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From: U613127@HNYKUN11.BITNET (Olaf Seibert)
Newsgroups: comp.sys.amiga
Subject: Re: serial port expansion
Message-ID: <8802042325.AA08851@jade.berkeley.edu>
Date: 4 Feb 88 21:45:28 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 44

I have another idea regarding extra serial boards.

Just create a utility to dynamically permutate the unit numbers of
several serial ports.
If you use a program that only knows about unit 0: Fine, give the port
you want it to open the number 0 and start the program.
If you have another such program, just swap unit numbers and the second
program can also have unit 0, but another one. Just make sure the
serial IO requests are properly initialized, so the IO requests can
be related to the correct physical port.  This means that different
ports should have unique device pointers, or unique unit pointers,
even if their unit NUMBERS are nor unique. [ I do not have the RKM
handy, but I think you get Unit pointers in your serial IO
Request. If only the unit number makes it into the Request, the juggler
can change the 0 in it to the real unit number ]  In any case, no serial
device driver needs to be changed to support this juggler, whether it
supports only one unit, or more than one.
You can also have the option to make the jugging automatic. That could
mean something like: If you open unit 0, you get the first available
unit. This is of course only suitable for programs that keep the
port open all the time they may need it, and close it only after
they are all done.
After some time, all programs know that there may be more than one
serial port, and that they may even have a name other than serial.device,
and you can dispose of the unit number juggler.

How about this?
Pro:*No change necessary in existing programs.
     Only the juggler needs to be aware of the file names for the different
       port drivers. Of course, it would be best if one driver drives
       all ports.
    *If done properly, no preloading needed of drivers OR resident lists.
    *I don't have to read ununderstandable pages like 'AllcoConfigDev'
     or something like that.
    *The juggler is optional, but can be kept even when no longer
     needed.

Con:*Propably the juggler needs to juggle with the list of devices.
    *Maybe it can install a fake serial.device ahead of the real one
     to catch all OpenDevices.
    *Maybe it is a little tricky (read: dirty), but its need is not permanent,
     unlike some other proposals.
    *I don't have a modem, a private phone nor a >1st serial port.

Olaf Seibert.