Atari-Forum

You can try it with Hatari devel version and it will be included in Hatari 2.3 I have done some tests and it seems that Hatari is very accurate now versus real HW for this blitter aspect ... but not the way I would have hoped ! :lol: Let me explain. In the screen I am coding, I encountered a bug wi...

Great !!!
I'll try this with the develop version soon.
Thanks Nicolas.

Anima wrote: ↑Thu Jul 30, 2020 8:19 pm After two more runs it seems that the issue has indeed been fixed by replacing the CPU.

Maybe this CPU did not want to admit defeat versus the blitter

If you consider yourself as a n00b or if you need to deal with interrupts, then maybe the preshifted technique mentionned by thomas3 few posts above would definitively be simpler ;-) But if you really want to dive into the syncscroll, you can also start with Alien's articles. Part 1 and 2 start with...

And the ST Synclock demosystem by evil from DHS provides some ready to use code.
https://dhs.nu/files.php?t=democreation

On ST, you cannot do a vertical scroll as simply as you can do on STe by changing the screen address. You have to use the syncscroll technique that is not so obvious. If I remember well there should be several posts in the forum that describe how it works.

Ok, so I'll let you finish it ! Your modifications will be far more accurate than mine !

Ok thanks for the explanation ! I'm going too look further in Hatari code then !

Uko took some time to look at Hatari's code and sent me a patch to fix the condition where NFSR was incorrectly used to trigger a read-write-modify operation (instead of just relying on the endmask). So current Hatari devel version should now have correct number of cycles when blitting with Uko's e...

Just an idea, difficult to say without looking at the whole code: The synccode that you are using only works if the low byte of the video counter at the beginning of the line is equal to zero, i.e. the address of the begin of the line if multiple of 256. For your timer A syncscroll, you are at the b...

mrbombermillzy wrote:@uko: Thankyou. Thats very kind. I would like to take a look at what you have. It sounds very useful.

Ok, here it is !

If it may help, I have made a Python script that allows to load an image, to display it, to display number of colours (global or per line), to reduce the number of colors (global or per line) or to split each line and to allow to reimport them. It also can generate the picture (binary format) and pa...

But finally the method I have used is to split the picture in multiple one line image files, then use XnView to convert each line file to x colors (using the batch converter and selecting one dithering method), then reassembling the converted files. So this weekend I wrote a little Delphi tool to s...

Playing a 9600Hz digi-sound means the replay routine should be executed 192 times per VBL. Changing the palette every line means changing it 200 times per VBL. If you use interrupts for both the replay routine (Timer-A) and the color changes (HBL), it will be difficult to avoid interrupts jitter (l...

Hi, I have never tried the tool mentionned by joska, but it seems interesting ! On my side I have used home-made converters to achieve this. I have tried the method you have in mind, Arne, but it provided worse results than simply reducing the bitdepth for each color until you have a maximum of 16 c...

fenarinarsa wrote:Don't forget that on Mega STE the blitter takes 4 extra cycles to start

I think Leonard had to take this into account for "We Were@" to work correctly on Mega STE.

Thanks for the info, I'll have to think about that !

npomarede wrote:Hopefully, I will be able to fix this in a near future

Hopefully I'm a slow coder and it will take me a long time to finish my screen !
Thanks.

I will have a look at this case ; I have some work in progress to fix some wrong cases where xcount=1 (as Ijor described them to me) and not many time at the moment. I will see if this can be fixed on current code base or if this needs to be part of the rewrite I'm planning to do. Hi ! Thanks for y...

Everybody is wrong in this case. If XCOUNT is set to one, Blitter doesn't fully honor the NFSR bit and performs a final source read regardless. It might be considered a Blitter buglet, but you shouldn't need to use NFSR if XCOUNT is one. In the post describing the tests I have performed, when I tal...

Hi could you provide the executable in your zip archive ? My STE is currently not available (still packed after recently moving home), but maybe some other people here could run your tests on their STE. Nicolas No problem. The source needs to be recompiled to change the test parameters, but I have ...

Hi! In order to make things clearer (at least for me !), I have written a little test program to perform some tests and count the number of memory accesses performed by the blitter. The source code is included in the zip file attached to this post. This program blits a one bitplane rectangle onto th...

How it would be useful to enable NFSR without a mask ??? In very limited cases... But imagine you have a background using only 3 bitplanes, and a one bitplane sprite of size 16x200 to move over (and of course accurate palette settings). In this case, when you set both SKEW and NFSR, you don't mind ...

It is true that there is no much point in using NFSR without a mask. But (if for some reason) NFSR is set and the active mask is $FFFF and the OP mode doesn't require the original dest data, then Blitter doesn't perform a destination read. It may be useful if you use bitplanes as layers, with 16 pi...

Nicolas, Thanks for pointing the Hatari source code, I'll have a look to it. I am quite surprised that masking does not add additional cycles, and it seems that in my attempts (but I must check again of course), Hatari uses more cycles when mask is not $FFFF. But I am in the case where XCount = 1 (i...

Hi ! Up to now I have mainly used the following table to estimate the blitter execution times for sizing my code (and also the Blitter FAQ from The Paranoid of Paradox): http://retrospec.sgn.net/users/tomcat/miodrag/Atari_ST/Atari%20ST%20Internals.htm#BLITTER These timings seem OK as loong as SKEW, ...