Techie questions regarding the new Amiga OS4 update

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Spirantho

Re: Techie questions regarding the nuw Amiga OS4 update

Posted on: 2007/8/13 18:04 #21

Quite a regular

@Hans

Quote:

Hans wrote:
@Spirantho

So large allocvec allocations might be fragmented physically in memory? I didn't realize that; although it's only important when you're writing a driver.

I think so. Certainly I know that if you do a StartDMA() on anything larger than a few KB then StartDMA() fails.

In the old SDK you could use AllocMem() with a "contiguous" tag, and then StartDMA would succeed on large blocks, but since AllocMem was deprecated in favour of AllocVecTags you can't do that any more and you can't ever do a StartDMA unless you happen to be dealing in a small enough chunk.

--
Ian Gledhill
ian.gledhill@btinternit.com (except it should be internEt of course...!)
Check out my company's shop: http://www.mutant-caterpillar.co.uk/shop/ - specialising in Sinclair Spectrums but will be adding Amigas!

Rogue

Re: Techie questions regarding the nuw Amiga OS4 update

Posted on: 2007/8/13 18:50 #22

Quite a regular

@Spirantho

Quote:

Spirantho wrote:

It means that absolutely no way anyone outside of the people with the Beta SDK can allocate a contiguous chunk of memory - which isn't good for device drivers like I'm writing!

Yeah, I'm aware of that, OTOH there aren't that many driver writers. Like I said I need to see what I can do.

Seriously, if you do want to contact me write me a mail. You're more likely to get a reply then.

Rogue

Re: Techie questions regarding the nuw Amiga OS4 update

Posted on: 2007/8/13 18:53 #23

Quite a regular

@Hans

Quote:

Hans wrote:

So large allocvec allocations might be fragmented physically in memory? I didn't realize that; although it's only important when you're writing a driver.

Fragmentation only affects physical addresses. The CPU will not see anything of that nature on user code, i.e. you will be able to access memory normally. But yes, as a matter of fact any allocation might (and very likely will) be scattered, anything beyond 4k which is the current page size.

For just about anybody, this will not have any consequence. This is ONLY interesting for memory that is used in a DMA operation. Even there, though, you don't need to have contiguous memory if you use StartDMA which makes a scatter/gather list for you. It of course assumes that the DMA operation in question supports Scatter/Gather.

Seriously, if you do want to contact me write me a mail. You're more likely to get a reply then.

bean

Re: Techie questions regarding the nuw Amiga OS4 update

Posted on: 2007/8/13 19:33 #24

Not too shy to talk

@Rogue

Quote:

I'll see what can be done about this, but a new SDK is currently not very likely to be released.

Ouch! That is a shame.

OS4.1 + an A1XE with an appetite for batteries!

Hans

Re: Techie questions regarding the nuw Amiga OS4 update

Posted on: 2007/8/13 20:00 #25

Home away from home

@Rogue

Quote:

Rogue wrote:
@Hans
For just about anybody, this will not have any consequence. This is ONLY interesting for memory that is used in a DMA operation. Even there, though, you don't need to have contiguous memory if you use StartDMA which makes a scatter/gather list for you. It of course assumes that the DMA operation in question supports Scatter/Gather.

The Bt878 (and the newer derivative Spirantho's got) support writing each row in the image to different locations. So he could probably use AllocVec() with MEMF_PUBLIC set and StartDMA()/GetDMAList() for now.

I'm interested in this stuff for future reference really. I'm not working on writing drivers right now; but I might do so later.

Hans

Chris

Re: Techie questions regarding the nuw Amiga OS4 update

Posted on: 2007/8/17 22:26 #26

Amigans Defender

@bean

Agreed, although I managed to get the info I needed from another source. There are still things added since the previous public SDK that I would like to know about, however.

Chris

corto

Re: Techie questions regarding the nuw Amiga OS4 update

Posted on: 2007/8/18 11:54 #27

Not too shy to talk

Quote:

Rogue wrote:
@Spirantho

Yeah, I'm aware of that, OTOH there aren't that many driver writers. Like I said I need to see what I can do.

If I had a driver to develop I don't know which would be the first step and where to find information. It would be nice to give more about driver writing under OS4 in the next SDK.

Why not an example for a simple PCI card ?

That's nice to read technical info here and ideas for the future !

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