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Digger
Registered: Mar 2005
Posts: 448 |
$d011 trickery duplicated text lines
Does any one know the $d011 trick to repeat the first char row? I am trying to cancel badlines on the 8th line of each charline (between cycles 54-57) but it doesn't work. The first line gets duplicated but only twice. |
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ChristopherJam
Registered: Aug 2004
Posts: 1424 |
Yes, except it doesn't actually fetch the characters, so the internal row buffer remains unchanged. |
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Oswald
Registered: Apr 2002
Posts: 5127 |
ok while we're at it can you explain last row stretch with internal counters? I'm staring at the VIC article but the more I stare at it the less sense it makes. like RC is never incremented after reaching 7 by these rules:
"In the first phase of cycle 58, the VIC checks if RC=7. If so, the video
logic goes to idle state and VCBASE is loaded from VC (VC->VCBASE). If
the video logic is in display state afterwards (this is always the case
if there is a Bad Line Condition), RC is incremented."
so RC=7, we go to idle state, thus RC is not incremented hence it is only incremented in display state.
I'm thinking of stretching the last pixel row, to get the 8 high char line I want.
ok not possible hence my last is 7th not 8th, and that stretch only works on 8th.
only straw left is repeat 1st line but that adds only a badline, urgh. |
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Oswald
Registered: Apr 2002
Posts: 5127 |
ok I guess I get it, if *sometime later* there is badline then will we go back to display state and increment rc. whenever. |
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ChristopherJam
Registered: Aug 2004
Posts: 1424 |
Yup, exactly.
Lft's done a nice PDF of the timing, you can find it at https://www.linusakesson.net/programming/vic-timing/ |
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JackAsser
Registered: Jun 2002
Posts: 2038 |
Quote: Yup, exactly.
Lft's done a nice PDF of the timing, you can find it at https://www.linusakesson.net/programming/vic-timing/
Yes. Do read this. It takes a while to understand how to interpret it but once you learn it all VIC-tricks are easy to figure out. |
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Oswald
Registered: Apr 2002
Posts: 5127 |
already used this pdf, but not the how rc /vc works part, that still needs a lot of thinking :)
fex, I can not explain how/why last row stretch works. |
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Rastah Bar
Account closed
Registered: Oct 2012
Posts: 336 |
I noticed something strange, could someone explain this to me, please?
I create a badline after cycle 14 on every 4th rasterline, starting on line $30. I also opened the borders. In text mode you can see the memory wrap around: the last 5 rasterlines on the text screen start with the characters in memory locations $07e8 and so on, with colors from $dbe8 and so on.
On rasterline $30 the last byte from each character in $0400 ... is visible, but in the colors from $dbe8 and so on. This caught my attention since I expected the screen ram and color ram memory addresses to match.
If I do the same thing in hires bitmap mode, rasterline $30 now shows the colors from rasterline $f8, but in bitmap mode these colors are determined by screen ram.
So in plain text mode data from $0400 ... is shown in rasterline $30, while in bitmap mode data from $07e8 ... seems to be used.
I'm seeing this in VICE 3.5, Hoxs, and micro64. |
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Krill
Registered: Apr 2002
Posts: 3098 |
Quoting Rastah BarOn rasterline $30 the last byte from each character in $0400 ... is visible, but in the colors from $dbe8 and so on. This caught my attention since I expected the screen ram and color ram memory addresses to match. Both addresses should match, as they're coming from one and the same counter in VIC.
It seems like you're linecrunching right from the top of the screen. When you do that, there is no badline DMA in line $30 (otherwise you'd see the first, not the last, pixel row of the characters). Instead, whatever was put in the line buffer in the previous frame is displayed.
But colours and characters should come from matching addresses. Are you sure there is a mismatch? |
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Martin Piper
Registered: Nov 2007
Posts: 739 |
Perhaps a picture would help? :) |
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Rastah Bar
Account closed
Registered: Oct 2012
Posts: 336 |
Yes, there is a mismatch as you can see in the pictures in text mode and bitmap mode.
https://i.postimg.cc/qvLzbQ3D/text-mode.png
https://i.postimg.cc/WbsVWVwj/hires-bitmap-mode.png
The first character row $0400 ... $0427 is filled with inverse space.
Addresses $dbe8 .. $dbff contain 0,1,2,3,4,5,7,8,0,1, ...
Addresses $07e8 .. $07ff contain 0,0,ff,ff,ff,ff,0,0,0,0,ff,ff,ff,ff, ...
The first stripe in the right border is at line $2f |
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