PDA

View Full Version : PCI Slot-to-slot transfers



despaxas
05-25-2001, 04:23 AM
I was reading the manual to an old video capture card (Bravado 1000), and it warned of capturing to drives connected to SCSI cards because it "does not support slot-to-slot transfers". Wouldn't all data have to travel through the Bandit controller to be directed to another slot? Maybe they don't mean directly from slot-to-slot. Has anyone ever heard of this? Is this something that just effects older cards? I've never heard of this being a problem.

dragon_x
05-25-2001, 09:02 AM
I think most PCI cards are like this - that is that they want to talk to the main bus and/or CPU. I think the S900 had some 'feature' that allows direct slot to slot communication (for the cards that support this). Generally SCSI cards want to be in the BUS MASTER slot .

Not sure what Mac you would put this in or what kind of setup you have, but I would bet a modern controller (MilesU2W) and modern SCSI drives (10K Cheetah or faster) would work fine. I would guess the only possibe issue would be a bus master issue. If you only have one bandit/PCI controller and the SCSI and Bravado are fighting each other for controll... the computer can become unstable.

Of course this is a wild *ssed guess http://macgurus.com/infopop/emoticons/icon_smile.gif

You might want to check out the FUSE or IGNITER manual - to see how a new board compares. I think I recall people saying that the FUSE works best in newer Macs (beigeG3). Its fine in oldermacs, but you dont get the throughput of the newer systems.... (or was that an S900 issue?).

trag
05-25-2001, 12:24 PM
In theory, PCI devices can write directly to each other without involving the Bandit controller. The Bandit controller isn't, strictly speaking, a controller. It is a Bridge. It exists on both the PCI bus and on the CPU bus (CPU bus is where RAM, CPU and one side of the Bandits live). It translates PCI transactions to CPU transactions and vice versa.

Bus Mastering means the ability to take control of the PCI bus. There is a set of commands used on the PCI bus to read and write to various addresses. Each PCI card occupies some set of addresses. So a card which has gained control of the PCI bus, could write or read data directly to the addresses of another PCI card without involving the Bandit.

From the perspective of the chip which arbitrates the PCI bus, the Bandit is just another device on the bus, like any card. Arbitrating the PCI bus means deciding who is the Bus Master at any given moment. All of the slots in a Macintosh are capable of Mastering the Bus. There is no single Bus Mastering slot, though the upper slots seem to offer a performance advantage for some reason.

In most instances a PCI card writes or reads to addresses that represent system memory. Because system memory is RAM and is over on the CPU bus, these transactions go to the Bandit. In other words, addresses that represent system memory are assigned to the Bandit on the PCI bus, so those transactions are targeted at the Bandit.

despaxas
05-26-2001, 08:11 PM
perfect...that's exactly what I needed to know. Thank you! http://macgurus.com/infopop/emoticons/icon_smile.gif