Loadable device drivers...in V.4?

[Chris Torek]

In article <35110 at cup.portal.com> ts at cup.portal.com (Tim W Smith) writes:
>I wish vendors would do this.  It's not even hard. ...
>First, you need a system call that will allocate kernel memory
>for the driver.  Second, you need a system call that will install
>an interrupt handler for the driver.  [Do everything else in user code]

It is not (always) this easy.  On some machines, you must use particular
memory regions for particular devices, and they may already be in use.
Not all machines use interrupts, either; the `install' call must have
more information than just an interrupt vector.  The first problem is
really the hardest, though, and usually means everything critical must
be allocated at boot time.  (Even VAXen, which are notorious for allowing
sloppiness, sometimes require special memory, e.g., for Unibus vectors
on 750s---these must appear immediately after the SCB [you could copy and
then move the SCB, of course...]---or for some Unibus devices [need 16-bit
addresses].)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 405 2750)
Domain:	chris at cs.umd.edu	Path:	uunet!mimsy!chris