Section 6.1
Some
Architectural Issues:
In
all design process ,a logical and systematic approach is essential.
This
is
particularly so in the case of the design of aVLSI
system which could otherwise take so long as to render the whole system
obsolete before it is off the drawing board.
As
example, the
case
of a relatively straightforward MSI logic circuit comprising,
say, 500 transistors.
A reasonable
time to allocate to the design and proving of such a circuit could be some two
engineer-months. Consider,
now the
design of a 500,000 transistor VLSI system.
Even if a
linear relationship exists between complexity and design time,
the required
design time would be 2000
engineer-months or 170 engineer-years.In
fact,
the design time tends to rise exponentially with increased complexity.
then we
must adopt design methods which allow the handling of complexity in reasonable periods of time
and with reasonable amount of labour.
But
now some sensible concepts applied in larger system design requirements.
Guideline
set as follows:
1.
Define the requirements (properly & carefully).
2.
Partition the overall architecture into appropriate subsystem.
3.
Consider communication paths carefully in order to develop sensible
interrelationships between subsystem.
4. Draw a floor plan of how the system is to map
onto the silicon (and alternate between 2,3 and 4 as necessary).
5.
Aim for regular structures so that design is largely a matter of replication.
6.
Draw suitable (stick or symbolic) diagrams of the leaf_cells
of the subsystems.
7.
Convert each cell to layout.
