Intel IXP43X manual Electrical Interface, Topology, @33 MHz, TSU = 7 nSec

Hardware Design Guidelines—Intel®IXP43X Product Line of Network Processors

6.0PCI Interface Design Considerations

The IXP43X network processors have a single, 32-bit PCI device module that runs at 33 MHz. This chapter describes some basic guidelines to help design hardware that interfaces with PCI devices.

The PCI module is compatible with the PCI Local Bus Specification, Rev. 2.2. For a complete functional description and physical requirements, see the PCI Local Bus Specification, Rev. 2.2.

6.1Electrical Interface

The electrical definition is restricted to 3.3 V signaling environment. The device is not 5 V tolerant. All devices interfacing with the PCI module must operate at 3.3 V.

6.2Topology

Interfacing devices must be connected in a daisy-chain topology. When more than one device is in the bus, connecting stubs must be kept as short as possible.

There is a limitation to the number of devices connected to the internal arbiter. If more than four devices are required to be connected, an external arbiter is required.

The system time budget must be satisfied for 33 MHz cycles. The following equation and timing parameters must be met while routing a board that interfaces with a single PCI device or up to four devices as shown in Figure 23.

TCYC ≥ TVAL +TPROP + TSKEW + TSU

where:

TVAL = Valid Output Delay

TPROP = Bus Propagation Delay (maximum time for complete flight) TSKEW = Total Clock Skew

TSU = Input Setup Time

@33 MHz

TCYC = 30 nSec

TVAL = 11 nSec

TPROP = 10 nSec TSKEW = 2 nSec

TSU = 7 nSec

When defining the maximum length of segments A and B as shown in Figure 23, the calculation must:

•Include an additional trace length segment from the PCI connector to the input device within the expansion PCI card

•Assume the segment to be 1.5 inch

•Use trace propagation delay of 150 to 190 ps/in as specified by the PCI standard

	Intel® IXP43X Product Line of Network Processors
April 2007	HDG
Document Number: 316844; Revision: 001US	67