"Big" screen, flickering, "R: "/"Z:", etc

"Big" screen, flickering, "R: "/"Z:", etc

Post by Frank E Seip » Sat, 31 Aug 1991 05:41:35



 First, I was experimenting with display lists a couple days ago and found
that I could add 5 Graphics 0 lines to the top or bottom of a graphics
0 display. Thus it would seem possible to have a 29 line text display on
the 8-bit, by adding several 2's to display list and eliminating some of
the blank scan lines (112's) at the beginning. (On some TV's it might only
be possible to get one or two lines. Five seems to be an absolute
maximum; the screen flickers when I attempt to add more than this).
 I am able to use these lines with special programming (I put their screen
memory on page six). But I would like to just use them as an extension of
the normal 24 line display. What modifications to E: would be required,
and how easy would it be on an XL/XE (could I just copy the OS into RAM
and change a couple of bytes?)
 Second, how does one avoid the flickering which occurs in a Display List
Interrupt (DLI) which changes the background color of the screen? I am
talking about flickering during disk I/O. It appears as if the DLI's are
disabled when data is being transferred over the serial port.
 I am working on a BBS program and am looking for one of those old "dual"
handlers which, when PRINTed to, outputs to both screen and modem. Anybody
have one of these? I could also use some short m/l subroutines callable
from BASIC to do such things as send a file to R: (text mode with ^S,
^X support).
 Finally, I have a working BBS program which can handle USENET newsgroups,
as well as several other base types. It is read-only, but works reliably.
It can handle 62^2 messages per base with MyDos, and 125^2 with Sparta.
It is in BASIC XE. If anybody's interested I can send them a copy. It is
missing a lot of basic features at this stage, though. Still it is somewhat
interesting; made for a hard drive system, it creates a subdirectory for
each user. The user data, message base info., e-mail, f-mail, etc, is
(or will be for some of those!) stored in this directory. This allows for
more free form user data, no fixed-length records. Of course it also has
a high overhead for all those directories, but it seems to work well.

 
 
 

"Big" screen, flickering, "R: "/"Z:", etc

Post by Norman L » Sat, 31 Aug 1991 09:31:07



Quote:> Second, how does one avoid the flickering which occurs in a Display List
>Interrupt (DLI) which changes the background color of the screen? I am
>talking about flickering during disk I/O. It appears as if the DLI's are
>disabled when data is being transferred over the serial port.

I've got no solution to offer, but hopefully this explanation will help.
I don't believe DLI's are disabled during disk I/O; rather, it's the deferred
mode VBI's.  The deferred mode VBI's are disabled during critical I/O
sections, and this could account for the flickering you mention; copying
of screen colors from shadow locations (e.g. 710, 712) to hardware
locations is done during the deferred mode.  When the flickering occurs,
which color takes precedence; the value in the shadow location, or the
value you're stuffing in the hardware register?

--Norman Lin


 
 
 

"Big" screen, flickering, "R: "/"Z:", etc

Post by Doug Woko » Sun, 01 Sep 1991 04:40:30




>> Second, how does one avoid the flickering which occurs in a Display List
>>Interrupt (DLI) which changes the background color of the screen? I am
>>talking about flickering during disk I/O. It appears as if the DLI's are
>>disabled when data is being transferred over the serial port.

>I've got no solution to offer, but hopefully this explanation will help.
>I don't believe DLI's are disabled during disk I/O; rather, it's the deferred
>mode VBI's.  The deferred mode VBI's are disabled during critical I/O
>sections, and this could account for the flickering you mention; copying
>of screen colors from shadow locations (e.g. 710, 712) to hardware
>locations is done during the deferred mode.  When the flickering occurs,
>which color takes precedence; the value in the shadow location, or the
>value you're stuffing in the hardware register?

        DLIs are _not_ disabled, as they are NMIs (Non-Maskable Interrupts)
and _cannot_ be simply shut off.  What's happening is that during disk I/O,
the VBI routine that copies the shadow register color to the hardware register
can't run.  Normally, this doesn't cause a problem, but if you changed the
color in midscreen, a la DLI, the next screen will begin with the color used
at the end of the previous screen.  What might work: set up a DLI at the
very beginning of the screen, before anything is displayed, to change the
color.  This will render the shadow register useless, but will prevent most
of the flickering associated with disk access.  Sometimes, keypresses and
other interrupts can delay the DLI enough to cause a slight 'shiver' when
the DLI occurs a line or two late.  This is normally not very noticeable.
Hope this helps...

--
        Doug Wokoun            /      /                | If you don't

            |||                   L     (((( STe ))))  | you will
    Atari  / | \  S I G         \___/                  |  fall for anything.

 
 
 

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