Re: vertical retrace inte

Thread View: rec.games.programmer

2 messages

[T] Back to Threads [V] Tree View [G] Group Articles

2 total messages Started by Secret Mud Tue, 11 Aug 1992 10:54

#573

Author: Secret Mud
Date: Tue, 11 Aug 1992 10:54

19 lines
1097 bytes

From: tmkk@uiuc.edu (Khan)
 ... trimmed ...
>
>Voila! Shared interrupts. All it takes is a little intelligent design on
>the part of the programmer. The REAL problem is that apparently few
>programmers go the "extra mile" and design ISRs that a) interrogate the
>hardware to see if which device generated the interrupt, and b) chain to
>prior handlers if their device was not responsible. But don't think for
>a minute that because it's not commonly done that it CANNOT be done at
>all.
>

It's not that simple.  The problem lies in the actual interrupt signal.
Almost all cards drive the line high or low, rather than using a pull up
resistor and driving the line low.  So if two cards try to share an interrupt,
they would end up fighting, with one card driving high, and the other driving
low.

A definite 11 year old design fault.

Re: vertical retrace inte

#585

Author: Dave Stampe-Psy+Eng
Date: Tue, 11 Aug 1992 21:45

19 lines
1361 bytes

>It's not that simple.  The problem lies in the actual interrupt signal.
>Almost all cards drive the line high or low, rather than using a pull up
>resistor and driving the line low.  So if two cards try to share an interrupt,
>they would end up fighting, with one card driving high, and the other driving
>low.
>
>A definite 11 year old design fault.

You bet!  They don't even have a pullup resistor on the motherboard,
so you can't just add diodes or open-collector gates to share the lines
(I've tried).


--------------------------------------------------------------------------
| My life is Hardware,                    |                              | 
| my destiny is Software,                 |         Dave Stampe          |
| my CPU is Wetware...                    |                              | 
| Anybody got a SDB I can borrow?         | dstamp@watserv1.uwaterloo.ca |
__________________________________________________________________________

Thread Navigation

This is a paginated view of messages in the thread with full content displayed inline.

Messages are displayed in chronological order, with the original post highlighted in green.

Use pagination controls to navigate through all messages in large threads.

Back to All Threads