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From: vlrugvg@dutrun.UUCP (Ge van Geldorp)
Newsgroups: comp.unix.aix
Subject: PS/2 device driver docs
Summary: Appendix C stinks
Keywords: AIX 1.1, device driver
Message-ID: <1517@dutrun.UUCP>
Date: 31 May 90 20:13:40 GMT
Reply-To: ge@dutlru2.tudelft.nl (Ge van Geldorp)
Organization: Delft University of Technology, The Netherlands
Lines: 39

I'm trying to write a device driver for AIX PS/2 1.1 and find the IBM
documentation (Appendix C of the Technical Reference) less than clear.
Sometimes the documentation even seems to lie:
 - It says to compile the driver with the command `cc -c -DKERNEL -Di386
   driver.c'. You better add a `-I/usr/include/sys' to this.
 - The discussion of `ddopen' says the `oflag' argument of the open(2) system
   call is passed as the `flag' argument to `ddopen'. Most of the bits
   get passed unmodified, however, the O_RDONLY flag has the value 0
   when passed to open(2), but `ddopen' receives a value of 1. O_WRONLY
   and O_RDWR also exhibit this behaviour.
 - subyte() is documented to return 0 if the address at which the byte
   is to be stored is valid, -1 otherwise. It seems that subyte()
   actually returns the byte which it stored (i.e. the `c' parameter).

I looked around /etc/master to find an unused major number. My system
had major values in the range 0-49, so I picked 50 as the major number
of my driver. This resulted in lots of `no such device or address'
messages. In dispair, I tried 19 as my major number (19 was not used in
the /etc/master file). Presto, end of problem. Does this mean there is a
hard-coded maximum major value of 49 somewhere? If so, is this
documented anywhere?

Suppose (well, don't suppose, I actually do this) I tell an adapter to
do something, then go to sleep, to be waken up from an interrupt
routine. Is there a race condition here? I.e. if the adapter immediately
generates an interrupt before the user-context routine goes to sleep,
will the wakeup() specifying a channel for which there is no correspon-
ding sleep() yet be discarded or will the information be saved?

Could someone please provide an example of the use of the physio()
routine? The 2-line explanation in the documentation is not sufficient
for me to determine how to call this routine.

Thanks.


Ge van Geldorp
ge@dutlru2.tudelft.nl
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