Intel 820E 3.2. AGTL+ Design Guidelines

Intel® 820E Chipset
R
Design Guide 141
Term Definition
Simultaneous
switching
output (SSO)
effects
Difference in electrical timing parameters and degradation in signal quality caused
by multiple signal outputs simultaneously switching voltage levels (e.g., high to
low), in the direction opposite to a single signal (e.g., low to high) or in the same
direction (e.g., high to low). These are respectively called odd-mode switching and
even-mode switching. This simultaneous switching of multiple outputs creates
higher current swings that may cause additional propagation delay (or “push-out”)
or a decrease in propagation delay (or “pull-in”). These SSO effects may affect the
setup and/or hold times and are not always taken into account by simulations.
System timing budgets should include margin for SSO effects.
Stub Branch from the trunk terminating at the pad of an agent
Test load Intel uses a 50 Ω test load for specifying its components.
Trunk The main connection, excluding interconnect branc hes, terminating at agent pads
Undershoot Maximum voltage a signal may extend below VSS at the processor core pad. See the
respective processor’s datasheet for the undershoot specifications.
Victim A network that receives a coupled crosstalk signal from another network is called
the victim network.
VREF guard
band
A guard band (∆VREF) defined above and below VREF, to provide a more realistic
model accounting for noise, such as crosstalk, VTT noise, and VREF noise
3.2. AGTL+ Design Guidelines
The following step-by-step guideline was developed for systems based on two processor loads and one
Intel 82820 MCH load. Systems using custom chipsets will require timing analysis and analog
simulations specific to those components.
The guideline recommended in this section is based on experience accumulated at Intel while developing
many different systems based on the Intel® Pentium® Pro processor family and the Pentium III processor.
First, perform an initial timing analysis and topology definition. Then perform pre-layout analog
simulations, for a detailed picture of a working “solution space” for the design. These pre-layout
simulations help define the routing rules prior to placement and routing. After routing, extract the
interconnect database and perform post-layout simulations to refine the timing and signal integrity
analysis. Validate the analog simulations when actual systems become available. The validation section
describes a method for determining the flight time in the actual system.
Guideline Methodology
• Initial timing analysis
• Determine general topology, layout, and routing.
• Pre-layout simulation
 Sensitivity sweep
 Monte Carlo Analysis
• Place and route board
 Estimate component-to-component spacing for AGTL+ signals.
 Lay out and route board.
• Post-layout simulation
 Interconnect extraction
 Intersymbol interference (ISI), crosstalk, and Monte Carlo Analysis
• Validation
 Measurements
 Determining flight time