Transcript Media:fabscalar_physical_design_final

Physical Design of FabScalar
Generated Cores
EE6052 Class Project
Wei Zhang
Outline
FabScalar Toolset
Synthesis
Physical design using IC Compiler – Problems and
solutions
Things to do next
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FabScalar Toolset
FabGen: This tool generates synthesizable RTL of a
superscalar core based on user-specified parameters:
* Frontend superscalar width
* Backend superscalar width
* Pipeline depths of canonical pipeline stages
* Issue queue size.
FabMem: This tool estimates read/write delays, read/write
energies, and area of user-specified multi-ported
RAMs/CAMs. It can also generate layouts of desired
RAMs/CAMs.
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Synthesis
FebGen-generated RTL is synthesizable.
Before starting synthesis
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Comment-out the verification components to remove
unsynthesizable verilog needed for simulation only: VPIs (the
verilog/C++ co-simulation environment) and performance counters.
Memory handling
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Use FabMem to generate custom designs of these critical memory
structures, including full layouts, SPICE netlists, and LEFs.
During synthesis, remove the behavioral modules of the memory
structures and constrain their input-port and output-port timing
paths based on timing numbers from SPICE simulation.
For place-and-route, use the LEFs to represent the memory
structures.
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Physical Design – Problems Encountered
ICC reports errors when importing netlist generated from synthesis.
Error message examples from ICC
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Error: Can not create instance master 'SRAM_4R8W' in FRAM view.
(MWDC-001)
Error: Can not create instance master 'CAM_4R4W' in FRAM view.
(MWDC-001)
Warning message examples from synthesis
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Warning: Unable to resolve reference 'SRAM_4R8W' in
'InstructionBuffer'. (LINK-5)
Warning: Unable to resolve reference 'CAM_4R4W' in 'IssueQueue'.
(LINK-5)
Cause of the errors
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No corresponding memory cells in the Milkyway library.
FabMem uses 45nm FreePDK library and our design uses the 90nm
EDK library.
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Physical Design – Problem Solutions
Solution – Adapt the memory blocks generated from the
FabMem tool to the 90nm technology.
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The FabMem tool could generate layouts of memories, from
which we can get the GDSII files.
To adapt these layouts to the 90nm technology, we need to
modify the GDSII files to
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Double the size of each physical component in the layout.
Map each layer in the FreePDK library to these layers in the 90nm
technology library.
Import these memory blocks to the Milkyway Library using
the Milkyway Environment tool and the new GDSII memory
files.
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Physical Design – Library Preparation
Before using IC Compiler, logical and physical libraries must be
created that accurately reflect the characteristics of the
available technology and cells that will be used to fabricate the
chip.
FabScalar generated cores use a lot of RAM/CAM blocks, most
of which are multi-ported.
The standard cells are already provided in the 90nm physical
library, but macros like memory blocks are not provided.
The memory blocks must be created in the physical library.
This can be done in the Milkyway Environment.
Layout data of these memory blocks are provided by FabMem.
(GDS and LEF)
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Physical Library Preparation – Memory
Layer mapping file
Generate layout of
memory blocks (using
FabMem tool)
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Extract GDSII files and
double the size of
memory blocks
Import GDSII files into
Milkyway Environment
and create CEL view
Create Milkyway library
in ICC and reference
the physical library of
memory blocks
Create FRAM view
from the CEL view and
get physical library of
memory blocks
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Library Preparation Flow in the Milkyway
Environment
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CEL View – SRAM_4R4W
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FRAM View – SRAM_4R4W
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Errors Before Adding Memory Physical
Library
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Errors After Adding Memory Physical
Library
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New Problems
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Still missing a lot of instances in the physical library
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1ICache
PreDecode_PISA_3
Decode_PISA_3
SRAM_4R8W
SRAM_4R1W
Select_3
ForwardCheck_7
The “SRAM_4R8W”and “SRAM_4R1W”could not be
generated from FabMem (only able to generate memories with
XRXW and 2XRXW ports)
Most of the other instances are very similar to memories, but
they are not standard memory blocks and could not be
generated from FabMem.
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Problems Remaining
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Still could not generate the remaining instances.
Could not move forward without these instances in the
physical library.
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