Page 104 - A Practical Guide from Design Planning to Manufacturing

Design Planning 79

Design Types and Design Time

How much of a previous design is reused is the biggest factor affecting
processor design time. Most processor designs borrow heavily from ear-
lier designs, and we can classify different types of projects based on
what parts of the design are new (Table 3-2).
Designs that start from scratch are called lead designs. They offer
the most potential for improved performance and added features by
allowing the design team to create a new design from the ground up. Of
course, they also carry the most risk because of the uncertainty of
creating an all-new design. It is extremely difficult to predict how long
lead designs will take to complete as well as their performance and die
size when completed. Because of these risks, lead designs are relatively
rare.
Most processor designs are compactions or variations. Compactions
take a completed design and move it to a new manufacturing process
while making few or no changes in the logic. The new process allows an
old design to be manufactured at less cost and may enable higher fre-
quencies or lower power. Variations add some significant logical features
to a design but do not change the manufacturing process. Added features
might be more cache, new instructions, or performance enhancements.
Proliferations change the manufacturing process and make significant
logical changes.
The simplest way of creating a new processor product is to repack-
age an existing design. A new package can reduce costs for the value
market or enable a processor to be used in mobile applications where it
couldn’t physically fit before. In these cases, the only design work is
revalidating the design in its new package and platform.
Intel’s Pentium 4 was a lead design that reused almost nothing from
previous generations. Its schedule was described at the 2001 Design
Automation Conference as approximately 6 months to create a design
specification, 12 months of behavioral design, 18 months of physical

TABLE 3-2 Processor Design Types
Design type Typical design time Reuse
Lead 4 years Little to no reuse
Proliferation 3 years Significant logic changes and new
manufacturing process
Compaction 2 years Little or no logic changes, but new
manufacturing process
Variation 2 years Some logic changes on same
manufacturing process
Repackage 6 months Identical die in different package