OL2.FEB–Digital Equipment Corp.–RM
Digital goes for PCI bus with a bridge chip and chipsets
Digital Equipment Corp.is sampling the 21050 PCI bridge chip, a part that could make Peripheral Component Interconnect (PCI) a total I/O solution on servers and high-end desktops. At the same time, Digital announced two system-logic chipsets that will run with any Alpha 21064 microprocessor up to 275 MHz.
The PCI bridge
Far more than just a buffer, the 21050 bridge provides a panoply of important services to traffic between two 32-bit buses. These services allow hierarchical bus trees with up to 32 PCI slots on a system (see diagram).
They also allow peripheral boards to be made with up to four functions. An example is a quad ethernet board, on which a 21050 interfaces the card edge on one port, and a secondary PCI bus on the board joining four ethernet controllers.
Both buses run at 33 MHz and comply with PCI Revision 2.0. For memory transactions, the chip:
* Conditionally forwards reads and writes upstream and down.
* Filters memory transactions through two address regions, one prefetchable, one not.
* Provides read prefetching in the permitted region.
* Buffers up to 32 bytes of write posting.
For I/O operations, the chip:
* Conditionally forwards reads and writes upstream and down.
* Provides ISA awareness
* Provides transaction filtering through one programmable memory I/O address range.
The 21050 transmits configuration reads or writes downstream, and configuration writes to special cycles either way.
Other general services of the bridge chip are:
* Concurrent resource lock.
* Lock propagation across the bridge.
* Master latency and target wait timers that limit latency on either bus.
* Dual-address transaction forwarding upstream.
* Programmable rotating arbitration of up to six bus masters on the secondary bus.
* Bus parking on the secondary side.
* Error checking on both sides.
For video, the 21050 supports forwarding of VGA memory and I/O addresses, and snooping of VGA palette I/O writes.
Motherboard sets
Digital's two new chipsets are the 21071 and 21072. The 21071 chipset includes a memory controller, a PCI interface, and two data path chips. At $90, it is more expensive than many Pentium chipsets, but it can run with 21064s up to 275 MHz. It offers a 64-bit memory path. By easing entry for PC makers, it may overcome their current reluctance to dive in with Alpha.
For higher-end machines, the six-chip 21072 set features a 128-bit memory path with error correction. This should provide all the performance available from a uniprocessor 21064 server.
An evaluation board, EB64+, comes with an example motherboard design with supporting example files, source code, and simulation database. It serves as a trial system for benchmarking and debugging software.
The 21050 bridge chip costs $22.80 each per 5,000 in 208-pin plastic quad flatpacks. The 21071 motherboard chipset is $90 each in lots of 5,000. The 21072 set is $140 each per 5,000. Samples are available now, production quantities are expected in the second quarter. The EB64+ evaluation board is available now for $5,000. For more, call DECchip Information at 800-DEC-2717 or .
–Rodney Myrvaagnes
CAPTION FOR DIAGRAM:
The 21050 PCI bridge expands both the electrical and logical capacity of the PCI bus, making system boards with up to 32 PCI slots possible.
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