1. FPGA Devices & FPGA Design Flow
ECE 545
Lecture 2
FPGA Devices & FPGA Design Flow

2. Two competing implementation approaches
FPGA
Field Programmable
Gate Array
ASIC
Application Specific
Integrated Circuit
designed all the way
from behavioral description
to physical layout
no physical layout design;
design ends with
a bitstream used
to configure a device
designs must be sent
for expensive and time
consuming fabrication
in semiconductor foundry
bought off the shelf
and reconfigured by
designers themselves

3. What is an FPGA? Configurable Logic Blocks I/O Blocks Block RAMs

4. Which Way to Go? ASICs FPGAs Off-the-shelf High performance
Low development cost
Low power
Short time to market
Low cost in
high volumes
Reconfigurability

5. Other FPGA Advantages
Manufacturing cycle for ASIC is very costly, lengthy and engages lots of manpower
Mistakes not detected at design time have large impact on development time and cost
FPGAs are perfect for rapid prototyping of digital circuits
Easy upgrades like in case of software
Unique applications
reconfigurable computing

6. Major FPGA Vendors SRAM-based FPGAs Xilinx, Inc. Altera Corp. Atmel
Lattice Semiconductor
Flash & antifuse FPGAs
Actel Corp.
Quick Logic Corp.
Share about 90% of the market

7. The Programmable Marketplace Q1 Calendar Year 2005
PLD Segment
FPGA Sub-Segment
Lattice
QuickLogic: 2%
Xilinx
Actel
Other: 2% 5% 7%
58%
33%
51%
31%
11%
It is clear from these two charts that Xilinx is not only the clear leader in programmable logic products, but is also the leader in FPGA market share. This is due primarily to the fact that we produce products the meet the requirements of our customers. We understand the problems facing our customers and we make it our business to provide solutions to those problems
Note: Atmel and Cypress number (each less than 1%) are not included in this calculation.
Xilinx
Altera
Altera
All Others
Two dominant suppliers, indicating a maturing market
Source: Company reports
Latest information available; computed on a 4-quarter rolling basis

8. ISE Alliance and Foundation Series Design Software
Xilinx
Primary products: FPGAs and the associated CAD software
Main headquarters in San Jose, CA
Fabless* Semiconductor and Software Company
UMC (Taiwan) {*Xilinx acquired an equity stake in UMC in 1996}
Seiko Epson (Japan)
TSMC (Taiwan)
Samsung (Korea)
Programmable
Logic Devices
ISE Alliance and Foundation
Series Design Software

9. Xilinx FPGA Families Old families XC3000, XC4000, XC5200
Old 0.5µm, 0.35µm and 0.25µm technology. Not recommended for modern designs.
High-performance families
Virtex (220 nm)
Virtex-E, Virtex-EM (180 nm)
Virtex-II (130 nm)
Virtex-II PRO (130 nm)
Virtex-4 (90 nm)
Virtex-5 (65 nm)
Virtex-6 (40 nm)
Low Cost Family
Spartan/XL – derived from XC4000
Spartan-II – derived from Virtex
Spartan-IIE – derived from Virtex-E
Spartan-3 (90 nm)
Spartan-3E (90 nm) – logic optimized
Spartan-3A (90 nm) – I/O optimized
Spartan-3AN (90 nm) – non-volatile,
Spartan-3A DSP (90 nm) – DSP optimized
Spartan-6 (45 nm)

11. CLB Structure

12. General structure of an FPGA
The Design Warrior’s Guide to FPGAs Devices, Tools, and Flows. ISBN Copyright © 2004 Mentor Graphics Corp. (

13. Xilinx CLB
The Design Warrior’s Guide to FPGAs Devices, Tools, and Flows. ISBN Copyright © 2004 Mentor Graphics Corp. (

14. CLB Structure
The configurable logic block (CLB) contains two slices. Each slice contains two 4-input look-up tables (LUT), carry & control logic and two registers. There are two 3-state buffers associated with each CLB, that can be accessed by all the outputs of a CLB.
Xilinx is the only major FPGA vendor that provides dedicated resources for on-chip 3-state bussing. This feature can increase the performance and lower the CLB utilization for wide multiplex functions. The Xilinx internal bus can also be extended off chip.

15. Xilinx CLB Slice
The Design Warrior’s Guide to FPGAs Devices, Tools, and Flows. ISBN Copyright © 2004 Mentor Graphics Corp. (

16. CLB Slice Structure Each slice contains two sets of the following:
Four-input LUT
Any 4-input logic function,
or 16-bit x 1 sync RAM (SLICEM only)
or 16-bit shift register (SLICEM only)
Carry & Control
Fast arithmetic logic
Multiplier logic
Multiplexer logic
Storage element
Latch or flip-flop
Set and reset
True or inverted inputs
Sync. or async. control
Two slices form a CLB. These slices can be used independently or together for wider logic functions.Within each slice also, the LUT and the flip flop can be used for the same function or for independent functions. The flip flops do not handcuff the designers into only having a set or clear. And for more ASIC like flows, the flip flop can be sued as latch. So, the designers do not need to re-code the design for the device architecture.

17. LUT (Look-Up Table) Functionality
Look-Up tables are primary elements for logic implementation
Each LUT can implement any function of 4 inputs

18. 5-Input Functions implemented using two LUTs
One CLB Slice can implement any function of 5 inputs
Logic function is partitioned between two LUTs
F5 multiplexer selects LUT

19. 5-Input Functions implemented using two LUTs
OUT
LUT

20. Xilinx Multipurpose LUT
The Design Warrior’s Guide to FPGAs Devices, Tools, and Flows. ISBN Copyright © 2004 Mentor Graphics Corp. (

21. Simplified view of a Xilinx Logic Cell
The Design Warrior’s Guide to FPGAs Devices, Tools, and Flows. ISBN Copyright © 2004 Mentor Graphics Corp. (

22. Distributed RAM = or CLB LUT configurable as Distributed RAM
RAM16X1S O D WE
WCLK A0 A1 A2 A3
RAM32X1S A4
RAM16X2S O1 D0 D1 O0 =
LUT or
RAM16X1D
SPO
DPRA0
DPO
DPRA1
DPRA2
DPRA3
CLB LUT configurable as Distributed RAM
A single LUT equals 16x1 RAM
Two LUTs Implement Single and Dual-Port RAMs
Cascade LUTs to increase RAM size
Synchronous write
Synchronous/Asynchronous read
Accompanying flip-flops used for synchronous read
When the CLB LUT is configured as memory, it can implement 16x1 synchronous RAM. One LUT can implement 16x1 Single-Port RAM. Two LUTs are used to implement 16x1 dual port RAM. The LUTs can be cascaded for desired memory depth and width.
The write operation is synchronous. The read operation is asynchronous and can be made synchronous by using the accompanying flip flops of the CLB LUT.
The distributed ram is compact and fast which makes it ideal for small ram based functions.

23. Shift Register = Each LUT can be configured as shift registerQ CE
LUT IN
CLK
DEPTH[3:0]
OUT =
Each LUT can be configured as shift register
Serial in, serial out
Dynamically addressable delay up to 16 cycles
For programmable pipeline
Cascade for greater cycle delays
Use CLB flip-flops to add depth
The LUT can be configured as a shift register (serial in, serial out) with bit width programmable from 1 to 16. For example, DEPTH[3:0] = 0010(binary) means that the shift register is 3-bit wide. In the simplest case, a 16 bit shift register can be implemented in a LUT, eliminating the need for 16 flip flops, and also eliminating extra routing resources that would have been lowered the performance otherwise.

24. Shift Register Register-rich FPGA64
Operation A
4 Cycles
8 Cycles
Operation B
3 Cycles
Operation C
12 Cycles
9-Cycle imbalance
Register-rich FPGA
Allows for addition of pipeline stages to increase throughput
Data paths must be balanced to keep desired functionality
In this example, there is a cycle imbalance, which must be fixed. Let’s think of how the shift register can fix the imbalanced cycles. As seen from the slide, the logic will be off by nine clock cycles.

25. Carry & Control Logic SLICE Carry & Control Logic Carry & Control
COUT YB
Look-Up
Table
Carry
&
Control
Logic Y G4 G3 G2 G1 S D Q O CK EC R
F5IN BY SR XB
Look-Up
Table
Carry
&
Control
Logic X S F4 F3 F2 F1 D Q O
The configurable logic block (CLB) contains two slices. Each slice contains two 4-input look-up tables (LUT), carry & control logic and two registers. There are two 3-state buffers associated with each CLB, that can be accessed by all the outputs of a CLB.
Xilinx is the only major FPGA vendor that provides dedicated resources for on-chip 3-state bussing. This feature can increase the performance and lower the CLB utilization for wide multiplex functions. The Xilinx internal bus can also be extended off chip. CK EC R
CIN
CLK CE
SLICE

26. Fast Carry Logic
Each CLB contains separate logic and routing for the fast generation of sum & carry signals
Increases efficiency and performance of adders, subtractors, accumulators, comparators, and counters
Carry logic is independent of normal logic and routing resources
MSB
Carry Logic
Routing
LSB

27. Accessing Carry Logic
All major synthesis tools can infer carry logic for arithmetic functions
Addition (SUM <= A + B)
Subtraction (DIFF <= A - B)
Comparators (if A < B then…)
Counters (count <= count +1)

28. Input/Output Blocks (IOBs)

29. Basic I/O Block Structure
Three-State D Q
FF Enable EC
Three-State Control
Clock SR
Set/Reset
Output D Q
FF Enable EC
Output Path SR
Direct Input
FF Enable
Input Path
Registered Input Q D EC SR

30. IOB Functionality
IOB provides interface between the package pins and CLBs
Each IOB can work as uni- or bi-directional I/O
Outputs can be forced into High Impedance
Inputs and outputs can be registered
advised for high-performance I/O
Inputs can be delayed

31. Other Components of Spartan 3 FPGAs

32. RAM Blocks and Multipliers in Xilinx FPGAs
The Design Warrior’s Guide to FPGAs Devices, Tools, and Flows. ISBN Copyright © 2004 Mentor Graphics Corp. (

33. A simple clock tree
The Design Warrior’s Guide to FPGAs Devices, Tools, and Flows. ISBN Copyright © 2004 Mentor Graphics Corp. (

34. Digital Clock Manager (DCM)
The Design Warrior’s Guide to FPGAs Devices, Tools, and Flows. ISBN Copyright © 2004 Mentor Graphics Corp. (

35. Spartan-3 Family Attributes

36. Spartan-3 FPGA Family Members

37. FPGA Nomenclature

38. FPGA device present on the RC10 board
XC3S1500-4FG320
Spartan 3
family
1500 k
= 1.5 M
equivalent
logic gates
speed
grade -4
= standard
performance
320 pins
package type

39. FPGA Design Flow

40. Design flow (1) Specification (Lab Experiments)
Design and implement a simple unit permitting to speed up encryption with RC5-similar cipher with fixed key set on 8031 microcontroller. Unlike in the experiment 5, this time your unit has to be able to perform an encryption algorithm by itself, executing 32 rounds…..
Specification (Lab Experiments)
VHDL description (Your Source Files)
Library IEEE;
use ieee.std_logic_1164.all;
use ieee.std_logic_unsigned.all;
entity RC5_core is
port(
clock, reset, encr_decr: in std_logic;
data_input: in std_logic_vector(31 downto 0);
data_output: out std_logic_vector(31 downto 0);
out_full: in std_logic;
key_input: in std_logic_vector(31 downto 0);
key_read: out std_logic; );
end AES_core;
Functional simulation
Synthesis
Post-synthesis simulation

41. Design flow (2) Implementation Timing simulation Configuration
On chip testing

42. Tools used in FPGA Design Flow
Functionally verified
VHDL code
Design
VHDL code
Synplicity
Synplify Pro
Xilinx XST
Synthesis
Netlist
Implementation
Xilinx ISE
Bitstream

43. Synthesis

44. Synthesis Tools
Xilinx XST
Synplify Pro
… and others

45. Logic Synthesis VHDL description Circuit netlist
architecture MLU_DATAFLOW of MLU is
signal A1:STD_LOGIC;
signal B1:STD_LOGIC;
signal Y1:STD_LOGIC;
signal MUX_0, MUX_1, MUX_2, MUX_3: STD_LOGIC;
begin
A1<=A when (NEG_A='0') else
not A;
B1<=B when (NEG_B='0') else
not B;
Y<=Y1 when (NEG_Y='0') else
not Y1;
MUX_0<=A1 and B1;
MUX_1<=A1 or B1;
MUX_2<=A1 xor B1;
MUX_3<=A1 xnor B1;
with (L1 & L0) select
Y1<=MUX_0 when "00",
MUX_1 when "01",
MUX_2 when "10",
MUX_3 when others;
end MLU_DATAFLOW;

46. Circuit netlist (RTL view)

47. Mapping
LUT0
LUT4
LUT1
FF1
LUT5
LUT2
FF2
LUT3

48. RTL view in Synplify Pro
General logic structures can be recognized in RTL view
comparator
incrementer
MUX

49. Crossprobing between RTL view and code
Each port, net or block can be chosen by mouse click from the browser or directly from the RTL View
By double-clicking on the element its source code can be seen:
Reverse crossprobing is also possible: if section of code is marked, appropriate element of RTL View is marked too:

50. Technology View in Synplify Pro
Technology view is a mapped RTL view. It can be seen by pressing button or by double-click on “.srm” file
As in case of “RTL View”, buttons can be used here
Two additional buttons are enabled: show critical path
- open timing analyst
Pay attention: technology view is usually large and presented on number of sheets
Technology view is presented using device primitives
Ports, nets and blocks browser

51. Viewing critical path Critical path can be viewed by pressing on
Delay values are written near each component of the path

52. Timing Analyst Timing analyst opened by pressing on
Timing analyst gives a possibility to analyze different paths in the design
Timing analyst can be opened only from Technology View

53. Implementation

54. Implementation
After synthesis the entire implementation process is performed by FPGA vendor tools

56. Translation Circuit netlist Timing Constraints Native Constraint File
Synthesis
Circuit netlist
Timing Constraints
Constraint Editor
or Text Editor
Native
Constraint
File
Electronic Design
Interchange Format
EDIF
NCF
UCF
User Constraint File
Translation
NGD
Native Generic Database file

57. Mapping
LUT0
LUT4
LUT1
FF1
LUT5
LUT2
FF2
LUT3

58. Placing
FPGA
CLB SLICES

59. Routing
FPGA
Programmable Connections

60. Configuration
Once a design is implemented, you must create a file that the FPGA can understand
This file is called a bit stream: a BIT file (.bit extension)
The BIT file can be downloaded directly to the FPGA, or can be converted into a PROM file which stores the programming information

61. Two main stages of the FPGA Design Flow
Synthesis
Implementation
Technology
dependent
Technology
independent
RTL
Synthesis
Map
Place & Route
Configure
Code analysis
- Derivation of main logic constructions
Technology independent optimization
Creation of “RTL View”
Mapping of extracted logic structures to device primitives
Technology dependent optimization
Application of “synthesis constraints”
Netlist generation
Creation of “Technology View”
Placement of generated netlist onto the device
Choosing best interconnect structure for the placed design
Application of “physical constraints”
Bitstream generation
Burning device

62. Report files
ECE 448 – FPGA and ASIC Design with VHDL

63. Map report header Release 8.1i Map I.24
Xilinx Mapping Report File for Design 'Lab3Demo'
Design Information
Command Line : c:\Xilinx\bin\nt\map.exe -p 3S1500FG o map.ncd -pr b -k 4
-cm area -c 100 Lab3Demo.ngd Lab3Demo.pcf
Target Device : xc3s1500
Target Package : fg320
Target Speed : -4
Mapper Version : spartan3 -- $Revision: 1.34 $
Mapped Date : Tue Feb 13 17:04:

64. Map report Design Summary -------------- Number of errors: 0
Number of warnings: 0
Logic Utilization:
Number of Slice Flip Flops: out of 26, %
Number of 4 input LUTs: out of 26, %
Logic Distribution:
Number of occupied Slices: out of 13, %
Number of Slices containing only related logic: out of %
Number of Slices containing unrelated logic: out of %
*See NOTES below for an explanation of the effects of unrelated logic
Total Number 4 input LUTs: out of 26, %
Number used as logic:
Number used as a route-thru:
Number of bonded IOBs: out of %
IOB Flip Flops:
Number of GCLKs: out of %

65. Place & route report
Asterisk (*) preceding a constraint indicates it was not met.
This may be due to a setup or hold violation.
Constraint | Requested | Actual | Logic | Absolute |Number of
| | | Levels | Slack |errors
* TS_CLOCK = PERIOD TIMEGRP "CLOCK" 5 ns | 5.000ns | 5.140ns | | ns | 5
HIGH 50% | | | | |
TS_gen1Hz_Clock1Hz = PERIOD TIMEGRP "gen1 | 5.000ns | 4.137ns | | 0.863ns | 0
"gen1Hz_Clock1Hz" 5 ns HIGH 50% | | | | |

66. Post layout timing report
Clock to Setup on destination clock CLOCK
| Src:Rise| Src:Fall| Src:Rise| Src:Fall|
Source Clock |Dest:Rise|Dest:Rise|Dest:Fall|Dest:Fall|
CLOCK | | | | |
Timing summary:
Timing errors: 9 Score: 543
Constraints cover 574 paths, 0 nets, and 187 connections
Design statistics:
Minimum period: ns (Maximum frequency: MHz)