetBSD
work on PDAs and palmtops.

  - Andy Ball.