PROGRAMMABLE LOGIC
DESIGN WITH VHDL
Objectives
 Upon completion of this training, your VHDL knowledge will enable
you to:
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Implement efficient combinatorial and sequential logic
Design state machines and understand implementation trade-offs
Use hierarchy / Create reusable components
Identify how VHDL will synthesize and fit into a PLD, CPLD
and FPGA
Objectives (contd.)
 Upon completion of this training, you will be able to use Warp to:
 Compile and synthesize VHDL designs for programmable
logic devices
 Create VHDL or Verilog timing simulation models for
popular third party simulators.
 Target PLDs/CPLDs
• Simulate the resulting device with the Aldec full timing
simulator
• Use the report file to determine operating frequency, setup time, clock to output delay, and device resource usage.
Agenda
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Intro, Why Use VHDL?,
Design Flow
VHDL Design Descriptions
The Entity, Ports, Modes, Types
Exercise #1 - Write an entity statement
The Architecture, differing styles
Concurrent and Sequential statements
Processes: Signals vs. Variables
VHDL Operators/Overloading/Inferencing
VHDL Identifiers
Exercise #2 - write an architecture
Tri-State Logic, Don't Cares
Warp GUI overview
Exercise #3 - Design a bus controller
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Aggregates and Subscripts
Registers, Latches and Implicit Memory
Exercise #4 - Design a counter
Lunch
State Machines and State Encoding
Exercise #5 - Design a state machine
Design Hierarchy - components, pkg’s, libraries
Exercise #6 - Design a loadable counter hierarchy
Generate Statement
Multiplexing I/O pins
Exercise #7 - DRAM output controller
User defined attributes
CPLD synthesis directives
Miscellaneous Topics and Wrap-up
Introduction
 VHDL is used to:
 document circuits
 simulate circuits
 synthesize design descriptions
 Synthesis is the reduction of a design description to a lowerlevel representation (such as a netlist or a set of equations).
 This training course covers VHDL for PLD synthesis
 The course will at times draw upon the concepts of VHDL as a
simulation language
Why Use VHDL?
 Quick Time-to-Market
 Allows designers to quickly develop designs requiring
tens of thousands of logic gates
 Provides powerful high-level constructs for describing
complex logic
 Supports modular design methodology and multiple levels
of hierarchy
 One language for design and simulation
 Allows creation of device-independent designs that are
portable to multiple vendors. Good for ASIC Migration
 Allows user to pick any synthesis tool, vendor, or device
VHDL vs. Verilog
History
 Developed by DoD in early
80s as means for
Contractors to Describe
Designs-Funded VHSIC
 1987 IEEE ratified 1076
and DoD mandated
VHDL(F-22) and EDA
vendors created tools.
 1993 - IEEE 1076 ‘93
 1996 Commercial Sim and
Synthesis tools become
available and 1164 pkg
enables multi value logic
 1983 -Gateway founded by
Genrad’s HDL and HILO
simulator author.Releases
Verilog HDL and Simulator
 1985 Enhanced VerilogXL-used for high end
designs -Fast Simulator interpretive-no need to
precompile
 1990 Cadence buys
Gateway-nearly all ASIC
foundries used XL as
Golden Simulator
 1995 IEEE 1364
VHDL vs. Verilog
Compilation/Data Types/High Level Constructs/Verbosity/Ease
 Many E-A pairs may reside
in single system file.
 User Can define Data
Types-Powerful
 High Level Modeling w/
Package, Config, Generate
 Strongly Typed Language models must be precisely
coded-often longer code
 Less intuitive but much
more powerful constructs
 Order or Code is crucial to
obtaining desired output.
 Simple Data Types are
controlled by language
 No Equivalent High Level
Modeling Constructs
 Verilog has looser
structure-can lead to
unwanted and unidentified
errors-more concise code.
 Easiest to Grasp-more
prone to create unwanted
results
WARP5.0
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WARP2 Release 5.0 now supports Verilog Synthesis
Same great Synthesis as VHDL
Includes Aldec Full Timing Simulator and FSM Editor
Generates timing simulation models for major third party
VHDL and Verilog simulators
New GUI-Microsoft Std Interface
Even Better HDL Editor
Supports All Cypress Devices
Windows 95, NT, UNIX
Same Great $99 Price
Warp2/Warp3/Programming
Design
Entry
Schematic
Text/FSM
Front
End
Simulation
Synthesis
Design
Compilation
Fitting
Design
Verification
JEDEC
Sim. Model
JAM file
Simulator
ISR/Impulse3
Back
End
VHDL Design Descriptions
 VHDL design descriptions consist of an ENTITY
declaration and an ARCHITECTURE body
 The ENTITY declaration describes the design I/O
 The ARCHITECTURE body describes the
content or function of the design
 Every architecture needs an entity so it is common
to refer to them together as an
ENTITY/ARCHITECTURE PAIR
Example Entity/Architecture Pair:
A 2-Input And Function
ENTITY and2 IS PORT (
a,b :
IN std_logic;
f:
OUT std_logic);
END and2;
ARCHITECTURE behavioral OF and2 IS
BEGIN
f <= a AND b;
END behavioral;
The Entity
 A “BLACK BOX”
 The ENTITY describes the periphery of the
black box (i.e., the design I/O)
BLACK_BOX
rst
q[7:0]
d[7:0]
clk
co
Example Entity declaration
ENTITY black_box IS PORT (
clk, rst:
IN std_logic;
d:
IN std_logic_vector(7 DOWNTO 0);
q:
OUT std_logic_vector(7 DOWNTO 0);
co:
OUT std_logic);
END black_box;
BLACK_BOX
 What does all this mean?
rst
q[7:0]
d[7:0]
clk
co
The Entity Declaration
ENTITY entity_name IS
-- optional generics
PORT (
name : mode type ;
...
) ;
END entity_name;
 entity_name is an arbitrary name
 generics are used for defining parameterized components
 name is the signal/port identifier and may be a comma
separated list for ports of identical modes and types
 mode describes the direction the data is flowing
 type indicates the set of values name may be assigned
Ports
 The Entity (“BLACK BOX”) has PORTS
 PORTS are the points of communication
• PORTS are usually the device pins
 PORTS have an associated name, mode, and type
Port Modes
A port’s MODE indicates the direction that data is transferred:
Entity
 IN
Data goes into the entity only
 OUT
Data goes out of the entity only
(and is not used internally)
 INOUT
Data is bi-directional (goes into
and out of the entity)
 BUFFER Data that goes out of the entity
and is also fed-back internally
IEEE 1076 Types
 VHDL is a strongly typed language (you cannot assign a signal of
one type to the signal of another type)
 bit - a signal of type bit that can only take values of '0' or '1'
 bit_vector - a grouping of bits (each can be '0' or '1')
SIGNAL
SIGNAL
a: BIT_VECTOR(0 TO 3);
-- ascending range
b: BIT_VECTOR(3 DOWNTO 0); -- descending range
a <= "0111"; -- double quotes used for vectors
b <= "0101";
This means that:
a(0) = '0'
b(0) = '1'
a(1) = '1'
b(1) = '0'
a(2) = '1'
b(2) = '1'
a(3) = '1'
b(3) = '0'
IEEE 1076 TYPES (contd.)
 INTEGER
• useful as index holders for loops, constants, generics,
or high-level modeling
 BOOLEAN
• can take values ‘TRUE’ or ‘FALSE’
 ENUMERATED
• has user defined set of possible values, e.g.,
• TYPE traffic_light IS (green, yellow, red);
IEEE 1164
 A package created to solve the limitations of the BIT type
 Nine values instead of just two ('0' and '1')
 Allows increased flexibility in VHDL coding, synthesis, and
simulation
 STD_LOGIC and STD_LOGIC_VECTOR are used instead
of BIT and BIT_VECTOR when a multi-valued logic
system is required
 STD_LOGIC and STD_LOGIC _VECTOR must be used
when tri-state logic (Z) is required
 To be able to use this new type, you need to add 2 lines to
your code:
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
1164 Types
 std_logic and std_logic_vector are the industry
standard logic type for digital design
 Values for Simulation & Synthesis
 ‘0’ -- Forcing ‘0’
 ‘1’ -- Forcing ‘1’
 ‘Z’ -- High Impedance
 ‘L’ -- Weak ‘0’
 ‘H’ -- Weak ‘1’
 ‘-’
-- Don’t care
 Values for Simulation only (std_ulogic):
 ‘U’ -- Uninitialized
 ‘X’ -- Forcing Unknown
 ‘W’ -- Weak Unknown
Entity Declaration Example
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY black_box IS PORT (
clk, rst:
IN std_logic;
d:
IN std_logic_vector(7 DOWNTO 0);
q:
OUT std_logic_vector(7 DOWNTO 0);
co:
OUT std_logic);
END black_box;
BLACK_BOX
MODE
TYPE
rst
q[7:0]
d[7:0]
clk
co
Exercise #1: The Entity - A Walk through
 Write an entity declaration for the following:
Port D is a 12-bit bus, input only
Port OE and CLK are each input bits
Port AD is a 12-bit, three-state bi-directional bus
Port A is a 12-bit bus, output only
Port INT is a three-state output
Port AS is an output also used internally
my_design
d[11:0]
oe
clk
ad[11:0]
a[11:0]
int
as
Exercise #1: Solution
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY my_design IS PORT (
d:
IN std_logic_vector(11 DOWNTO 0);
oe, clk: IN std_logic;
ad:
INOUT std_logic_vector(11 DOWNTO 0);
a:
OUT std_logic_vector(11 DOWNTO 0);
int:
OUT std_logic;
my_design
as:
BUFFER std_logic);
END my_design;
ad[11:0]
d[11:0]
-- In this presentation, VHDL keywords
a[11:0]
oe
-- are highlighted in bold, CAPITALS;
int
clk
as
-- however, VHDL is not case sensitive:
-- clock, Clock, CLOCK all refer to the
-- same signal, -- means a comment
The Architecture
 Architectures describe what is in the black box (i.e., the
structure or behavior of entities)
 Descriptions can be either a combination of
 Structural descriptions
• Instantiations (placements of logic-much like in a
schematic-and their connections) of building blocks
referred to as components
 Behavioral/Dataflow descriptions
• Algorithmic (or “high-level”) descriptions:
IF a = b THEN state <= state5;
• Boolean equations (also referred to as dataflow):
x <= a OR (b AND c);
The Architecture Declaration
ARCHITECTURE arch_name OF entity_name IS
-- optional signal declarations, etc.
BEGIN
--VHDL statements
END arch_name;
 arch_name is an arbitrary name
 optional signal declarations are used for signals local to
the architecture body (that is, not the entity’s I/O).
 entity_name is the entity name
 statements describe the function or contents of the entity
Architecture Body Styles : Behavioral
ENTITY compare IS PORT (
a, b:
IN std_logic_vector(0 TO 3);
equals: OUT std_logic);
END compare;
ARCHITECTURE behavior OF compare IS
BEGIN
comp: PROCESS (a,b)
BEGIN
IF a = b THEN
equals <= '1' ;
ELSE
equals <= '0' ;
END IF ;
END PROCESS comp;
END behavior;
Architecture Body Styles : Dataflow
ENTITY compare IS PORT (
a, b:
IN std_logic_vector(0 TO 3);
equals: OUT std_logic);
END compare;
ARCHITECTURE dataflow OF compare IS
BEGIN
equals <= '1' WHEN a = b ELSE '0' ;
END dataflow;
Architecture Body Styles : Structural
ENTITY compare IS PORT (
a, b:
IN std_logic_vector(0 TO 3);
equals: OUT std_logic);
END compare;
USE WORK.gatespkg.ALL ;
ARCHITECTURE structure OF compare IS
SIGNAL x : std_logic_vector (0 to 3) ;
BEGIN
u0: xnor2 PORT MAP (a(0),b(0),x(0)) ;
u1: xnor2 PORT MAP (a(1),b(1),x(1)) ;
u2: xnor2 PORT MAP (a(2),b(2),x(2)) ;
u3: xnor2 PORT MAP (a(3),b(3),x(3)) ;
u4: and4 PORT MAP (x(0),x(1),x(2),x(3),equals) ;
END structure;
Mixing Architecture Styles
 The various styles may be mixed in one architecture.
ENTITY logic IS PORT (
a,b,c: IN std_logic;
f:
OUT std_logic);
END logic;
LOGIC
a
b
d
c
USE WORK.gatespkg.ALL;
ARCHITECTURE archlogic OF logic IS
SIGNAL d: std_logic;
BEGIN
Behavioral/Dataflow
d <= a AND b;
Structural
g1: nor2 PORT MAP (c, d, f);
END archlogic;
g1
f
Comparing Architecture Styles
 These examples synthesize to equivalent circuits
 In more elaborate designs, some descriptions may yield
more efficient circuits
 sloppy code = inefficient results (see section 3.3.4)
 Use styles that make your designs easier to describe and
maintain
 Behavioral/Dataflow exploit module generation
(described later)
 Structural descriptions may make the design less
portable (may rely on a library of vendor-specific
components)
Module Generation
 In Warp release 4.0, a package called ‘std_arith’ can be
used to overload the arithmetic (+, -, etc.) and relational
operators (=, /=, <, etc.,) for std_logic, std_logic_vector
and integer types
 Using this package causes adders, counters,
comparators, etc., to automatically replace the
operators in the design. These are optimized for the
target architecture and synthesis goal (area/speed)
• This is known as module generation
Ultragen Synthesis
if (a = b) then c <= ‘1’;
end if;
Speed
Speed
Adders
Speed
Adders
Subtractors
Subtractors
Adders
Adders
Subtractors
Subtractors
Multipliers
Multipliers
Subtractors
Subtractors
Multipliers
Multipliers
Comparator
Comparator
Multipliers
Multipliers
s
Comparators
s
Comparators
Comparators
Comparators
Counters
Counters
Counters
Counters
Counters
Counters
Shifters
Shifters
Shifters
Shifters
Shifters
Shifters
FUltra39000
LASH370i
Ultra37000
Ultra37000
c <= ‘0’;
Area
Area
Adders
Area
Adders
FLASH370i
else
Pre-optimized Circuits
Ultra39000
The VHDL code
below describes
a comparator
Warp chooses the best pre-optimized
circuit to meet your design goals
A Simple Counter
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE WORK.std_arith.ALL;
clk
ENTITY count8 IS PORT (
clk: IN std_logic;
count: BUFFER std_logic_vector(7 DOWNTO 0));
END count8 ;
ARCHITECTURE arch_count8 OF count8 IS
BEGIN
upcount: PROCESS (clk)
BEGIN
IF clk’EVENT and clk=‘1’
THEN count <= count + 1;
END IF;
END PROCESS upcount;
END arch_count8;
count
VHDL Statements
 There are two types of statements, Concurrent and Sequential
 Concurrent Statements (means in parallel)
 Concurrent statements are “executed” concurrently (at
the same time)
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The order of concurrent statements is not important

Most of the examples we have seen so far have been
concurrent statements:
– Boolean Equations
– WHEN-ELSE
– WITH-SELECT-WHEN
VHDL Statements (cont.)
 Sequential Statements (means in series)
 Sometimes we need to model complex functions.
In that case, we can use an “algorithm” or model
to describe the function. This is done with
Sequential Statements

With Sequential statements, the ORDER of the
statements is important (example later)

Therefore, we use a process to mark the
beginning and end of a block of sequential
statements

Each completed process is considered to be one
big concurrent statement (there can be many
processes inside one architecture)
What is a VHDL “Process” ?
 Processes are either awake or asleep (active or inactive)
 A process normally has a sensitivity list
 When a signal in that sensitivity list changes value, the
process wakes up and all of the sequential statements
are “executed”
 For example, a process with a clock signal in its
sensitivity list will become active on changes of the
clock signal
 At the end of the process, all outputs are assigned and the
process goes back to sleep until the next time a signal
changes in the sensitivity list
The Process (contd.)
label: PROCESS (sensitivity list)
-- variable declarations
BEGIN
-- sequential statements
END PROCESS label ;
 The process label and variable declarations are
optional
 The process executes when one of the signals in the
sensitivity list has an event
Combinational Logic
 Can be described with concurrent statements
 boolean equations
 when-else
 with-select-when
 component instantiatons
 Can be described with sequential statements
 if-then-else
 case-when
Combinational Logic w/ Boolean Equations
 Boolean Equations can be used in both concurrent
and sequential signal assignment statements.
 A 4-1 multiplexer is shown below
s
x <= (a AND NOT(s(1)) AND NOT(s(0))) OR
(b AND NOT(s(1)) AND s(0)) OR
(c AND s(1) AND NOT(s(0))) OR
(d AND s(1) AND s(0)) ;
2
a
b
c
d
mux
x
Selective Signal Assignment:
with-select-when
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Assignment based on a selection signal
WHEN clauses must be mutually exclusive
Use a WHEN OTHERS when all conditions are not specified
Only one reference to the signal, only one assignment operator (<=)
WITH selection_signal SELECT
signal_name <= value_1 WHEN value_1 of selection_signal,
value_2 WHEN value_2 of selection_signal,
...
value_n WHEN value_n of selection_signal,
value_x WHEN OTHERS;
Combinational Logic w/
Selective Signal Assignment
 The same 4-1 multiplexer is shown below
with s select
x <= a when “00” ,
b when “01” ,
c when “10” ,
d when others ;
s
2
a
b
c
d
mux
x
More on with-select-when
 You can use a range of values
with int_value select
x <= a when 0 to 3,
b when 4 | 6 | 8 ,
c when 10 ,
d when others ;
Conditional Signal Assignment:
when-else

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
Signal is assigned a value based on conditions
Any simple expression can be a condition
Priority goes in order of appearance
Only one reference to the signal, only one assignment
operator (<=)
 Use a final ELSE to avoid latches
signal_name <= value_1
value_2
...
value_n
value_x
WHEN condition1 ELSE
WHEN condition2 ELSE
WHEN condition N ELSE
;
Combinational Logic w/
Conditional Signal Assignment
 The same 4-1 multiplexer is shown below
x <= a when (s = “00”) else
b when (s = “01”) else
c when (s = “10”) else
d;
s
2
a
b
c
d
mux
x
Combinational Logic w/
Conditional Signal Assignment
 The when conditions do not have to be mutually
exclusive (as in with-select-when)
 A priority encoder is shown below
j <= w when (a = ‘1’) else
x when (b = ‘1’) else
y when (c = ‘1’) else
z when (d = ‘1’) else
“000” ;
Combinatorial Logic
w/ Sequential Statements
 Grouped together with Processes
 Processes are concurrent with one another and with
concurrent statements
 Order of sequential statements does make a
difference in synthesis
Sequential Statements: if-then-else
 Used to select a set of statements to be executed
 Selection based on a boolean evaluation of a
condition or set of conditions
 Absence of ELSE results in implicit memory
IF condition(s) THEN
do something;
ELSIF condition_2 THEN -- optional
do something different;
ELSE
-- optional
do something completely different;
END IF ;
if-then-else
 4-1 mux shown below
mux4_1: process (a, b, c, d, s)
begin
if s = “00” then x <= a ;
elsif s = “01” then x <= b ;
elsif s = “10” then x <= c ;
else x <= d ;
end if;
end process mux4_1 ;
s
2
a
b
c
d
mux
x
Sequential Statements: Case-When
CASE selection_signal IS
WHEN value_1_of_selection_signal =>
(do something)
-- set of statements 1
WHEN value_2_of_selection_signal =>
(do something)
-- set of statements 2
...
WHEN value_N_of_selection_signal =>
(do something)
-- set of statements N
WHEN OTHERS =>
(do something)
-- default action
END CASE ;
The CASE Statement: 4-1 Mux
ARCHITECTURE archdesign OF design IS
SIGNAL s: std_logic_vector(0 TO 1);
BEGIN
mux4_1: PROCESS (a,b,c,d,s)
BEGIN
CASE s IS
WHEN "00" => x <= a;
WHEN "01" => x <= b;
WHEN "10” => x <= c;
WHEN OTHERS => x <= d;
END CASE;
END PROCESS mux4_1;
END archdesign;
s
2
a
b
c
d
mux
x
Signal Assignment in Processes
Which Circuit is Correct?
ARCHITECTURE arch_reg OF reg IS
SIGNAL b: std_logic
reg2: PROCESS
BEGIN
WAIT UNTIL clock = '1' ; -- implied sensitivity list
b <= a;
c <= b;
-- after the rising clock edge, a goes to b
-- after the rising clock edge, b goes to c
END PROCESS reg2;
END arch_reg
a
a
c
clock
clock
b
c
Signal Assignment in Processes
 Inside processes, signals are not updated immediately.
Instead, they are scheduled to be updated
 The signals are not actually updated until the END
PROCESS statement is reached
 Therefore, on the previous slide, two registers will be
synthesized (c <= b will be the old b)
 In some cases, the use of a concurrent statement outside
the process will fix the problem, but this is not always
possible
 So how else can we fix this problem ?
Variables
 When a concurrent signal assignment outside the
process cannot be used, the previous problem can be
avoided using a variable
 Variables are like signals, BUT they can only be
used inside a PROCESS. They cannot be used to
communicate information between processes
 Variables can be of any valid VHDL data type
 The value assigned to a variable is available
immediately
 Assignment of variables is done using a colon (:),
like this:
c := a AND b;
Using Variables vs. Signals
 Solution using a variable within a process:
-- assume a and c are signals defined elsewhere
ARCHITECTURE arch_reg OF reg IS
PROCESS
VARIABLE b: std_logic ;
BEGIN
WAIT UNTIL clock = '1' ;
b := a ; -- this is immediate
c <= b ; -- this is scheduled
END PROCESS ;
END arch_reg;
Native Operators
 Logical - defined for type bit, bit_vector, boolean*
 AND, NAND
 OR, NOR
 XOR, XNOR
 NOT
 Relational - defined for types bit, bit_vector, integer*
 = (equal to)
 /= (not equal to)
 < (less than)
 <= (less than or equal to)
 > (greater than)
 >= (greater than or equal to)
 * overloaded for std_logic, std_logic_vector
Native Operators (contd.)
 Unary Arithmetic - defined for type integer*
 - (arithmetic negate)
 Arithmetic - defined for type integer*
 + (addition), * (multiplication)
 - (subtraction)
 Concatenation - defined for strings
 &
Note, a STRING is any sequence of characters, therefore a
std_logic_vector is an example of a STRING
 * overloaded for std_logic, std_logic_vector
Overloaded Operators
 In VHDL, the scope of all of the previous operators
can be extended (or overloaded) to accept any type
supported by the language, e.g.,
-----
assume a declaration of a 16-bit vector as
SIGNAL pc IS std_logic_vector(15 DOWNTO 0);
then a valid signal assignment is
pc <= pc + 3;
assuming the '+' operator has been overloaded to accept std_logic_vector and integer operands
 The std_logic_1164 package defines overloaded
logical operators (AND, OR, NOT, etc.,) for the
std_logic and std_logic_vector types
 In this training, you will learn to use overloaded
operators, but not to define them
Legal VHDL Identifiers
 Letters, digits, and underscores only (first character must
be a letter)
 The last character cannot be an underscore
 Two underscores in succession are not allowed
 Using reserved words is not allowed (the VHDL editor
will highlight reserved words for this reason)
 Examples
 Legal
• tx_clk, Three_State_Enable, sel7D, HIT_1124
 Not Legal
• _tx_clk, 8B10B, large#num, case, clk_
The Warp Design Environment
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

Using the Project Wizard
Entering Project Name / Path
Adding Files to the Project
Selecting a Device
Opening up a File for Editing
Additional Tools Review
 Describing the left hand files pane
 Overview of Pull down menus
 Reviewing On-line Help
Using the Project Wizard
 Open Galaxy
 Using the <file> pull down menu, select <new>
 Select “Project - Target Device”, then <ok>
Entering Project Name / Path
 In the Project Name dialog box, enter “exercise2”, then <ok>
 In the Project Path dialog box, browse to “C:\warp\class”,
then select <next>
Adding Files to the Project
 Highlight “ex2.vhd”, select <add> then <ok>
Selecting a Device
 Double click on “Small PLDs”
 Select “22V10” on the left and “PALCE22V10-5JC” on the
right, then hit <finish>, then <ok>
Opening up a File for Editing
 In the left hand pane, double click on “ex2.vhd”.
This will open the file up in the editor on the right
Exercise #2: Architecture
Declaration of a Comparator
 The entity declaration is as follows:
a(3:0)
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
b(3:0)
ENTITY compare IS PORT (
a, b: IN std_logic_vector(3 DOWNTO 0);
aeqb: OUT std_logic);
END compare;
 Write an architecture that causes aeqb to be asserted
when a is equal to b
 Multiple solutions exist
aeqb
Three possible solutions
 Concurrent statement solution using a conditional
assignment:
ARCHITECTURE arch_compare OF compare IS
BEGIN
aeqb <= '1' WHEN a = b ELSE '0';
END arch_compare;
 Concurrent statement solution using boolean
equations:
ARCHITECTURE arch_compare OF compare IS
BEGIN
aeqb <= NOT(
(a(0) XOR b(0)) OR
(a(1) XOR b(1)) OR
(a(2) XOR b(2)) OR
(a(3) XOR b(3)));
END arch_compare;
Three possible solutions (contd.)
 Solution using a process with sequential statements:
ARCHITECTURE arch_compare OF compare IS
BEGIN
comp: PROCESS (a, b)
BEGIN
IF a = b THEN
aeqb <= '1';
a(0 TO 3)
ELSE
aeqb <= '0';
b(0 TO 3)
END IF;
END PROCESS comp;
END arch_compare;
aeqb
Using Tri-State Logic
ENTITY test_three IS
PORT( oe
: IN std_logic;
data
: OUT std_logic_vector(0 to 7));
END test_three;
ARCHITECTURE archtest_three OF test_three IS
BEGIN
PROCESS (oe)
BEGIN
IF (oe = '1')
THEN data <= "01100100";
ELSE data <= "ZZZZZZZZ";
END IF;
END PROCESS;
END archtest_three;
Behavioral Don’t Cares
 Warp uses explicit "don’t care" conditions to produce
optimal logic equations
IF (a = '1') AND (b = '1') THEN
x <= c;
ELSE
x <= '-';
END IF;
 Produces the equation x = c
 To assign don’t cares in VHDL: mysig <= '-';
 'X' means "unknown" and is not useful for
synthesis
Comparing Vectors to Strings
-more on don't cares



Comparing "1101" to "11-1" will return FALSE
Use std_match(a,"string")
Must include std_arith package
Example:
...
signal a : std_logic_vector (1 to 4) ;
...
IF std_match(a,"10-1") THEN
x <= '1' ;
END IF ;
Additional Tools Review
 Describing the left hand files pane
 Source File Listing
 Design Hierarchy
 Output File Listing
 Pull down menus
 File, Edit, View, Format, Project, Compile,
Templates, Bookmarks, Tools, Window, Help
 On-line Help
Source File Listing
 Click on the leftmost tab on the bottom of
the left hand pane
 All source files for the current project
will be displayed
 Double click on any file to open it up in
the editor window on the right
Hierarchy Listing
 Click on the centermost tab on the bottom
of the left hand pane
 The project hierarchy will be displayed
Output File Listing
 Click on the rightmost tab on the bottom
of the left hand pane
 All output files for the current project
will be displayed
 Double click on any file to open it up in
the editor window on the right
 By selecting a sub-heading within a file,
the editor will go to that section
Lower Status Windows
 The lower window pane of Galaxy displays the following
 Compiler - A line by line account of the entire compilation
process. If an error is shown, you can jump into the proper
file and line by double clicking on the error.
 Errors & Warnings - This tab only shows errors & warnings
 Search in files - Shows all occurrences generated by search
in files
button
Pull-down Menus
 Files Menu - Allows the opening or
closing of files and projects, printing, and
recalling of prior files and projects
Pull-down Menus
 Edit Menu - Typical Cut, Copy and Paste
commands as well as Find, Replace and
Search all files. Additionally, the editor
and project user preferences dialog box
can be selected.
Output File Listing
 The Preferences screen
allows the user to select
editor options such as
autosave, font size, tab
spacing and highlighting.
Additionally, project
settings can be set up as
well
Pull-down Menus
 View Menu - Allows the user to select
several viewing options such as viewing
pane options and toolbars
 Format Menu - Allows block comment /
un-comment as well as the setting of tabs
Pull-down Menus
 Project Menu - Used to add and remove
files from a project and perform library
management. Additionally the user can
select/change device types, set compiler
options, set a project as the top level in a
hierarchy as well as back annotate pins
and nodes to a control file.
Compiler Options
 The Compiler options screen
allows the user to choose
generic attributes for his file
such as area/speed and
optimization effort, I/O
voltage, slew rate and bus
hold. Additionally
technology mapping
attributes can be set. Finally,
the timing model output and
test bench output formats can
be selected.
Pull-down Menus
 Compile Menu - Allows the user to compile
the selected file or the entire project.
 Templates Menu - The user can browse
through VHDL constructs or place LPM
modules within his VHDL code.
 Bookmarks Menu - Allows the user to add
and recall bookmarks within his files.
 Tools Menu - Launches the Jam Composer,
Aldec Simulator and Aldec FSM Editor
Pull-down Menus
 Window Menu - Allows positioning of
files within the edit window as well as
swapping between tabbed windows.
 Help Menu - Access to on-line help and
device selector guide.
Exercise #3:
The Schematic
en(0)
dir
gnd
en(1)
nOE
LE
nOE
LE
control[7:0]
status[7:0]
gnd
dir
CY74FCT373T
en(2)
en(3)
nOE
T/R
CY74FCT373T
nOE
LE
data[7:0]
CY74FCT245T
CY74FCT373T
addr[1:0]
dir
nvalid
en[0:3]
PLD
Exercise #3
 Use Warp to compile the VHDL design description
of the truth table below:
Addr(1:0) nvalid
"00"
"00"
"01"
"01"
"10"
"10"
"11"
"11"
'0'
'1'
'0'
'1'
'0'
'1'
'0'
'1'
en(3) en(2) en(1) en(0) dir
0
0
0
0
0
0
1
0
1
1
1
1
0
1
1
1
0
0
1
0
0
0
0
0
0
1
1
1
1
1
1
1
0
1
1
1
0
1
1
1
 Write the Architecture for the given Entity (next)
 Save design in file named “ex3.vhd”
Exercise #3:
The Entity Declaration
 the entity declaration is as follows:
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY ex3 IS PORT (
addr:
IN std_logic_vector(1 DOWNTO 0);
nvalid: IN std_logic;
en:
BUFFER std_logic_vector(0 TO 3);
dir:
OUT std_logic
);
addr
END ex3;
nvalid
dir
en
PLD
Exercise #3: Instructions
 Create a new project using the Project Wizard
 Choose <file>, <new>, <Project - Target Device>
 Name your project exercise3, click <Next>
 Select the file ex3.vhd and <Add> it to the project
 To choose a device: In the left hand window, double click on
the SPLD folder, then single click on the 22V10 folder. In the
right hand window, select a PALCE22V10-5PC. Note that the
details of the device are outlined below. Click <Finish>
 Double click on the ex3.vhd folder in the left hand window to
open the file up into the editor window on the right.
Exercise #3: Instructions (contd.)
 To designate that ex3.vhd is the top level design, either
choose <Project> <Set Top> or hit the
shortcut button.
 Output an 1164/VHDL timing file by selecting <Project>
<Compiler Options>. In the Simulation Timing Model box,
select 1164/VHDL
 Modify the code in the editor window on the right to
perform the function shown in the prior truth table.
 To compile your design, either choose <Compile>
<Selected> or hit the
shortcut button.
 If an error appear in the lower window, double click on
it to highlight the location of the error in the editor.
 Re-compile until all errors are gone
Exercise #3: Instructions (contd.)
 Simulate the design using the Aldec simulator
 Select <Tools> <Active-HDL Sim>
 Select <File> <Open VHDL> and select
c:\warp\class\vhd\ex3.vhd
 Select <File> <Open Waveform> and select
c:\warp\class\wave_ex3.awf
 Assure the ‘Time To Run’ is 200ns
 Run the simulator <F5> or
 Review against output on the following page
 Reference the application note handout for additional details
Exercise #3: Aldec Simulator Waveform
Exercise #3: The Solution
 The architecture is as follows:
ARCHITECTURE archex3 OF ex3 IS
BEGIN
en(0) <= '0' WHEN (addr = "00" AND nvalid = '0') ELSE '1';
en(1) <= (NOT addr(1)) AND addr(0) AND (NOT nvalid) ;
en(2) <= '0' WHEN (addr = "10" AND nvalid = '0') ELSE '1';
en(3) <= addr(1) AND addr(0) AND (NOT nvalid);
dir <= '0' WHEN (addr = "00" AND nvalid = '0') OR
(addr = "10" AND nvalid = '0') ELSE '1' ;
END archex3;
Aggregates and Subscripts
 An aggregate assignment concatenates signals together
 Good for creating a bus from several inputs
 The concatenation operator can be used as well
tmp <= (a,b,c,d);
tmp <= a & b & c & d;
 Signals can be “pulled” from larger vectors
 Good for grouping outputs as an “alias”
 Sizes on both sides of assignment must match
rw <= ctrl(0); ce <= ctrl(1); oe <= ctrl(2);
highcount <= count(7 DOWNTO 4);
Exercise #3: Alternate Solution
 Using With/Select and aggregates
ARCHITECTURE archex3 OF ex3 IS
SIGNAL control : std_logic_vector(2 DOWNTO 0);
SIGNAL outputs : std_logic_vector(0 TO 4);
BEGIN
control <= addr & nvalid;
WITH control SELECT
outputs <= "00100" WHEN "000",
"10101" WHEN "001",
"11101" WHEN "010",
"10101" WHEN "011",
"10000" WHEN "100",
"10101" WHEN "101",
"10111" WHEN "110",
"10101" WHEN "111",
"-----" WHEN OTHERS;
en <= outputs(0 TO 3);
dir <= outputs(4);
END archex3;
Synchronous Logic
 PLDs work well in synchronous applications
 Two methods of creating synchronous logic
 Structurally
• instantiating components with registers
 Behaviorally
• Using a processes with a clock signal in the
sensitivity list
Registers in Behavioral VHDL
 Example: a D-type flip-flop
ENTITY registered IS PORT (
d, clk:
IN std_logic;
q:
OUT std_logic);
END registered;
ARCHITECTURE archregistered OF registered IS
BEGIN
flipflop: PROCESS (clk)
BEGIN
IF rising_edge(clk)
THEN q <= d;
END IF;
END PROCESS flipflop;
END archregistered;
Registers in Behavioral VHDL
 The synthesis compiler infers that a register is to be created
for which signal q is the output because
 The clock (clk) is in the sensitivity list
 The construct, rising_edge(clk), falling_edge(clk) or
clk’event AND clock=‘1’ appears in the process
 The rising_edge(clk) or falling_edge(clk) statement implies
that subsequent signal assignments occur on the
rising/falling edge of the clock
 The absence of an “else” clause in the “if-then” statement
implies that if the clk’event and clk = ‘1’ condition is not
fulfilled (i.e. not a rising-edge), q will retain its value until
the next assignment occurs (this is referred to as implied
memory)
Rising/Falling Edge Functions
 The 1164 package defines 2 functions for edge detection
 rising_edge (signal)
• similar to (signal’event and signal =‘1’)
 falling_edge (signal)
• similar to (signal’event and signal =‘0’)
if rising_edge(clk) then
q <= d;
end if;
A Registered Process (1)
 A 4-bit counter with synchronous reset
USE WORK.std_arith.ALL;
...
count
upcount: PROCESS (clk)
clk
BEGIN
rst
IF rising_edge(clk) THEN
IF reset = '1'
THEN count <= "0000"; -- or x"0" instead
ELSE count <= count + 1;
END IF;
END IF;
END PROCESS upcount;
 This process is only sensitive to changes in “clk”, i.e.,
it will become active only when the clock transitions
A Registered Process (2)
 A 4-bit counter with asynchronous reset
USE WORK.std_arith.ALL;
...
upcount: PROCESS (clk, reset)
BEGIN
IF reset = '1'
THEN count <= x"0";
ELSIF rising_edge(clk)
THEN count <= count + 1;
END IF;
count
clk
rst
END PROCESS upcount;
 This process is sensitive to changes in both clk and
rst, i.e., it will become active during clock or reset
transitions.
A Registered Process (3)
 A 4-bit loadable counter with asynchronous reset
USE WORK.std_arith.ALL;
...
data
load
upcount: PROCESS (clk, reset)
clk
BEGIN
IF reset = '1’
rst
THEN count <= x"0" ;
ELSIF rising_edge(clk)
THEN
IF load = '1'
THEN count <= data;
ELSE count <= count + 1;
END IF;
END IF;
END PROCESS upcount;
count
Creating a level-sensitive latch
 Instead of using the rising_edge or falling_edge function,
replace it with clk=‘1’ or clk=‘0’ and put d in the
sensitivity list
latch: PROCESS (clk, d)
BEGIN
IF clk = '1'
THEN q <= d;
END IF;
END PROCESS latch;
d
clk
q
Instantiating a registered component
 Example: Using LPM library
LIBRARY ieee;
d
USE ieee.std_logic_1164.ALL;
USE WORK.lpmpkg.all ;
clk
ENTITY registered IS PORT (
d:
IN std_logic;
clk:
IN std_logic_vector(3 DOWNTO 0);
q:
OUT std_logic _vector(3 DOWNTO 0));
END registered;
q
ARCHITECTURE archregistered OF registered IS
BEGIN
flipflop: Mff generic map (lpm_width=>4,lpm_fftype=>lpm_dff)
PORT MAP (data=>d,clock=>clk,enable=>one,q=>q);
END archregistered;
The WAIT statement
 This is another method to activate a process
 The WAIT statement is a sequential statement which
suspends the execution of a process until the
condition specified becomes valid (true)
i.e., an implied sensitivity list, e.g.,
sync: PROCESS
BEGIN
WAIT UNTIL clock='1';
IF enable='1'
THEN q_out <= d_in;
ELSE q_out <= '0';
END IF;
END PROCESS sync;
enable
d_in
clock
D
Q
q_out
Implicit memory
 Signals in VHDL have a current value and may be
scheduled for a future value
 If the future value of a signal cannot be determined, a
latch will be synthesized to preserve its current value
 Advantages:
 Simplifies the creation of memory in logic
design
 Disadvantages:
 Can generate unwanted latches, e.g., when all of
the options in a conditional sequential statement
are not specified
Implicit memory:
Example of incomplete specification
ARCHITECTURE archincomplete OF
incomplete IS
BEGIN
im_mem: PROCESS (a,b)
a
c
BEGIN
IF a = '1'
THEN c <= b;
b
END IF;
END PROCESS im_mem;
END archincomplete;
 Note: the incomplete specification of the IF...THEN...
statement causes a latch to be synthesized to store the
previous state of ‘c’
Implicit memory:
Example of complete specification
ARCHITECTURE archcomplete OF
complete IS
BEGIN
no_mem: PROCESS (a, b)
BEGIN
IF a = '1'
THEN c <= b;
ELSE c <= '0';
END IF;
END PROCESS no_mem;
END archcomplete;
a
b
 The conditional statement is fully specified, and this
causes the process to synthesize to a single gate
c
The rules to avoid implicit memory
 To avoid the generation of unexpected latches
 always terminate an IF...THEN... statement with an
ELSE clause
 cover all alternatives in a CASE statement
• define every alternative individually, or
• terminate the CASE statement with a WHEN
OTHERS... clause, e.g.,
CASE coin_inserted IS
WHEN quarter =>
WHEN dime =>
WHEN nickel =>
WHEN OTHERS =>
END CASE;
total<=total+25;
total<=total+10;
total<=total+5;
total<=total;
error<=‘1’;
Exercise #4
 Making use of the previous examples, write an
entity/architecture pair for the following design:
ENC
COUNTER
DATA
LD
4
DIN
LD
COUNT
Q
4
ENC
COMPARATOR
CLOCK
P
RST
RESET (sync)
P=Q
Q
REGISTER
DIN
ENR
Q
ENR
4
Exercise #4: Instructions
 Create a new project using the Project Wizard
 Choose <file>, <new>, <Project - Target Device>
 Name your project exercise4, click <Next>
 Select the file ex4.vhd and <Add> it to the project
 The target device is 32 Macrocell 8.5 ns CPLD in a 44 pin
TQFP package. Choose CY7C371I-143AC
 Modify the code in the editor window on the right to perform the
function shown in the prior diagram.
 Hints:
 Use 2 processes and a concurrent statement
 Use the register, counter, and comparator shown previously
 Incorporate count enable logic in count process
Exercise #4: Instructions (contd.)
 To simulate your design with the Aldec Simulator, open the
VHDL file C:\warp\class\vhd\ex4.vhd and then select
<Simulation> <Initialize Simulation>
 Add all of the signals by selecting <Waveform> <Add
Signals> (or using the shortcut
). When the window
opens, double click on each signal in the right hand box until
all signals are added.
 Enter the stimulus found on the following page, reference the
applications note handed out in class for additional details
Exercise #4: Instructions (contd.)
 Add the following stimulus:
 reset <= formula 1 0, 0 20 ns, 1 300 ns
 clock <= clock of 100 MHz
 enr <= formula 0 0, 1 70 ns, 0 80 ns
 ld <= formula 0 0, 1 120 ns, 0 130 ns
 data <= 0000 0, 1100 50 ns, 16#3 100 ns, 16#0 150 ns
 enc <= formula 0 0, 1 160 ns
 After completing your design, back annotate the pin numbers
by choosing <Project> <Annotate> and then <OK>. To view
the back annotated pins, select <View> <Control File> from
the pull down menu’s
Exercise #4: Additional Help
 To get help on the format for adding stimulators (or any other
topic), open up the stimulator dialog box and click on the
question mark in the upper right corner ( ) then in the Enter
Formula box.
Exercise #4: Aldec Simulator Waveform
Exercise #4: Solution
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY ex4 IS PORT (
clock, reset, enc, enr, ld: IN std_logic;
data:
IN std_logic_vector (3 DOWNTO 0);
count:
BUFFER std_logic_vector(3 DOWNTO 0));
END ex4;
USE WORK.std_arith.ALL; -- for counter and Ultragen
ARCHITECTURE archex4 OF ex4 IS
SIGNAL comp: std_logic;
SIGNAL regout: std_logic_vector (3 DOWNTO 0);
BEGIN
reg: PROCESS (clock)
BEGIN
IF RISING_EDGE(clock)
THEN
IF enr = '1' THEN
regout <= data;
END IF;
END IF;
END PROCESS reg;
Exercise #4: Solution (contd.)
cntr: PROCESS (clock)
BEGIN
IF RISING_EDGE(clock) THEN
IF reset = '1'
THEN count <= "0000";
ELSIF ld = '1'
THEN count <= data;
ELSIF enc = '1' AND comp = '0'
THEN count <= count + 1;
END IF;
END IF;
END PROCESS cntr;
comp <= '1' WHEN regout = count ELSE '0';
END archex4;
Exercise #4: Control File
Ex4.ctl:
Attribute
Attribute
Attribute
Attribute
Attribute
Attribute
Attribute
Attribute
Attribute
Attribute
Attribute
Attribute
Attribute
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
PIN_NUMBERS
of
of
of
of
of
of
of
of
of
of
of
of
of
count(1) is "37" ;
count(2) is "30" ;
data(2) is "29" ;
data(1) is "27" ;
data(0) is "26" ;
count(3) is "25" ;
count(0) is "18" ;
data(3) is "15" ;
ld is "14" ;
enc is "13" ;
reset is "12" ;
clock is "7" ;
enr is "4" ;
State machines
 Moore Machines
 A finite state machine in which the outputs
change due to a change of state
 Mealy Machines
 A finite state machine in which the outputs can
change asynchronously i.e., an input can cause
an output to change immediately
Moore machines
 Outputs may change only with a change of state
 Multiple implementations include:
 Arbitrary state assignment
• outputs must be decoded from the state bits
• combinatorial decode
• registered decode
 Specific state assignment
• outputs may be encoded within the state bits
• one-hot encoding
Example: A Traffic Light Controller
 Let’s take a look at an example state machine and see
how to describe it using the 3 types of
implementations:
TIMER2
TIMER3
RESET
(asynchronous)
TIMER1
TIMER2
RED
GREEN
R='1'
G='1'
YELLOW
TIMER1
TIMER3
Y='1'
Moore state machine implementations (1)
 Outputs decoded from state bits COMBINATORIALLY
 combinatorial output logic is in series with state registers
 outputs are a function of the present state only
 time from clock to output (tco) is long
Present State
Inputs
Next
State
Logic
Next State
Output
Logic
State
Registers
Tco + tpd
Outputs
Example: The Entity Declaration
 The entity declaration remains exactly the same for each
implementation.
 For example:
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY state_machine IS PORT (
clock, reset:
timer1, timer2, timer3:
r, y, g:
END state_machine;
IN std_logic;
IN std_logic;
OUT std_logic);
Example: Solution 1
 Combinatorial outputs decoded from the state registers
ARCHITECTURE arch_1 OF state_machine IS
TYPE traffic_states IS (red, yellow, green); -- enumerated type
SIGNAL sm: traffic_states;
BEGIN
fsm: PROCESS (clock, reset) -- the process describes the
BEGIN
-- state machine only
IF reset = '1' THEN
sm <= red;
ELSIF rising_edge(clock) THEN
CASE sm IS
WHEN red => IF timer1=‘1’
THEN sm <= green;
ELSE sm <= red;
END IF;
WHEN green => IF timer2=’1'
THEN sm <= yellow;
ELSE sm <= green;
END IF;
Example: Solution 1 (contd.)
WHEN yellow =>
IF timer3=’1’
THEN sm <= red;
ELSE sm <= yellow;
END IF;
WHEN others => sm <= red;
END CASE;
END IF;
END PROCESS fsm;
-- the outputs are decoded from the state machine
-- registers using combinatorial logic
r <= '1' WHEN (sm = red) ELSE '0';
g <= '1' WHEN (sm = green) ELSE '0';
y <= '1' WHEN (sm = yellow) ELSE '0';
END arch_1;
Moore state machine implementations (2)
 Outputs decoded from state bits using REGISTERS
 registered output logic is in parallel with state registers
 outputs are a function of the previous state and the inputs
 tco is shorter, but you need more registers
Inputs
Next
State
Logic
State
Registers
Output
Logic
Output
Registers
tco
Present State
Outputs
Example: Solution 2
 Registered outputs decoded from the state registers
ARCHITECTURE arch_2 OF state_machine IS
TYPE traffic_states IS (red, yellow, green);
SIGNAL sm: traffic_states;
BEGIN
fsm: PROCESS (clock, reset) -- the process describes the
BEGIN
-- state machine AND the outputs
IF reset = '1' THEN
sm <= red;
r<=‘1’; g<=‘0’; y<=‘0’;
ELSIF rising_edge(clock) THEN
CASE sm IS
WHEN red => IF timer1=‘1’
THEN sm <= green;
r<=‘0’; g<=‘1’; y=‘0’;
ELSE sm <= red;
r<=‘1’; g<=‘0’; y=‘0’;
END IF;
Example: Solution 2 (contd.)
WHEN green =>
IF timer2=’1'
THEN sm <= yellow;
r<=‘0’; g<=‘0’; y<=‘1’;
ELSE sm <= green;
r<=‘0’; g<=‘1’; y<=‘0’;
END IF;
WHEN yellow => IF timer3=’1'
THEN sm <= red;
r<=‘1’; g<=‘0’; y<=‘0’;
ELSE sm <= yellow;
r<=‘0’; g<=‘0’; y<=‘1’;
END IF;
WHEN others => sm <= red;
END CASE;
END IF;
END PROCESS fsm;
END arch_2;
Moore State Machine Implementations (3)
 We encoded the outputs within the state registers
State
Red
Green
Yellow
State Encoding
S0
1
0
0
100
S1
0
1
0
010
S2
0
0
1
001
Note: Both bits of the state encoding are used as outputs
Inputs
Logic
State
Registers
Tco
Outputs
Example: Solution 3
 Outputs encoded inside the state registers
ARCHITECTURE arch_3 OF state_machine IS
SIGNAL
CONSTANT
CONSTANT
CONSTANT
sm:
red:
green:
yellow:
std_logic_vector(2
std_logic_vector(2
std_logic_vector(2
std_logic_vector(2
DOWNTO
DOWNTO
DOWNTO
DOWNTO
0)
0)
0)
0)
;
:= ”100" ;
:= "010" ;
:= "001" ;
BEGIN
fsm: PROCESS (clock, reset) -- the process describes the
BEGIN
-- state machine only
IF reset = '1' THEN
sm <= red;
ELSIF rising_edge(clock) THEN
CASE sm IS
WHEN red => IF timer1=‘1’
THEN sm <= green;
ELSE sm <= red;
END IF;
Example: Solution 3 (contd.)
WHEN green =>
IF timer2=’1'
THEN sm <= yellow;
ELSE sm <= green;
END IF;
WHEN yellow => IF timer3=’1’
THEN sm <= red;
ELSE sm <= yellow;
END IF;
WHEN others => sm <= red;
END CASE;
END IF;
END PROCESS fsm;
r <= sm(2);
g <= sm(1);
y <= sm(0);
END arch_3;
-- the outputs are just taken from
-- the state machine registers
-- (no decode logic required)
State Machines: One-hot Encoding
 One state per flip-flop
 in FPGA-type architectures
• reduces the next state logic
• requires fewer levels of logic cells
• enables high-speed state machines (> 100MHz)
 in CPLDs
• reduces the number of product terms
• can eliminate ‘expander’ product terms (i.e.
reduce delays, and increase operating speed)
• but, uses more macrocells
Example: One-hot-one Solution
 Combinatorial outputs decoded from the state registers
ARCHITECTURE arch_1 OF state_machine IS
TYPE traffic_states IS (red, yellow, green); -- enumerated type
SIGNAL sm: traffic_states;
ATTRIBUTE state_encoding OF traffic_states: TYPE IS one_hot_one;
BEGIN
fsm: PROCESS (clock, reset) -- the process describes the
BEGIN
-- state machine only
IF reset = '1' THEN
sm <= red;
ELSIF rising_edge(clock) THEN
CASE sm IS
WHEN red => IF timer1=‘1’
THEN sm <= green;
ELSE sm <= red;
END IF;
WHEN green => IF timer2=’1'
THEN sm <= yellow;
ELSE sm <= green;
END IF;
Example: One-hot-one Solution (contd.)
WHEN yellow => IF timer3=’1'
THEN sm <= red;
ELSE sm <= yellow;
END IF;
WHEN others => sm <= red;
END CASE;
END IF;
END PROCESS fsm;
-- the outputs are decoded from the state machine
-- registers using combinatorial logic
r <= '1' WHEN (sm = red) ELSE '0';
g <= '1' WHEN (sm = green) ELSE '0';
y <= '1' WHEN (sm = yellow) ELSE '0';
END arch_1;
State Machine Encoding: Example
State Sequential
S0
000
S1
001
S2
010
S3
011
S4
100
S5
101
One-hot-one
000001
000010
000100
001000
010000
100000
 S3 State Logic
 Sequential - enable * /b2 * b1 * b0
 One-hot-one - enable * b3
Moore Machines: Summary
 Outputs decoded from the state bits
• flexibility during the design process
• using enumerated types allows automatic
state assignment during compilation
 Outputs encoded within the state bits
• manual state assignment using constants
• the state registers and the outputs are merged
• reduces the number of registers
• but, may require more product terms
 One-Hot encoding
• reduces next state decode logic
• high speed operation
• but, uses more registers
Mealy Machines
 Outputs may change with a change of state OR with
a change of inputs
 Mealy outputs are non-registered because they
are functions of the present inputs
State
Registers
Inputs
Logic
Outputs
Example: The Wait State Generator
 State diagram:
PWAIT
RESET
(async)
REQ
IDLE
RETRY
RETRY_OUT='1'
if, ENABLE='0'
REQ
PWAIT
Example: Mealy Machine Solution
ARCHITECTURE archmealy1 OF mealy1 IS
TYPE fsm_states IS (idle, retry);
SIGNAL wait_gen: fsm_states;
BEGIN
fsm: PROCESS (clock, reset)
BEGIN
IF reset = '1' THEN
wait_gen <= idle;
ELSIF FALLING_EDGE(clock) THEN
CASE wait_gen IS
WHEN idle
=> IF req = '0'
THEN wait_gen <= retry;
ELSE wait_gen <= idle;
END IF;
WHEN retry => IF pwait = '1' THEN wait_gen <= idle;
ELSE wait_gen <= retry;
END IF;
WHEN OTHERS => wait_gen <= idle;
END CASE;
END IF;
END PROCESS fsm;
retry_out <= '1' WHEN (wait_gen = retry AND enable='0') ELSE '0';
END archmealy1;
Exercise #5
 Design a state machine to implement the function
shown below:
RESET
(sync)
POS
hold
POS
sample
extend
clear='0'
track='1'
track='1'
Exercise #5: Instructions
 Using the Project Wizard create a new project named exercise5
and add the template ex5.vhd
 The target device is 32 Macrocell 10 ns CPLD in a 44 pin PLCC
package. Choose CY7C371I-110JC
 Use automatic state bit assignment using an enumerated type
 Compile and synthesize your design using Warp
 Check the report file for the number of macrocells used.
 What is the clock-to-output time (tco)?
 Change your state machine to use constants as follows:
 hold=“10” sample=“01” extend=“11”
 Re-compile your design and check the report file again
 How many macrocells are utilized now ? What is the tco?
Exercise #5: Instructions (contd.)
 To simulate your design with the Aldec Simulator, open the
VHDL file C:\warp\class\vhd\ex5.vhd and then select
<Simulation> <Initialize Simulation>
 Add all of the signals by selecting <Waveform> <Add
Signals> (or using the shortcut
). When the window
opens, double click on each signal in the right hand box until
all signals are added.
 Select the ‘clock’ signal with the <left mouse> button. Now
depress the <right mouse> button and select <Stimulators>.
Choose <Clock> from the stimulator type pull down menu, set
the frequency to 50MHz and then depress <apply>.
Exercise #5: Instructions (contd.)
 Select the ‘reset’ signal with the <left mouse> button. Now
choose <Waveform> <Edit Mode> (or using the shortcut
).
Move the mouse pointer to <0ns> then hold down the <left
mouse> button and drag to the <300ns> mark (section will
highlight). Depress the <1> key. Select <50ns> to <250ns>
and depress the <0> key. Select the ‘reset’ signal with the <left
mouse> button. Now depress the <right mouse> button and
select <Stimulators>. Choose <Custom> from the stimulator
type pull down menu, then depress <apply>.
 Repeat the above for the ‘pos’ signal, making it high from
<0ns> to <100ns>, low from <100ns> to <120ns> then high
from <120ns> to <300ns>. Remember to set to <Custom>
 Run the simulator for 300ns
Exercise #5: Instructions (contd.)
 If you are having a problem drawing waveforms, assure that
the simulator is not running. To stop the simulation, choose
<End Simulation> from the <Simulation> pull down menu.
 If you are having problems saving the waveforms that you
have drawn in by hand, assure that the the letters ‘Cs’ are in
the stimulator column of the waveform view. If a ‘Cs’ is not
displayed it is because the <Apply> button was not depressed
after setting the signal to a <Custom> stimulator type.
 After loading a new waveform it is best to reset the simulator
by choosing <Initialize Simulator> from the <Simulation>
pull down menu.
 Verify that your waveform is similar to the view on the
following page.
Exercise #5: Aldec Simulator Waveform
Exercise #5: Solution A
Using an Enumerated Type
Macrocells = 3, Tco2 (Tco + Tpd) = 10.5ns
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY ex5 IS PORT (
clock, pos,
reset:
IN std_logic;
clear, track:
OUT std_logic);
END ex5;
ARCHITECTURE archex5 OF ex5 IS
TYPE states IS (hold, sample, extend);
SIGNAL fsm: states;
BEGIN
clear <= '0' WHEN fsm=sample ELSE '1';
track <= '1' WHEN (fsm=extend or fsm=sample) ELSE '0';
Exercise #5: Solution A (contd.)
sync: PROCESS (clock)
BEGIN
IF rising_edge(clock) THEN
IF reset = '1' THEN
-- synchronous reset
fsm <= hold;
ELSE
CASE fsm IS
WHEN hold =>
IF pos = '0'
THEN fsm <= sample;
ELSE fsm <= hold;
END IF;
WHEN sample => fsm <= extend;
WHEN extend => fsm <= hold;
WHEN OTHERS => fsm <= hold;
END CASE;
END IF;
END IF;
END PROCESS sync;
END archex5;
Exercise #5: Solution B
Using Constants - Macrocells = 2, Tco = 6.0ns
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY ex5 IS PORT (
clock, pos,
reset:
IN std_logic;
clear, track:
OUT std_logic);
END ex5;
ARCHITECTURE
SIGNAL
CONSTANT
CONSTANT
CONSTANT
BEGIN
clear <=
track <=
archex5 OF ex5 IS
fsm
: std_logic_vector(1
hold
: std_logic_vector(1
sample : std_logic_vector(1
extend : std_logic_vector(1
fsm(1);
fsm(0);
downto
downto
downto
downto
0);
0) := “10”;
0) := “01”;
0) := “11”;
Exercise #5: Solution B (contd.)
sync: PROCESS (clock)
BEGIN
IF rising_edge(clock) THEN
IF reset = '1' THEN
-- synchronous reset
fsm <= hold;
ELSE
CASE fsm IS
WHEN hold =>
IF pos = '0'
THEN fsm <= sample;
ELSE fsm <= hold;
END IF;
WHEN sample => fsm <= extend;
WHEN extend => fsm <= hold;
WHEN OTHERS => fsm <= hold;
END CASE;
END IF;
END IF;
END PROCESS sync;
END archex5;
Hierarchical (Modular) Designs
 A hierarchical design is one which is broken down
into many levels, with a top level design bringing all
the lower-level components together
 This allows very complex designs to be divided
down into smaller, more easily managed modules
 In the past, this was the major advantage of
schematic capture tools
 But, VHDL also supports hierarchical designs !!
Hierarchical Design Methodology
 Advantages:
 Components (VHDL models) can be created, tested
and stored for later use
 Allows the re-use of common building blocks
 Allows you to purchase 3rd Party off-the-shelf
modules (e.g. UART, PCIbus Interface etc)
 Makes the design more readable and easier to
understand
 Complex design tasks can be split across many
designers in a team
VHDL Hierarchy Decomposition
 In VHDL, hierarchy is composed of:
 COMPONENTs
• entity/architecture pairs which can be
instantiated (placed) within other designs
 PACKAGEs
• a collection of one or more COMPONENTs
and other declarations
 LIBRARIES
• a collection of COMPILED design units
• e.g. packages, components, entity/architecture
pairs etc.
Packages: How it all fits together
mux2to1
p
q
a
c
a
i
r
b
c
t
b
sel
s
sel
•
•
schematic
entity/architecture
toplevel
mux2to1
•
•
mux2to1
a
•
•
c
b
sel
•
•
symbol
component
library
package
schematic
entity/architecture
Hierarchy Management
 Libraries are used to store re-usable components, type definitions,
overloaded operators etc. You add the ‘LIBRARY’ and ‘USE’
clauses to your code to get access to them
Your Design (VHDL)
LIBRARY ieee;
USE ieee.std_logic_1164..
USE work.std_arith.all
Library (Compiled) Packages (VHDL)
ieee
std_logic_1164
Library (Compiled) Packages (VHDL)
work
std_arith
Others (VHDL)
std_logic
type
definitions
Others (VHDL)
overloaded
operators
Package and Component Declarations
 When you have created a working entity/architecture
pair, you need to add a component declaration to
make it a re-usable COMPONENT
 COMPONENTS need to be stored in PACKAGES,
so you need to write a package declaration to store
all your components
 When you compile your package with no errors, the
components will be stored in the WORK library
 WORK is the default library where everything YOU
compile gets stored. Because it is the default library,
you do NOT need to add:
LIBRARY WORK; -- not required
Package and Component
Declarations: An Example
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
PACKAGE mymuxpkg IS
COMPONENT mux2to1 PORT (
a, b, sel: IN std_logic;
c:
OUT std_logic);
END COMPONENT;
END mymuxpkg;
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY mux2to1 IS PORT (
a, b, sel: IN std_logic;
c:
OUT std_logic);
END mux2to1;
ARCHITECTURE archmux2to1 OF mux2to1 IS
BEGIN
c <= (a AND NOT sel) OR (b AND sel);
END archmux2to1;
Package and Component
Declaration File
(VHDL)
Entity/Architecture
File (VHDL)
Hierarchical design: Example
 Signals are connected via a PORT MAP that associates signals with the
component's I/O
 Port map association can be either explicit (named) or implicit (positional)
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY toplevel IS PORT (
s:
IN std_logic;
p, q, r: IN std_logic_vector(2 DOWNTO 0);
t:
OUT std_logic_vector(2 DOWNTO 0));
END toplevel;
USE WORK.mymuxpkg.ALL;
ARCHITECTURE arch_top_level OF toplevel IS
SIGNAL i: std_logic_vector(2 DOWNTO 0);
Named Association
BEGIN
m0: mux2to1 PORT MAP (a=>i(2), b=>r(0), sel=>s, c=>t(0));
m1: mux2to1 PORT MAP (c=>t(1), b=>r(1), a=>i(1), sel=>s);
m2: mux2to1 PORT MAP (i(0), r(2), s, t(2));
i <= p AND NOT q;
Positional Association
END arch_top_level;
Schematic of example
mux2to1
a
i(2)
t(0)
i(1)
mux2to1
a
m0 c
b
r(0)
sel
s
mux2to1
t(1)
i(0)
a
m1 c
r(1)
b
sel
m2 c
r(2)
b
sel
t(2)
Exercise #6
 Making use of exercise #4, we will use a separate
entity/architecture for each block and use VHDL hierarchy
ENC
COUNTER
DATA
LD
4
DIN
LD
COUNT
Q
4
ENC
COMPARATOR
CLOCK
P
RST
RESET (sync)
P=Q
Q
REGISTER
DIN
ENR
Q
ENR
4
Exercise #6 : Instructions
 Write a hierarchical VHDL description of the previous
schematic which instantiates all of the components shown in
the design
 The entity/architecture is given for all 3 components
• count4.vhd, reg4.vhd, comp4.vhd
 Complete the package which has the component
declarations for all 3 components
• package.vhd
 Complete the top level file which instantiates the 3
components and makes the interconnections
• ex6.vhd
Exercise #6: Instructions
 Using the Project Wizard create a new project named exercise6
and add the templates count4.vhd, reg4.vhd, comp4.vhd,
package.vhd and ex6.vhd in THE ORDER shown
 The target device is 256 Macrocell 7.5 ns CPLD in a 160 pin
TQFP package. Choose CY7C37256P160-154AC
 Highlight the top-level (lowermost) file (ex6.vhd) and Click-on
the Set top button
 Highlight the top 3 files (one at a time) and Click-on the Compile
selected button
 Before compiling package.vhd and ex6.vhd, you must complete
the files.
 Once all of the files have been compiled separately, use the
Compile Project
button for subsequent compiles
Exercise 6 Solution: package.vhd
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
PACKAGE ex6_pkg IS
COMPONENT comp4 PORT (
p, q : IN std_logic_vector (3 DOWNTO 0);
peqq : OUT std_logic);
END COMPONENT;
COMPONENT reg4 PORT (
clk, enr : IN std_logic;
din
: IN std_logic_vector(3 DOWNTO 0);
q
: OUT std_logic_vector(3 DOWNTO 0));
END COMPONENT;
Exercise 6 Solution: package.vhd (cont)
COMPONENT count4 PORT(
clk, enc, ld, rst : IN
std_logic;
din
: IN
std_logic_vector(3 downto 0);
q
: BUFFER std_logic_vector(3 downto 0));
END COMPONENT;
END ex6_pkg;
Exercise 6 Solution: Top Level File - ex6.vhd
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY ex6 IS PORT (
load, clock, reset
enr, enc
data
count
END ex6;
:
:
:
:
USE work.ex6_pkg.ALL;
ARCHITECTURE ex6_arch OF ex6 IS
IN
IN
IN
BUFFER
std_logic;
std_logic;
std_logic_vector(3 downto 0);
std_logic_vector(3 downto 0));
-- get access to your components
SIGNAL regout
: std_logic_vector(3 downto 0);
SIGNAL peqq
: std_logic;
SIGNAL not_peqq : std_logic;
-- internal bus
-- internal net
-- internal net
Exercise 6 Solution :Top Level File - ex6.vhd
BEGIN
U1: count4 PORT MAP (din=>data, ld=>load, enc=>not_peqq,
clk=>clock, rst=>reset, q=>count);
U2: reg4 PORT MAP (din=>data, enr=>enr, clk=>clock,
q=>regout);
U3: comp4 PORT MAP (p=>count, q=>regout, peqq=>peqq);
not_peqq <= enc AND NOT(peqq);
END ex6_arch;
-- create the inverter
Exercise 6: Summary
 We created entity/architectures for each component. We stored those
components in a package so that we could RE-USE them
We included ALL “components” in the “ex6_pkg” package which was
compiled into the “work” library
Your Design (VHDL)
LIBRARY ieee;
USE ieee.std_logic_1164..
USE work.ex6_pkg.all
Library (Compiled) Packages (VHDL)
ieee
std_logic_1164
Library (Compiled) Packages (VHDL)
work
ex6_pkg.vhd
count4
reg4
comp4
Others (VHDL)
std_logic
type
definitions
Components(VHDL)
count4.vhd
reg4.vhd
comp4.vhd
Creating repetitive structures
 e.g., a 32-bit serial to parallel converter:
reset
si
q(31)
q(30)
q(29)
•••
q(1)
q(0)
po(1)
po(0)
clock
po(31)
po(30)
po(29)
The GENERATE statement
 Used to specify repetitive or conditional execution of
a set of concurrent statements
 Useful for instantiating arrays of components
USE WORK.rtlpkg.ALL; -- User-defined package containing dsrff
ENTITY sipo IS PORT (
clk, reset: IN std_logic;
si:
IN std_logic;
po:
BUFFER std_logic_vector(31 DOWNTO 0));
END sipo;
ARCHITECTURE arch_sipo OF sipo IS
SIGNAL p_temp: std_logic_vector(31 DOWNTO 0);
SIGNAL zero: std_logic := ‘0’;
BEGIN
gen: FOR i IN 0 TO 30 GENERATE
nxt: dsrff PORT MAP (p_temp(i+1), zero, reset, clk, p_temp(i));
END GENERATE;
beg: dsrff PORT MAP (si, zero, reset, clk, p_temp(31));
po <= p_temp;
END arch_sipo;
Multiplexing I/O pins:
LIBRARY ieee ;
USE ieee.std_logic_1164.ALL;
USE WORK.std_arith.all ;
ENTITY ldcnt IS PORT (
clk, ld, oe: IN std_logic;
count:
INOUT std_logic_vector(7 DOWNTO 0));
END ldcnt;
ARCHITECTURE archldcnt OF ldcnt IS
SIGNAL int_count: std_logic_vector(7 DOWNTO 0);
BEGIN
cnt: PROCESS (clk)
BEGIN
IF RISING_EDGE(clock) THEN
IF ld = '1' THEN int_count <= count; -- count as "IN"
ELSE int_count <= int_count + 1;
END IF;
END IF;
END PROCESS cnt ;
outen: PROCESS (oe, int_count) BEGIN
IF oe = '1’ THEN count <= int_count ; -- count as "OUT"
ELSE count <= (OTHERS => 'Z') ;-- count as "OUT"
END IF ;
-- equivalent to count <= "ZZZZZZZZ"
END PROCESS outen;
END archldcnt;
Exercise #7
 Design a Moore Machine to implement the Output Enable
Controller shown below:
68040
DRAM BANK A
DRAM BANK C
Output
Enable
Controller
DRAM BANK B
DRAM BANK D
DRAM
Controller
Exercise #7: The FSM chart
 Use the following FSM chart:
RESET
RAM
IDLE
OE=1111
/RAM
CHOOSE
OE=1111
/EOC
/A3 AND /A2
BANK A
OE=1110
/A3 AND A2
EOC
BANK B
OE=1101
A3 AND /A2
EOC
A3 AND A2
BANK C
EOC
OE=1011
BANK D
OE=0111
EOC
Exercise #7: Instructions





The target device is a CY7C371I-143JC
Use a synchronous reset
Decode the outputs in parallel with the next state
Compile and synthesize your design using Warp
Determine the maximum frequency of operation
using the report file
Exercise #7: Solution
ENTITY ex7 IS PORT (
clk, reset: IN std_logic;
ram, eoc:
IN std_logic;
a3a2:
IN std_logic_vector(1 DOWNTO 0) ;
oe:
OUT std_logic_vector(3 DOWNTO 0));
END ex7;
ARCHITECTURE archex7 OF ex7 IS
TYPE oe_states IS (idle, choose, banka, bankb, bankc, bankd);
ATTRIBUTE state_encoding OF oe_states : TYPE IS gray ;
SIGNAL present_state, next_state : oe_states ;
SIGNAL oe_out : std_logic_vector(3 DOWNTO 0) ;
BEGIN
Exercise #7: Solution (contd.)
fsm: PROCESS (clk)
BEGIN
IF RISING_EDGE(clock) THEN
IF reset = '1' THEN
next_state <= idle;
ELSE
CASE present_state IS
WHEN idle => IF ram = '0'
THEN next_state <= choose ;
ELSE next_state <= idle ;
END IF ;
WHEN choose =>
CASE a3a2 IS
WHEN "00" => next_state <= banka ;
WHEN "01" => next_state <= bankb ;
WHEN "10" => next_state <= bankc ;
WHEN "11" => next_state <= bankd ;
WHEN OTHERS => next_state <= banka ;
END CASE ;
WHEN banka => IF eoc = '1'
THEN next_state <= bankb ;
ELSE next_state <= idle ;
END IF ;
Exercise #7: Solution (contd.)
WHEN bankb => IF eoc = '1'
THEN next_state <=
ELSE next_state <=
END IF ;
WHEN bankc => IF eoc = '1'
THEN next_state <=
ELSE next_state <=
END IF ;
WHEN bankd => IF eoc = '1'
THEN next_state <=
ELSE next_state <=
END IF ;
WHEN OTHERS => next_state <= idle;
END CASE;
END IF ;
END IF;
END PROCESS fsm;
bankc ;
idle ;
bankd ;
idle ;
banka ;
idle ;
Exercise #7: Solution (contd).
output_logic: PROCESS (next_state)
BEGIN
CASE next_state IS
WHEN idle => oe_out <= "1111" ;
WHEN choose => oe_out <= "1111" ;
WHEN banka => oe_out <= "1110" ;
WHEN bankb => oe_out <= "1101" ;
WHEN bankc => oe_out <= "1011" ;
WHEN bankd => oe_out <= "0111" ;
WHEN OTHERS => oe_out <= "1111" ;
END CASE;
END PROCESS output_logic ;
advance_state: PROCESS (clk)
BEGIN
IF RISING_EDGE(clock)
THEN present_state <= next_state ;
oe <= oe_out ;
END IF;
END PROCESS ;
END archex7;
VHDL User-defined Attributes
 VHDL construct which is used to provide information
about VHDL objects such as entities, architectures,
types, and signals.
 Warp user-defined attributes are used as synthesis
directives to the compiler. These include:
• state_encoding
• enum_encoding
• pin_numbers
• synthesis_off
The state_encoding attribute
 This is used to specify the state encoding scheme of the FSMs
in a VHDL file.
 The default scheme for CPLDs is sequential.
 Other schemes such as one_hot_one, one_hot_zero and gray
encodings are available.
TYPE state_type IS (idle,state1,state2,state3);
ATTRIBUTE state_encoding OF state_type: TYPE IS sequential;
The enum_encoding Attribute
 Used to specify the exact internal encoding to be use for
each value of a user-defined enumerated type.
 Overrides state_encoding in same description.
TYPE states IS (idle,state1,state2,state3);
ATTRIBUTE enum_encoding OF states: TYPE IS "11 01 00 10";
The pin_numbers attribute
 Used to map the external signals of an entity to the
pins on the target device
 Allows the back-annotation of pin placements
after synthesis, e.g.,
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY counter IS PORT (
clock, reset: IN std_logic;
count:
OUT std_logic_vector(3 DOWNTO 0)
);
ATTRIBUTE pin_numbers OF counter:ENTITY IS
"clock:13 reset:2" &
" count(3):3 count(2):4 count(1):5 count(0):6";
END counter;
The synthesis_off attribute
 Controls the flattening and factoring of signals
 Makes the signal a factoring point
 Useful when a signal with a large number of product
terms is used in other equations
 Helpful in cases where substitution causes
unacceptable compile time (due to exponentially
increasing CPU and memory requirements)
 Achieves more efficient implementation
 Should only be used on combinatorial equations
 Registered equations are natural factoring points
synthesis_off: CPLD Example
 An 8-bit comparator controlling a 4-bit, 2-to-1
multiplexer
c(7 DOWNTO 0)
d(7 DOWNTO 0)
8-bit
compare
a(3 DOWNTO 0)
b(3 DOWNTO 0)
mux
x(3 DOWNTO 0)
Without synthesis_off
 An implementation (without synthesis_off)
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY mux IS PORT (
a, b: IN std_logic_vector(3 DOWNTO 0);
c, d: IN std_logic_vector(7 DOWNTO 0);
x:
OUT std_logic_vector(3 DOWNTO 0));
END mux;
ARCHITECTURE archmux OF mux IS
BEGIN
x <= a WHEN (c = d) ELSE b;
END archmux;
 Resources used: 1092 product terms, 68 sum splits,
72 macrocells - the comparison is not done on a bit
by bit basis
Comparison: with a 4-bit vector
S_2
b
+ b
S_1
=
* c_0 * /d_0 + b * /c_3 * d_3 + b * c_3 * /d_3 + b * /c_2 * d_2
* c_2 * /d_2 + b * /c_1 * d_1 + b * c_1 * /d_1 + b * /c_0 * d_0
=
a * c_3 * c_2 * c_1 * /c_0 * d_3 * d_2 * d_1 * /d_0
+ a * /c_3 * c_2 * c_1 * /c_0 * /d_3 * d_2 * d_1 * /d_0
+ a * c_3 * /c_2 * c_1 * /c_0 * d_3 * /d_2 * d_1 * /d_0
+ a * /c_3 * /c_2 * c_1 * /c_0 * /d_3 * /d_2 * d_1 * /d_0
+ a * c_3 * c_2 * /c_1 * /c_0 * d_3 * d_2 * /d_1 * /d_0
+ a * /c_3 * c_2 * /c_1 * /c_0 * /d_3 * d_2 * /d_1 * /d_0
+ a * c_3 * /c_2 * /c_1 * /c_0 * d_3 * /d_2 * /d_1 * /d_0
+ a * /c_3 * /c_2 * /c_1 * /c_0 * /d_3 * /d_2 * /d_1 * /d_0
+ a * c_3 * c_2 * c_1 * c_0 * d_3 * d_2 * d_1 * d_0
+ a * /c_3 * c_2 * c_1 * c_0 * /d_3 * d_2 * d_1 * d_0
+ a * c_3 * /c_2 * c_1 * c_0 * d_3 * /d_2 * d_1 * d_0
+ a * /c_3 * /c_2 * c_1 * c_0 * /d_3 * /d_2 * d_1 * d_0
+ a * c_3 * c_2 * /c_1 * c_0 * d_3 * d_2 * /d_1 * d_0
+ a * /c_3 * c_2 * /c_1 * c_0 * /d_3 * d_2 * /d_1 * d_0
+ a * c_3 * /c_2 * /c_1 * c_0 * d_3 * /d_2 * /d_1 * d_0
+ a * /c_3 * /c_2 * /c_1 * c_0 * /d_3 * /d_2 * /d_1 * d_0
/x0 =
/S_1.CMB * /S_2.CMB
With synthesis_off
 A better implementation (with synthesis_off)
LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
ENTITY mux IS PORT (
a, b: IN std_logic_vector(3 DOWNTO 0);
c, d: IN std_logic_vector(7 DOWNTO 0);
x:
OUT std_logic_vector(3 DOWNTO 0));
END mux;
ARCHITECTURE archmux OF mux
SIGNAL sel: std_logic;
ATTRIBUTE synthesis_off
BEGIN
sel <= '1' WHEN (c = d)
x <= a WHEN (sel = '1')
END archmux;
IS
OF sel:SIGNAL is TRUE;
ELSE '0';
ELSE b;
 Resources used: 24 product terms, 1 partial result, 5
macrocells
Results with synthesis_off
DESIGN EQUATIONS
x_3 = b_3 * /sel.CMB + a_3 * sel.CMB
x_2 = /sel.CMB * b_2 + sel.CMB * a_2
x_1 = /sel.CMB * b_1 + sel.CMB * a_1
x_0 = /sel.CMB * b_0 + sel.CMB * a_0
/sel =
+
+
+
c_0
c_2
c_4
c_6
*
*
*
*
/d_0
/d_2
/d_4
/d_6
+
+
+
+
/c_0
/c_2
/c_4
/c_6
*
*
*
*
d_0
d_2
d_4
d_6
+
+
+
+
c_1
c_3
c_5
c_7
*
*
*
*
/d_1
/d_3
/d_5
/d_7
+
+
+
+
/c_1
/c_3
/c_5
/c_7
*
*
*
*
d_1
d_3
d_5
d_7
CPLD Synthesis Directives
 Some Warp synthesis directives only apply to CPLD
architectures, e.g.,
 Floor planning
• lab_force
• node_num
• pin_avoid
 Product Term distribution
• sum_split
 Speed/Power/Edge rates
• slew_rate
• low_power
The lab_force Attribute
 Forces signals into specific logic blocks in CPLDs
 Should be used sparingly as it restricts the fitter
 First example below forces signal to upper half of
logic block A.
 Second example forces signal to lower half of logic
block B
ATTRIBUTE lab_force OF mysig1: SIGNAL IS A1;
ATTRIBUTE lab_force OF mysig2: SIGNAL IS B2;
The node_num Attribute
 Used to specify internal location for a signal in a CPLD
 Allows signals to be manually allocated to a
specific macrocell location
 May be used to improve product-term allocation
• Example: to assign a signal to the first buried
macrocell in a CY7C372:
ATTRIBUTE node_num OF buried:SIGNAL IS 202;
 More restrictive than lab_force
 Can be used with SPLDs too
The pin_avoid Attribute
 Instructs Warp to leave specified pins unused
 Useful for avoiding ISRTM pins on FLASH370i
devices with dual-function pins
 Could also be used to reserve pins for later use
ATTRIBUTE pin_avoid OF mydesign: ENTITY IS "21 24 26";
The sum_split Attribute
 Sum splitting occurs in FLASH370 when a signal's
equation requires more than 16 product terms
 Two types of sum splitting
 Balanced (default)
• More reliable timing for combinatorial signals
• Uses more macrocells
 Cascaded
ATTRIBUTE sum_split OF mysig:SIGNAL IS balanced ;
ATTRIBUTE sum_split OF mysig:SIGNAL IS cascaded ;
Balanced Sum Splitting
All inputs arrive at same time
Buried Macrocell #1
16 PT’s
S_1
Buried Macrocell #2
6 PT’s
S_2
2 PT’s
PIM
Output = S_1 + S_2
Cascaded Sum Splitting
Other inputs arrive before S_1
If output combinatorial, it may be unstable
Buried Macrocell
16 PT’s
S_1
7 PT’s
6 PT’s
PIM
Output = S_1 + ...
The low_power attribute
 The low power directive can be used to lower the power
consumption in a logic block(s) by 50%. As a result, the logic
block(s) slows down by 5 ns. This directive is valid only for
the Ultra37000 family of CPLDs.
 In VHDL, use the following syntax.
ATTRIBUTE low_power OF entity_name: ENTITY IS “b g e”;
 In Verilog, use the following syntax.
ATTRIBUTE low_power OF module_name: MODULE IS “b g e”;
The slew_rate attribute
 The slew_rate directive can be used to control the output slew
rate of individual pins. This directive is valid only for the
Ultra37000 family of CPLDs.
 Legal values for the slew_rate directive are fast and slow.
 A value of ‘fast’ sets the output slew rate to 3V/ns.
 A value of ‘slow’ sets the output slew rate to 1V/ns.
ATTRIBUTE slew_rate OF sig_name: SIGNAL IS fast;
Warp2/Warp3/Programming
Design
Entry
Schematic
Text/FSM
Front
End
Simulation
Synthesis
Design
Compilation
Fitting
Design
Verification
JEDEC
Sim. Model
JAM file
Simulator
ISR/Impulse3
Back
End
Third Party Tool Support
 CAE Bolt-in Tools
- Viewlogic Workview Plus/Powerview/WorkView Office
- Mentor (CY3144), Cadence (Q4)
 Synthesis Tools
- Synopsys, Exemplar
 PLD Development Tools
- Data I/O Abel 4/5/6 and Synario, CUPL, LOG/iC, OrCAD
 Simulation Tools
- LMG SmartModels
- All VHDL and Verilog Simulators (with timing)
In System Reprogrammability
 ISRTM is the ability to program or reprogram a device after it
has been soldered to the board
 Must be able to retain pin-out and timing to be useful
 CPLD architecture is the key here(Routability/Timing)
 Advantages of ISR
 Reduce device handling
 Ease prototyping
 Enable field upgrades
 Improve manufacturing efficiency
PC Parallel port
ISR connector
Top Three Issues with ISR
#1: Large file sizes
 120KB to 22 MB for a 256-macrocell device
 complicates production
 impractical for field upgrades
#2: No Software Standard
 Beyond JTAG, each approach is different
 Confusing file formats
 Solutions are vendor and platform-specific
#3: Long Programming Times
 Time is money
 Programming can take several minutes on some equipment