Crossfire Platform and Integration
As also mentioned in our tech preview, Crossfire is a platform much like NVIDIA SLI is. That means a combination of supporting core logic on a specific mainboard and Crossfire-supporting graphics cards, both master and slave.Crossfire-supporting core logic and mainboards
Crossfire technically doesn't need anything more than a mainboard that has a pair of PCI Express 16X physical slots connected to core logic that supplies two of what's called a PCI Express root port. Connect the two cards to the root ports via the physical slots and they can communicate with each other to provide the channel for passing data that's needed for some of Crossfire's features to work. That's it. So Crossfire can technically work with ATI core logic like RS480 and RX480, NVIDIA nForce4, VIA K8T890 Pro, a couple of SiS chipsets and a wide range of Intel chipsets from i915 upwards.The reality is that - like NVIDIA and SLI being locked to nForce4 SLI and Intel E7525 - ATI are, initially at least, locking it down to their own PCI Express core logic (and specifically certain variants of those) and Intel i955X. ATI's own Crossfire Edition core logic comes in AMD Athlon 64 and Intel Pentium 4-supporting flavours and while the AMD variant is to be picked up by a majority of mainboard vendors due to the size of that market, the Intel side of things is most likely to be supported by marked Intel i955X mainboards.
The AMD reference platform is called Halibut, created by the ATI mainboard team in Canada and supported by the ASIC design team headed by John Bruno. John and his guys work with the mainboard team to create a reference design that the board vendors can implement for their own full production designs.
So, at least initially, you need a Crossfire Edition mainboard that's explicitly marked as such that has ATI or Intel i955X core logic. Moving forward, ATI are likely to start engineering in Crossfire-specific enhancements to their core logic that will include, but isn't limited to, passing data from the slave to the master across the bus to raise performance of Super AA mode. More on that later.
Crossfire Edition graphics card
As you'll know by now, Crossfire will also require the use of a Crossfire Edition graphics card. The Crossfire Edition graphics card contains the input and output hardware required for accepting image date from the slave and outputting it to your analogue or digital display. That's the case for Radeon X8-series Crossfire and also the upcoming X1x-series.Integration of the two
Integrating Crossfire into a system isn't as simple as integrating SLI but it's also no more involved. With a Crossfire Edition mainboard in your chassis, you need to make sure you insert the Crossfire Edition and the slave graphics board into the right slots. On Halibut reference designs the master board goes in the bottom PEG16X slot and the slave goes into the top slot, counter to what you'd logically assume. Getting that wrong with Halibut gets you a system that POSTs and will boot all the way into your OS but you can't actually see it do so since the displays aren't initialised correctly.Halibut reference BIOS revisions also require you toggle the Dual Display option for Crossfire to work correctly. In terms of mapping the PCI Express lanes to the right slots, the Halibut mainboard is 8/8 by default and you have a rerouting card to place in the slave slot if you want 16 lanes to the master slot. It works much like the initial switching cards seen with SLI.
Cabling between the master and slave is done with a three-ended cable. You connect the DVI output from the slave to the high-density connector on the Crossfire Edition master board, leaving a female DVI output left for connecting a display. The cable can't be connected in any way other than the correct one due to pin count and connector orientation, so no need to worry about that. Except when your slave has dual DVI outputs, in which case it needs to be the output connected to the primary TMDS. Consult your slave board manual for the correct output.
Then you need to install the Crossfire Edition mainboard software followed by the Crossfire display driver. CATALYST 5.10 is likely to be the first official release of a Crossfire display driver from ATI, with the CATALYST 5.9 BETA software used currently not likely to see the official WHQL stamp before 5.10 is ready to go. Differences between the two might well be fairly large, more on which later.
You can integrate Crossfire with both boards present and cabled up before any display driver is installed, or you can do slave first and master later, or master first and slave later. Put simply, adding either master or slave boards to a system that doesn't contain one or the other is fine.
Displays available after integration
After integration of Crossfire, your display connectivity options are numerous. With four outputs available from Crossfire Edition and slave boards, you lose all outputs from everything but the main Crossfire display in Crossfire mode. The other display outputs are only active with Crossfire switched off, much like current SLI. When that's the case, you have three possible outputs with Crossfire connecting cable in place, four otherwise. The Crossfire cable obviously joins the output from the slave to the input into the master with one display output from that, resulting in one display from two connectors used.Then you've got another DVI display from the Crossfire Edition master and the other display connector on the slave, usually an analogue output. So three or four possible displays depending on whether you've got the cable connected and obviously Crossfire only works when that's the case.
If there's a display output present on the Crossfire Edition mainboard on ATI-based Crossfire Edition mainboards (not Intel i955X), due to the use of RS480 (AMD, with RX480 the version without integrated graphics) or RD400 (Intel), that output is also available if Crossfire is turned off, regardless of cable connected. Confused? Don't be.
The rule is thus: count the female display connectors you've got available, cable or no cable, and they'll all be available if Crossfire is switched off. If Crossfire is on, which needs the cable, only the display on the end of the cable will be active.
Want to see boards in picture so you can visualise it, rather than imagine it all by wading through this text? Thought you'd never ask.
