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Old 08 July 2017, 21:12   #1
sandruzzo
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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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Old 08 July 2017, 22:07   #2
Toni Wilen
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No.

Double mode = scanline length is halved, number of lines is doubled. Number of DMA slots stays about the same.
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Old 08 July 2017, 22:13   #3
ross
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Quote:
Originally Posted by sandruzzo View Post
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

Last edited by ross; 08 July 2017 at 22:23. Reason: []
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Old 09 July 2017, 17:03   #4
sandruzzo
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Quote:
Originally Posted by ross View Post
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
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Old 09 July 2017, 18:23   #5
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Quote:
Originally Posted by sandruzzo View Post
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
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Old 09 July 2017, 19:39   #6
sandruzzo
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Quote:
Originally Posted by ross View Post
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?
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Old 09 July 2017, 20:17   #7
Toni Wilen
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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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