Re: AU/HAL buffer alignment
Re: AU/HAL buffer alignment
- Subject: Re: AU/HAL buffer alignment
- From: Kurt Bigler <email@hidden>
- Date: Mon, 10 Mar 2003 13:11:13 -0800
on 3/10/03 12:11 PM, Jeff Moore <email@hidden> wrote:
>
The HAL doesn't make any guarantees about the alignment of the buffers.
>
I don't think that Audio Units make any guarantees about the alignment
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of the buffers either.
>
>
The HAL uses malloc to allocate it's buffers. The default behavior of
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malloc is to allocate chunks a page or larger in size so as to be page
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aligned. Chunks smaller than a page don't have any guarantees about
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alignment.
Thanks. And I have to admit I don't know for sure how big a page is - 4K?
I just did some ADC searches related to page size, alignment, and malloc,
but didn't turn up anything relevant about page size or about malloc
behavior.
A guess: maybe malloc does page alignment on larger objects it still does
128-bit alignment on smaller ones?
It has been my impression based on CodeWarrior experience (including some
release notes a year or more back) that all heap allocation methods are now
128-bit alignment safe. Maybe this is specific to CWs own run-time support,
but would expect CW to follow Apple's lead on this kind of thing.
So I would have figured that if the HAL allocated _each_ buffer directly
using malloc that this would be good news.
Do you have a pointer to better doc on malloc? Or should I look in Darwin?
I suppose I could just write all my altivec code to not depend on alignment,
but I suspect that might make for a bit more work.
Thanks for your help,
Kurt Bigler
>
>
On Saturday, March 8, 2003, at 11:05 PM, Kurt Bigler wrote:
>
>
> All the buffers passed by an output AU to my render callback appear to
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> be VERY aligned - like on a 4K boundary. Is this something we can
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> count on for buffers passed from both output AUs and the HAL?
>
>
>
> The real question is whether we can count on 128-bit alignment, to
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> simplify AltiVec development.
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>
>
> Thanks,
>
> Kurt Bigler
>
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