[hatari-devel] spec512 using blitter on STE

npomarede at corp.free.fr npomarede at corp.free.fr
Sun Jan 10 20:40:49 CET 2010


On Sun, 10 Jan 2010, npomarede at corp.free.fr wrote:
>
> Thomas wrote :
>
>> Could that be related to the problem in the EPSS demo? That demo fails
>> to open the right border because there is also a blitter access between
>> the left and right border. The offset between wrong and right access
>> also seems to be 16 cycles if I got that right...
>
> Not directly, because they don't use the same 16 pixels trick (the screen
> is 160 bytes per line), but by comparing with Steem I can see that
> Video_CalculateAddress doesn't seem to be correct and return a value that
> is 8 bytes too low (which gives a 16 cycles shift).
> I will try to look at this too, as this doesn't seem to be a blitter
> problem in fact.
>

The problem is now fixed ; it was due to reading $ff8209 while $ff8265 > 0,
which scrolls the screen with prefetching. In that case, the shifter 
starts reading data 16 pixels earlier in the left border than the usual 
position, which means we should add 8 bytes to the content of $ff8209 to 
get the same result (it is considered to be a bad practice to read 
$ff8209 on STe while scrolling is used to get in synch with the shifter, 
but as it was used by this demo, we have to support it)

BTW Anders, this demo seems to use the same left/right border removal 
(224 bytes) as the one you used in the dhs demos : hi/lo is at cycle 504/4 
and there's no stabilizer.


Nicolas



More information about the hatari-devel mailing list