TT & DMA Sound

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Arne
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TT & DMA Sound

Postby Arne » Fri May 03, 2019 9:05 am

I'm playing around with STE DMA Sound for the first time i.e. creating a simple lib for playback.
If I understand DMA Sound correctly then the playback buffer has to be located in the first 4MB of ST memory.
But how can I achieve that on a TT? AFAIK DMA Sound on TTs is limited by the 4MB barrier, too.
Shall I malloc() the largest chunk of memory and the realloc() to a smaller size?
But what if the lower 4MB ST-RAM is already allocated by NVDI + buffers, AUTO folder PRGs and ACCs?
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Cyprian
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Re: TT & DMA Sound

Postby Cyprian » Fri May 03, 2019 10:24 am

Sound DMA and Shifter DMA have access to full range of ST-RAM. In case of tt it can be more that 4MB, e.g 10MB, 12MB and more?
Just reserve the memory block with Mxalloc with flag "Allocate ST-RAM only"
http://toshyp.atari.org/en/00500c.html#Mxalloc
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Re: TT & DMA Sound

Postby Arne » Fri May 03, 2019 11:37 am

If it was that easy I would not have asked. :roll:

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(Source: Atari Compendium pg.5-19)
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Re: TT & DMA Sound

Postby Cyprian » Fri May 03, 2019 12:05 pm

belive me or no,
In case of Falcon/TT there is no 4MB barrier, all DMA's - Sound, Video, ACSI/FDC (except TT SCSI DMA, which have access also to TT-RAM), have access to full ST-RAM range - max 14MB.
In case of TT/F030 use Mxalloc fore reserving ST-RAM, or just direct address ST-RAM
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Re: TT & DMA Sound

Postby mikro » Fri May 03, 2019 12:25 pm

The Compendium author hadn't realised that TT's ST RAM can be more than 2 MB.

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Re: TT & DMA Sound

Postby ThorstenOtto » Sat May 04, 2019 8:55 am

Not everything from the Compendium should be trusted literally, there have already been lots of errors discovered. But in this case, it clearly states "this limitation has been lifted on Falcon030", while Arne was talking about a STE if i understand it correctly.

Should that limitation really apply, i don't know of an easy way to ensure allocation in the first 4MB of STRAM (of course that only applies if the ST has more STRAM than that). What maybe could work is to place a small resident program in the auto folder that does the allocation via Mxalloc(STRAM ONLY), then fetch that adddress later from your application somehow.


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