AmigaOne DMA Problem

[takemehomegrandma]

The A1 "hardware issues" derives from the MAI Articia S Northbridge. But there seems to be split opinions whether the "issues" are good or bad.

Some people thinks that it's an unknown/undocumented *feature* of the Northbridge hardware, and that it's the LinuxPPC operating system that is problematic and unstable, and that is the explanation to why the OS crashes and files gets corrupted.

Other people thinks that it's a bug in the Northbridge hardware and has either dropped development of the boards based on this chip and/or developed hardware patches (in plural) for it. The LinuxPPC operating system works fine with these patches, and even better when the Articia northbridge is completely left out of the picture in favour of another one.

Some people has also observed that even the MAI data-sheets about the Articia S no longer mentions DMA support, nor did the Article about MAI products in "IBM PowerPc News" (compare the different chips in the "Miscellaneous" row of the table, two has DMA, one has not (guess which one)). So to some people it seems obvious that not even the manufacturer themselves is prepared to sell the Articia northbridge used in the A1 as DMA capable anymore. You asked: "Hi - what is the deal with the DMA problem in the AmigaOne hardware"? The answer would be: There is none! No DMA that is! :lol:  :-P At least if you should believe the manufacturers themselves ...  

The Articia S has a lot of other issues too; it is very picky when it comes to peripheral hardware (and the way you connect them), such as memory, CD-ROM drives, etc. It also uses a kind of memory that is getting quite old, expensive, rare and hard to get. Only to mention a few things ...

[takemehomegrandma]

@ HotRod

I've read the specs for the Atricia S since some months back (allmost a year) and I haven't seen DMA mentioned for the Atricia S.

You would have to go much further back in time than that. A year ago, both the April1 and April2 patches had been released, and also the Articia based Pegasos 1 motherboard had officially been dropped altogether in favour of the DiscoveryII based Pegasos II. These issues was put forward to MAI much long before that.

Besides, I think it's rather funny that you claim that DMA is there and it's working flawlessly, when the manufacturer themselves does not even put this among the features for this particular product (they certainly do for their other (vapor since 4 years) northbridges, since DMA is a too important feature to leave out of a product description if you want to sell northbridges today). Why do they not put DMA among the features for the Articia S northbridge?

It's handled in software, not in hardware.

:-o :-o :-o

Uh, DMA in -->SOFTWARE<--?!??

The AOS 4 driver works. It is 100% reliable.

I actually have an A1 with OS4 pre-release right here, right now. Perhaps this rather unique "software implementation of DMA" would explain the "speed" in file transfers? :-D


@ Bodie

Don't know, I can't speak for PegI owners  . All I know is that I can view tv (yes, before you ask, with sound) on my A1 under Linux.

...

With reagrds to the tv cards, quite a few users (of those that I know) seem to have them working fine with their A1's. You can draw your own conclusions (and something tells me we won't agree ).

I am happy for you! :-)

Just a quick note about this; from what I understand, some TV-cards use IRQ/CPU to transfer data from the TV-card to the Graphics card, while other uses direct PCI->AGP DMA for its transfer (which completely leaves the CPU out of the picture). Some cards can perhaps even use both ways, I don't know. I am glad that your particular TV card is usable on your system! :-)

I thought the April chip fixed all the issues for the PegI

Sure, it fixes most of the issues. However, it can not "fix" things that was not implemented in the first place (like PCI->AGP DMA for instance). Anyway, the absolutely best fix against the Articia issues was the Marvell DiscoveryII (and I am SOO glad for that one)!  :lol:  :-D
 

[takemehomegrandma]

KimmoK wrote:

If you want to use Linux, most likely neither A1 or Pegasos is the best option (and especially not A1).

It depends on the application! If you want to run Linux and *real silence* is important, but without compromising too much with horse power, for instance in a media box for your living room, and real fast network speed with one (and possibly two?:-o) Gigabit Ethernet lines straight into the fast Northbridge (without going through the PCI bus) and one "traditional" 100Mbit PCI based ethernet (how is that for a home server/router/firewall for your 24/7 home network/Direct Connect efforts? ;-)  :-P ), then the Pegasos is an EXCELLENT choice! All major Linux distros runs fine, and it's only getting better all the time! :-)

[takemehomegrandma]

DrBombcrater wrote:

Actual DMA transfers on the ArticiaS work just the same as they do on any another North Bridge. The 'software' part comes when the transfer has completed. Most systems have hardware that will flag the CPU to do a partial cache-flush at ths point, in order to make sure the caches reflect the new data just DMAed into memory. The ArticiaS can't do this, so after DMA activity the driver must explicitly call an OS function that does the cache updating. This isn't exactly an elegant approach ...

This doesn't sound too healthy to me. BTW, isn't the point of DMA to keep the CPU out of the transfer process?

Anyway, perhaps both "feature+driver" and "bug+workaround" could be used to describe this (depending on your point of view I guess)! ;-)

Most TV cards are based on BT848/849 chips which do use DMA to push picture data into memory. I've seen one of these cards (a Hauppauge WinTV-Go to be exact) working on an A1 under Linux without any apparent issues.

I am in no way an expert on TV cards, but as you said, it seems like many of them are based on Brooktree/Rockwell/Connexant chipsets Bt848, Bt849, Bt878, Bt879 (at least according to the "overview" at http://www.tv-cards.com/faq.php, click on "Are all PCI TV-Cards the same?"), and at least the Bt848, Bt848A and Bt849A seems to support DMA transfer. But they should all still be able to (at least it looks that way in my ignorant eyes) fall back to IRQ/CPU transfer, righ (DMA is of course the best, but not *required*)?

"What is the minimum PC specification to use a PCI TV-Card?
 
TV-Cards based on the Brooktree/Rockwell/Connexant chipsets require the following minimum spec:

- PCI slot
- Pentium 133Mhz Processor
- DirectX Compatible sound card
- Graphics card supporting DirectDraw and Overlay
- Available IRQ

TV-Cards usually require an IRQ and a memory range but NOT an I/O address or DMA channel."

(This was from the same site (http://www.tv-cards.com/faq.php), click on "What is the minimum PC specification to use a PCI TV-Card")

How do you know that the A1 you saw was really using DMA and not falling back to using the IRQ to ask for CPU-time for it's transfer? How did you tell the difference?

BTW, "Frostwork" in this thread has a BT878 based TV card working fine in his Pegasos 1 too, so ... ;-)

Anyway, thank you for your clarifications regarding the Articia DMA. When some people talk about it, it really sounds to be a great chip! Many people seems to be really happy about it (Amiga - back for the future ;-)), and I don't want to be a party pooper here. If you people are happy about it and thinks that it's a solid ground to build an Amiga future(?) on, then I won't disturb you! But personally, I am very glad that the Pegasos moved away from it. ;-)

Have a nice day people! :-)

[takemehomegrandma]

smithy wrote:

I actually have an A1 with OS4 pre-release right here, right now. Perhaps this rather unique "software implementation of DMA" would explain the "speed" in file transfers?

How about writing a review, comparing MOS and OS4? :-)

Hmm, that sounds like a plan, doesn't it? ;-)