Cache design

1. EN160: VLSI Project
Spring 2008
Cache Memory Simulation
By: Holiano, Chaka, and Rotor

2. Index Title Page no.
0.0 Tables of Contents 1
1.0 System Overview 2
1.1 -System Diagram 2
1.2 -Specifications 2
1.3 -I/O List 3
1.4 -Direct-mapped Cache Algorithm 3
1.5 -Main Components Description 4
2.0 Components Descriptions
2.1 -Memory Cell 5
2.2 -Memory Cell Tests and Timing 6
2.3 -Demux 1-to-4 7
2.4 -Mux 4-to-1 7
2.5 -Demux 1-to-4 Tests 8
2.6 -Mux 1-to-4 Tests 9
2.7 -4-bit Tag Comparator 10
2.8 -4-bit Tag Comparator Tests 10
3.0 Final System
3.0 -Core Layout 11
3.1 -Core + Pads + Test Signal Layout 11
3.2 -Core Placement and Layout 12
3.3 -SPR Setup 12
3.4 -PADFrame Placement and Layout 13
3.5 -Placement and Routing Summary 13
3.6 -DRC Error Check 14
3.7 -DRE Geometry Error Details (disabled check) 15
4.0 Systems Testing
4.1 -Read/Write Test 16
4.2 -Hit/Miss Test 17
4.3 -Hit/Miss Timing Analysis 17
5.0 Conclusion 18
6.0 Pin Layout 19
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3. System Diagram:
Tag_In Line_In Data_In
4bits 2bit 8bit We
Tag Line Data F2
Tag Data
Re
Demux
4 bits
Tag Data
4 bits
Tag Data
Tag Data
Comparator
Demux
4 bits
F1
32 bits
4 bits
Mux
2 bits
8 bits
Status Data_Out
Specification:
Data width: 8-bit
Tag: 4-bit
Address: 4-bit
Index 2-bit
Replacement Policy: Direct Mapped Cache Fill
Perform the following functions:
Operation Read_en Write_en Status Data Out
Read-Hit 1 X 1 Mem[index]
Read-Miss 1 X 0 Previous Data
Write-Hit 0 1 X X
Write-Miss 0 1 X X
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4. Inputs:
From CPU:
New Data: 8-bit
Address: 6-bit
Address<5:2> Tag: 4-bit
Address<1:0> Index: 2-bit
Read enable: 1-bit
Write enable: 1-bit
Outputs:
To CPU:
Dataout: 8-bit
Status: 1-bit [Signifies when data is ready]
Total pins required: 25pins + 1 Vdd + 1 gnd.
Extra outputs:
Ring Oscillator Test Signal: 1-bit
Ring Oscillator Test Signal w/En: 2-bits
Inverter: 2-bits
Replacement Algorithm: Direct Mapped Cache Fill
This is the fastest algorithm for cache replacement where the cache takes 2 least significant bits of the
address as index. It essentially takes the main memory address and indexes the address by using
modulus.
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5. Main components:
Muxes/Demuxes – The memory design simulates a cache memory, similar to a register memory. Muxes
are essential in ensuring that data from the memory cells can be selected for the output. The demuxes is
essential in ensuring that the signals between the components arrive at the correct memory cell for
proper operation.
Memory – Stores all the cache memory data, read or write only. In the design, read is prominent, you
cannot write while read is on, but you can read while write is on. The memory cells are designed using
flip-flops, and modified to have two signals for read and write enables. In each memory line/cell we
store 8-bits of actual data, and 4-bit for tag comparison.
Comparator – Compares the Tag of the data from the memory, and the Tag of the data requested.
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6. Memory Cell:
1-bit Cell:
This is a single bit memory cell utilizing the Flip-flop design and a independent read or write enable
signals. Q is the output of the memory cell, and Q_b is the inverted output.
12-bit Memory Cell:
Cascaded single-bit cells to form one line. We have separate read and write signals for tag and for the
data.
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7. Read/Write Test:
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8. 1-bit Demux 1-to-4
1-bit Mux 4-to-1
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9. Demux 1-to-4 Test:
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10. Mux 4-to-1 Test:
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11. 4-bit Tag Comparator:
Comparator Test:
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12. Core Layout:
Core + Pads + Test Signals Layout:
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13. Core Placement and Layout:
Core = 2448λ x 1232.5λ
SPR Setup:
3-metal Layers:
H2: Metal3
V-H2: Via2
V: Metal2
H1-V: Via1
H1: Metal1
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14. PadFrame Placement and Layout:
Placement and Routing Summary:
SPR SUMMARY 'mAMIs050DL_AND_PADS.tdb'
Date and time : 05/22/2008-21:12
1 Lambda = 1.000 Lambda = 3.333 Micron(s)
Design file : E:reda en160 proj BUmAMIs050DL_AND_PADS.tdb
Netlist file : Projectcache_pads.tpr
Library file : mAMIs050DL_AND_PADS.tdb
Placement optimization factor : 1.00
Routing optimization (3 layer) : Netlength and via reduction
Standard Cell Place and Route done :
- Core cell "Core" generated.
- Padframe cell "Min_Frame" generated.
- Chip cell "Library_Test_s" generated.
-------------------------------------------------------------
Number of standard cells : 184
Number of signals in netlist : 336
Core size in Lambda : 2438.5 x 1128.5
Core area (Lambda^2) : 2751847.25
Frame size in Lambda : 5000.00 x 5000.00
Frame area (Lambda^2) : 25000000.00
Length of nets in core : 161951.00 Lambda
Generated vias in core : 647
SPR elapsed time : 0:00:04
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15. DRC Error Check:
L-Edit DRC SUMMARY REPORT
EXECUTION SUMMARY
Execution Start Time May 22 2008 21:20:11
L-Edit Version L-Edit Win32 12.10.20060718.19:30:32
Rule Set Name MOSIS AMI 0.50UM - SUBMICRON RULES_ Last Updated 10/08/2001
File Name E:reda en160 proj BUmAMIs050DL_AND_PADS.tdb
Cell Name Channel_4 (May 22 21:20:08 2008)
User Name Rotor
Computer Name SREDA-XP1
Memory used at start 46.5M
DRC JOB RESULTS SUMMARY
Total DRC Errors Generated 0
CPU Time 00:00:05
Real Time 00:00:05
Rules Executed 93
DRC Errors Generated by Rule Set
DRC Standard Rule Set 0
RUN-TIME DRC ERRORS AND WARNINGS
GEOMETRY FLAG SUMMARY
ACUTE ANGLES Disabled
ALL ANGLE EDGES 0
OFFGRID Disabled
ZERO-WIDTH WIRES 0
POLYGONS WITH OVER 199 VERTICES 0
WIRES WITH OVER 200 VERTICES 0
SELF INTERSECTIONS 0
WIRE JOIN/END STYLES 0
CELLS WITH ERRORS FOUND
RESULTS SUMMARY
DRC Errors Generated 0
CPU Time 00:00:05
REAL Time 00:00:05
Input Objects 404 (404)
Rules Executed 93
Geometry Flags Executed 6
Disabled Rules 18
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16. DRC Geometry Error Details (Acute Angles):
Error #1
Error #6
These error checks were disabled.
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17. Systems Analysis:
Single-bit Read/Write Systems Test:
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18. Status Hit/Miss Systems Test:
Timing Analysis:
Read time:
 tdf = 17ns
 tdr = 9ns
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19. Conclusion:
We successfully implemented a Cache Memory Simulation device. All verification data appears to meet
the design criteria. There were unpredictable design errors on the way, but none that stopped the cache
memory to function normally. DRC errors turned up geometrical errors on the Padless frame generated
by SPR. The DRC errors also determined that there were some metal to metal spacing errors in the core
after SPR. There were also disconnected Metal layers on the Padless Frame that had to be manually
connected.
We have not yet expanded the design to include fetching control systems to a Main Memory system.
This is a functionality that can be added on in the future. We also have not expanded the cache size, to
determine the maximum size of cache that is possible using the type of memory cells that we have.
Other improvements would be to actually use 6T SRAM cell design for the memory cell instead of Flip-
flops that requires more area due to more transistors in each memory cell.
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20. Pin Layout:
Index<0>
Index<1>
Test2_in
Test1_in
Tag<0>
Tag<1>
Tag<2>
Tag<3>
We
Re
Data<7> Test1_out
Data<6> Data_out<0>
Data<5> Data_out <1>
Data<4> Data_out <2>
Vd-d Data_out <3>
Data<3> gnd
Data<2> Data_out <4>
Data<1> Data_out <5>
Data<0> Data_out <6>
Test3_out Data_out <7>
Status
Data_out_sl<7>
Data_out_sl<6>
Data_out_sl<5>
Data_out_sl<4>
Data_out_sl<3>
Data_out_sl<2>
Data_out_sl<1>
Test2_out
Data_out_sl<0>
Test Signals:
Test 1: Test1_in Test1_out Test2: Test2_in Test2_out Test 3: Test3_out
Inverter 0 1 Ring 0 0 Ring
Oscillator Oscillator
1 0 w/En 1
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