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[lcdproc] Trouble using FreeBSD and HD44780 drivers


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  • From: benjamin_tse AT agilent.com (TSE,BENJAMIN (A-Australia,ex1))
  • Subject: [lcdproc] Trouble using FreeBSD and HD44780 drivers
  • Date: Fri, 8 Jun 2001 15:49:10 +0800

> > The connection initializer then gets permission for any
> _extra_ ports
> > that that particular connection requires. We already have
> permission for
> > the base port address so the serialLpt driver and winamp
> drivers don't
> > need to gain permission to it again.
>
> I've been wondering why you choose to do it this way ? Why not just
> always reserve all three standard port registers ? Were you thinking
> about one application (lcdproc) using the output-pins and an other
> application using the input-pins ? I wouldn't mind reserving them all
> at once. Gives more transparent code anyway.

G'day Joris,

Your point is well taken, I agree that we might as well reserve all
addresses at once. Now that someone else has read the code :-) I think that
my original thoughts (outlined below) should make way for more maintainable
code.

The general principle that I used was to only do what was necessary. Every
connection type uses the base parallel port address so (at the time) it made
sense to get permissions in the generic connection initializer. Not every
driver uses all three registers so I didn't see the need to get permissions
for all three.

The decision had nothing to do with using multiple applications - getting
permissions to the port address doesn't stop other processes from also
getting access to it. Indeed this is happens with the ext8bit interface as
lcdproc drives the lcd whilst portato drives the led bargraph. Both
processes use the same port addresses and a semaphore is used for access
control.

Cheers,
Ben



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