The upcoming PPC controllers have one thing in common ...

Tundra TSI110: 2 x4 PCI-Express
Freescale MPC8641(D): 2 x8 PCI Express
Marvell Discovery V: PCI-Express (but unknown in what format?)

... that is, PCI Express!

I was reading up a little on this subject. Wikipedia has a good summary IMHO, and this quote was quite informative:

pci_express_001.PNG

"A connection between any two PCIe devices is known as a "link", and is built up from a collection of 1 or more lanes. All devices must minimally support single-lane (x1) links. Devices may optionally support wider links composed of 2, 4, 8, 12, 16, or 32 lanes. This allows for very good compatibility in two ways. A PCIe card will physically fit (and work correctly) in any slot that is at least as large as it is (e.g. an x1 card will work in an x4 or x16 slot), and a slot of a large physical size (e.g. x16) can be wired electrically with fewer lanes (e.g. x1 or x8; however it must still provide the power and ground connections required by the larger physical slot size). In both cases, the PCIe link will negotiate the highest mutually supported number of lanes."

This sounds very flexible IMO. But just for the sake of over-clarifying things for my thick brain - if the controller specifications say 2 x4, or 2 x8, can those be:

1) *Split up* into, say, several x1 lane links that is wired electronically to *a couple* of slots?

2) *Joined* into x8 (for the Tundra) or x16 (for the 8641) that is wired to a single physical slot?

Sorry for this stupid question ...

Are those toasters?

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Hehe, yeah, it's the Toastmaster Deluxe series, ranging all the way up to the military grade x16 industrial toaster for the really hungry ones!

I wonder how many mega-bites/second that can be made with the x16 device.

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x16 device will chew in one piece

>This sounds very flexible IMO. But just for the sake of over-clarifying things for my thick brain
>- if the controller specifications say 2 x4, or 2 x8, can those be:

>1) *Split up* into, say, several x1 lane links that is wired electronically to *a couple* of slots?

This depends on the implementation of the controller.
If there are no details given I would say no!
E.g. Freescale recommends a PCIe switch chip if you need partitioning of one of the x8 links in MPC8641.

>2) *Joined* into x8 (for the Tundra) or x16 (for the 8641) that is wired to a single physical slot?

Now this also depends on the implementation. If there is not additional info given I would per default rather assume that it is not the case.

There ARE chips that can do it, such as the RM11200.

The special problem with the MPC8641D is that the system interface of the OCeaN switch to which PCIe/RapidIO and a DMA controller are connected does not provide more than 2.7GB/s of fullduplex bandwidth to the rest of the system (and memory).
This is sufficient for 2GB/s PCIe x8 but not 4GB/s x16, so you would have a phantom feature here.

If someone missed the Tundra announcement:
http://www.ppcnux.com/modules.php?name=News&file=article&sid=6087

[ Edited by tarbos on 2006/1/17 20:42 ]

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Thanks for the info!

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Darn bottlenecks ...

Wiring the first x8 to a x16 slot for graphic card purpose would still be a good idea, wouldn't it?

The second channel could perhaps be split, to be able to connect a few more cards of other types?

What other types of cards are there now (except graphic cards)? I suspect there are high performance RAID controllers, but any other? What are the typical physical size of these slots? I mean, is there a point at all in putting a x1 or x4 slot on the motherboard, or should you go for x8 and x16 only?

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That article was an excellent compilation of information (as usual on the PPCNux site)!

>Wiring the first x8 to a x16 slot for graphic card purpose would still be a good idea, wouldn't it?

Great idea!

>The second channel could perhaps be split, to be able to connect a few more cards of other types?

Either that and/or connect a southbridge to it.
Here you have the choice among ULi M1575/1573 or ATI's SB460/450 and the upcoming SB600
that makes it a complete desktop system and offer an additional PCI bus for legacy expansion cards.
Even the SIS southbridge in the Xbox360 uses a PCIe interface to connect to the integrated ATI
system controller/gfxchip.

>I mean, is there a point at all in putting a x1 or x4 slot on the motherboard,

Yes, space considerations.
E.g. 64Bit PCI-X slots would not fit very well on the very small Pegasos board.

>or should you go for x8 and x16 only?

Apple did go that route, as you can see in the system topology.
On the other hand, 16x PEG slots are defined for 75W power while the smaller ones require only 25W,
so you have to make sure you can supply what the cards expect.
This may be one of the reasons the PowerMac PSU is a 1000+ Watt monster.