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Atari coding BBS
 
Re: HBL on Falcon (follow up)
Posted by: Orion Apr,12.2019-00:30 


Here are some more details coming from additional investigations:

1) In RGB mode, the behavior is close to that of the ST, although it is more difficult to "hide" the interrupt jitter.
In particular, in this mode, the Timer-B/HBL is triggered as expected and the ST palette can be changed anywhere in a raster line.

2) In VGA mode, things are totally different.
As far as I understand, there are two mechanisms which impact the Timer-B/HBL behavior and the way color changes are handled:
a) In VGA / ST-Compatible mode, the VIDEL is configured to double lines.
b) With the VIDEL, every raster line is divided into 2 (horizontal) halflines.
The consequences (I observed) are the following:
- the Timer-B/HBL is triggered at the beginning of the second (horizontal) halfline (in other words, in the middle of the screen).
- The palette cannot be changed anywhere in a raster line: when a color is changed while a raster line is displayed, that change may be taken into account or may be ignored.
- It is possible to change colors in the middle of a "doubled" (vertical) raster line.

Is it possible to use VGA in ST-Compatible mode to run ST games or demos which play with the HBL for palette changes or to display rasters?





[All messages in this thread]

Topic Posted by  Date 
HBL on Falcon (follow up) Orion Apr,11.2019-18:59
  Re: HBL on Falcon (follow up) Orion Apr,12.2019-00:30
    Re: HBL on Falcon (follow up) mikro Apr,12.2019-09:08
      Re: HBL on Falcon (follow up) Orion Apr,12.2019-11:50
        Re: HBL on Falcon (follow up) Daniel Apr,15.2019-00:09
          Re: HBL on Falcon (follow up) mikro Apr,15.2019-11:46
            Re: HBL on Falcon (follow up) Orion Apr,15.2019-15:12
        Re: HBL on Falcon (follow up) evil Apr,15.2019-11:46
          Re: HBL on Falcon (follow up) Orion Apr,15.2019-14:39
            Re: HBL on Falcon (follow up) mikro Apr,16.2019-07:43
              Re: HBL on Falcon (follow up) Orion Apr,16.2019-12:20
          Re: HBL on Falcon (follow up) Daniel Apr,16.2019-23:45
            Re: HBL on Falcon (follow up) mikro Jun,16.2019-14:26


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