Re: Handheld Hard Drives

Brian Smithson (starnet!apple!eitech.com!brian)
Wed, 18 Aug 93 15:15:48 PDT

I use a MicroSolutions BackPack 40MB hard drive on the parallel port
of my UL. It works OK, except that there is some interference between
the parallel port activity and the serial port interrupts. From what I
understand, the BackPack (and other vendors) driver needs to disable
interrupts during some portion of the transfer -- I guess that it's
necessary in order to distinguish between disk drive data and printer
data.

The interference between LPT and COM1 happens only when the disk is being
accessed, and so it's not such a big problem. The problem doesn't seem
to occur with the COM2 modem -- maybe because it's 2400 baud and therefore
has more relaxed timing requirements.

I had used another vendor's parallel port hard drive for a while before
I got the BackPack, and it had the same problem. I also talked to the tech
support people at Sysgen (yet another vendor) and they said that their
product wouldn't have that problem, but I didn't check it out.

The symptoms depend on what you're using the serial port for:

- When doing 9600 baud file transfers (e.g. with xmodem or kermit over COM1),
I get errors and retries but it recovers OK.

- When using a mouse (trackball, really) for Geoworks Ensemble, the cursor
movement gets a little erratic. Eventually, I became trained _not_ to
move the mouse when opening or closing a file on the BackPack :-).

- When using PC-Interface from Locus (which connects a UNIX filesystem to the
UL as a virtual DOS drive, albeit at 9600 baud via COM1), I didn't notice
any problems. However, it may have been getting errors and retrying without
telling me about it. Boy, there's a configuration nightmare for you:
drive A: is the floppy, B: is the ROMcard, C: is a small slice of the
silicon disk, D: is the internal ROM, E: is a Stacker volume taking up
the rest of the silicon disk, F: is the BackPack drive, and G: is a
virtual drive on the UNIX system!

So basically, I think the Handheld Hard Drive will probably work OK,
but you might have problems with serial interrupts on COM1. BTW, it's
really nice to have a hard drive on the UL. It's especially nice if
you want to install a large-footprint application on the UL and then
remove unnecessary files so that you can fit it onto the silicon disk.
Like Mad Man Muntz, for those who have heard of him...

-- 
-Brian Smithson                                          brian@eitech.com
 Enterprise Integration Technologies                      +1 415 617 8009
 459 Hamilton Avenue, Palo Alto, CA 94301 USA         FAX +1 415 617 8019