Double Pal Question

sandruzzo · 08 July 2017, 21:12

If I'm right, I've read that with doublepal dma cicles will double. Is that correct? How is possible?

Toni Wilen · 08 July 2017, 22:07

No.

Double mode = scanline length is halved, number of lines is doubled. Number of DMA slots stays about the same.

ross · 08 July 2017, 22:13

Quote:

Originally Posted by sandruzzo

If I'm right, I've read that with doublepal dma cicles will double. Is that correct? How is possible?

DBLPAL->double h-frequency->double data to fetch in same time frame->double DMA cycles used

What are your doubts?

[and yes, as Tony said logically the DMA slots stay the same
only differently distributed
I've checked in WinUAE HTOTAL=$79 VTOTAL=$24D
In PAL we have HTOTAL=$E2 VTOTAL=$137($138)]
]

Cheers,
ross

sandruzzo · 09 July 2017, 17:03

Quote:

Originally Posted by ross

DBLPAL->double h-frequency->double data to fetch in same time frame->double DMA cycles used

What are your doubts?

[and yes, as Tony said logically the DMA slots stay the same
only differently distributed
I've checked in WinUAE HTOTAL=$79 VTOTAL=$24D
In PAL we have HTOTAL=$E2 VTOTAL=$137($138)]
]

Cheers,
ross

I've read that some chip like Paula run faster

ross · 09 July 2017, 18:23

Quote:

Originally Posted by sandruzzo

I've read that some chip like Paula run faster

Paula work every time at the same frequency (CCK).
But sample periods can be minor due to more frequent DMA 'recharge'.
It's directly related to HTOTAL: everytime H counter wrap we have two sample per channel that DMA can load
(i've semplified, the concept is that).
Smaller HTOTAL greater Paula reproduction frequency possible

Ciao,
ross

sandruzzo · 09 July 2017, 19:39

Quote:

Originally Posted by ross

Paula work every time at the same frequency (CCK).
But sample periods can be minor due to more frequent DMA 'recharge'.
It's directly related to HTOTAL: everytime H counter wrap we have two sample per channel that DMA can load
(i've semplified, the concept is that).
Smaller HTOTAL greater Paula reproduction frequency possible

Ciao,
ross

Only Paula Take advantage of it?

Toni Wilen · 09 July 2017, 20:17

Paula (or anything else) does not take any advantage of it. It is just way the system works, DMA slots have static positions at the beginning of each scan line.

The shorter the scanline, the less time it takes until next scanline and another set of DMA slots

08 July 2017, 21:12	#1
sandruzzo Registered User Join Date: Feb 2011 Location: Italy/Rome Posts: 1,894	Double Pal Question If I'm right, I've read that with doublepal dma cicles will double. Is that correct? How is possible?

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08 July 2017, 22:07	#2
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 45 Posts: 24,538	No. Double mode = scanline length is halved, number of lines is doubled. Number of DMA slots stays about the same.

09 July 2017, 20:17	#7
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 45 Posts: 24,538	Paula (or anything else) does not take any advantage of it. It is just way the system works, DMA slots have static positions at the beginning of each scan line. The shorter the scanline, the less time it takes until next scanline and another set of DMA slots

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