slackey@bbn.com (Stan Lackey) (12/28/88)
I have finally done my first DLI <yawn> so what's the big deal? Well - I first did the following. I changed the display stuff at some point on the screen, to change the color registers and the character set, and relied on the built in vertical blank routine to change them back for the top half of the screen again. Well, it seems like CRITIC gets set a lot more than I expected, as there was a lot of flicker on the to half. So, I made an addition to the first stage VBI to set the character set and colors back all the time. I still get some flicker (it seems to miss either interrupt from time to time, say once every 10 seconds)! Is this a reality in the Atari, or did I not set something up right? -Stan
brett@sylvester.umd.edu (Brett S Bourbin) (01/06/89)
In article <33887@bbn.COM> slackey@BBN.COM (Stan Lackey) writes: >I have finally done my first DLI <yawn> so what's the big deal? >Well - I first did the following. I changed the display stuff at >some point on the screen, to change the color registers and the character >set, and relied on the built in vertical blank routine to change them >back for the top half of the screen again. Well, it seems like >CRITIC gets set a lot more than I expected, as there was a lot of >flicker on the to half. So, I made an addition to the first stage >VBI to set the character set and colors back all the time. > Well, like you said, the VBI CRITIC flag is there for a reason. It is needed for the OS I/O routines. Stealing the first stage VBI and doing some hardware poking, then vectoring to the second stage is your best bet. Just remember that during the horizontal blank (DLI), you only have enough time to change one or two registers after the WSYNC. The _Big Deal_ about DLI's is what you can do with them. Sure, everyone today can change the colors of the screen midway down and change the character set pointer. But the DLI is more than that. I have used the DLI in the past to simulate a 3-D scrolling maze, where the VBI created a custom DLI each time the player moved. I also have created a "virtual sprite" system with the use of the DLI which allows many, many more sprites than the 4 hardware limit. Just some food for thought. --Brett S Bourbin __ __ _ __ _ Instructional Computing Programs -- Univ of Maryland | || | / || || \ | || || || || | INTERNET: brett@SYLVESTER.UMD.EDU | || || || || | bbourbin@UMD5.UMD.EDU \_||_/ |__||__||__| BIX: brettb College Park BITNET: bbourbin@UMDD