algorithmic state machine (asm) charts
DESCRIPTION
ECE 448 Lecture 9. Algorithmic State Machine (ASM) Charts. Required reading. P. Chu, FPGA Prototyping by VHDL Examples Chapter 5, FSM. S. Brown and Z. Vranesic , Fundamentals of Digital Logic with VHDL Design Chapter 8.10, Algorithmic State Machine (ASM) Charts. - PowerPoint PPT PresentationTRANSCRIPT
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George Mason UniversityECE 448 – FPGA and ASIC Design with VHDL
Algorithmic State Machine (ASM) Charts
ECE 448Lecture 9
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2ECE 448 – FPGA and ASIC Design with VHDL
Required reading
• S. Brown and Z. Vranesic, Fundamentals of Digital Logic with VHDL Design
Chapter 8.10, Algorithmic State Machine
(ASM) Charts
• P. Chu, FPGA Prototyping by VHDL Examples
Chapter 5, FSM
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3ECE 448 – FPGA and ASIC Design with VHDL
Algorithmic State Machine (ASM)
Charts
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4ECE 448 – FPGA and ASIC Design with VHDL
Algorithmic State Machine
Algorithmic State Machine –
representation of a Finite State Machine
suitable for FSMs with a larger number of inputs and outputs compared to FSMs expressed using state diagrams and state tables.
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5ECE 448 – FPGA and ASIC Design with VHDL
Elements used in ASM charts (1)
Output signalsor actions
(Moore type)
State name
Condition expression
0 (False) 1 (True)
Conditional outputs or actions (Mealy type)
(a) State box (b) Decision box
(c) Conditional output box
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6ECE 448 – FPGA and ASIC Design with VHDL
State Box• State box – represents a state.• Equivalent to a node in a state diagram or a
row in a state table.• Contains register transfer actions or output
signals• Moore-type outputs are listed inside of
the box. • It is customary to write only the name of the
signal that has to be asserted in the given state, e.g., z instead of z<=1.
• Also, it might be useful to write an action to be taken, e.g., count <= count + 1, and only later translate it to asserting a control signal that causes a given action to take place (e.g., enable signal of a counter).
Output signalsor actions
(Moore type)
State name
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7ECE 448 – FPGA and ASIC Design with VHDL
Decision Box
• Decision box – indicates that a given condition is to be tested and the exit path is to be chosen accordingly
The condition expression may include one or more inputs to the FSM.
Condition expression
0 (False) 1 (True)
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8ECE 448 – FPGA and ASIC Design with VHDL
Conditional Output Box
• Conditional output box
• Denotes output signals that are of the Mealy type.
• The condition that determines whether such outputs are generated is specified in the decision box.
Conditional outputs or actions (Mealy type)
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9ECE 448 – FPGA and ASIC Design with VHDL
ASMs representing simple FSMs
• Algorithmic state machines can model both Mealy and Moore Finite State Machines
• They can also model machines that are of the mixed type
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10ECE 448 – FPGA and ASIC Design with VHDL
Moore FSM – Example 2: State diagram
C z 1 =
Reset
B z 0 = A z 0 = w 0 =
w 1 =
w 1 =
w 0 =
w 0 = w 1 =
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11ECE 448 – FPGA and ASIC Design with VHDL
Present Next state Outputstate w = 0 w = 1 z
A A B 0 B A C 0 C A C 1
Moore FSM – Example 2: State table
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12ECE 448 – FPGA and ASIC Design with VHDL
w
w
w 0 1
0
1
0
1
A
B
C
z
Reset
w
w
w 0 1
0
1
0
1
A
B
C
z
Reset
ASM Chart for Moore FSM – Example 2
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13ECE 448 – FPGA and ASIC Design with VHDL
USE ieee.std_logic_1164.all ;
ENTITY simple ISPORT ( clock : IN STD_LOGIC ;
resetn : IN STD_LOGIC ; w : IN STD_LOGIC ;
z : OUT STD_LOGIC ) ;END simple ;
ARCHITECTURE Behavior OF simple ISTYPE State_type IS (A, B, C) ;SIGNAL y : State_type ;
BEGINPROCESS ( resetn, clock )BEGIN
IF resetn = '0' THENy <= A ;
ELSIF (Clock'EVENT AND Clock = '1') THEN
Example 2: VHDL code (1)
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14ECE 448 – FPGA and ASIC Design with VHDL
CASE y ISWHEN A =>
IF w = '0' THEN y <= A ;
ELSE y <= B ;
END IF ;WHEN B =>
IF w = '0' THENy <= A ;
ELSEy <= C ;
END IF ;WHEN C =>
IF w = '0' THENy <= A ;
ELSEy <= C ;
END IF ;END CASE ;
Example 2: VHDL code (2)
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15ECE 448 – FPGA and ASIC Design with VHDL
Example 2: VHDL code (3)
END IF ;
END PROCESS ;
z <= '1' WHEN y = C ELSE '0' ;
END Behavior ;
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16ECE 448 – FPGA and ASIC Design with VHDL
A
w 0 = z 0 =
w 1 = z 1 = B w 0 = z 0 =
Reset
w 1 = z 0 =
Mealy FSM – Example 3: State diagram
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17ECE 448 – FPGA and ASIC Design with VHDL
ASM Chart for Mealy FSM – Example 3
w
w 0 1
0
1
A
B
Reset
z
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18ECE 448 – FPGA and ASIC Design with VHDL
LIBRARY ieee ;USE ieee.std_logic_1164.all ;
ENTITY Mealy ISPORT ( clock : IN STD_LOGIC ;
resetn : IN STD_LOGIC ; w : IN STD_LOGIC ;
z : OUT STD_LOGIC ) ;END Mealy ;
ARCHITECTURE Behavior OF Mealy ISTYPE State_type IS (A, B) ;SIGNAL y : State_type ;
BEGINPROCESS ( resetn, clock )BEGIN
IF resetn = '0' THENy <= A ;
ELSIF (clock'EVENT AND clock = '1') THEN
Example 3: VHDL code (1)
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19ECE 448 – FPGA and ASIC Design with VHDL
Example 3: VHDL code (2)
CASE y IS WHEN A => IF w = '0' THEN
y <= A ;ELSE
y <= B ;END IF ;
WHEN B =>IF w = '0' THEN
y <= A ;ELSE
y <= B ; END IF ;END CASE ;
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20ECE 448 – FPGA and ASIC Design with VHDL
Example 3: VHDL code (3)
END IF ;
END PROCESS ;
z <= '1' WHEN (y = B) AND (w=‘1’) ELSE '0' ;
END Behavior ;
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21ECE 448 – FPGA and ASIC Design with VHDL
Control Unit Example: Arbiter (1)
Arbiter
reset
r1
r2
r3
g1
g2
g3
clock
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22ECE 448 – FPGA and ASIC Design with VHDL
Idle
000
1xx
Reset
gnt1 g 1 1 =
x1x
gnt2 g 2 1 =
xx1
gnt3 g 3 1 =
0xx 1xx
01x x0x
001 xx0
Control Unit Example: Arbiter (2)
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23ECE 448 – FPGA and ASIC Design with VHDL
Control Unit Example: Arbiter (3)
r 1 r 2
r 1 r 2 r 3
Idle
Reset
gnt1 g 1 1 =
gnt2 g 2 1 =
gnt3 g 3 1 =
r 1 r 1
r 1
r 2
r 3
r 2
r 3
r 1 r 2 r 3
r 1 r 2
r 1 r 2 r 3
Idle
Reset
gnt1 g 1 1 =
gnt2 g 2 1 =
gnt3 g 3 1 =
r 1 r 1
r 1
r 2
r 3
r 2
r 3
r 1 r 2 r 3
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24ECE 448 – FPGA and ASIC Design with VHDL
ASM Chart for Control Unit - Example 4
r 1
r 3 0 1
1
Idle
Reset
r 2
r 1
r 3
r 2
gnt1
gnt2
gnt3
1
1
1
0
0
0
g 1
g 2
g 3
0
0
1
r 1
r 3 0 1
1
Idle
Reset
r 2
r 1
r 3
r 2
gnt1
gnt2
gnt3
1
1
1
0
0
0
g 1
g 2
g 3
0
0
1
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25ECE 448 – FPGA and ASIC Design with VHDL
Example 4: VHDL code (1)
LIBRARY ieee;
USE ieee.std_logic_1164.all;
ENTITY arbiter IS
PORT ( Clock, Resetn : IN STD_LOGIC ;
r : IN STD_LOGIC_VECTOR(1 TO 3) ;
g : OUT STD_LOGIC_VECTOR(1 TO 3) ) ;
END arbiter ;
ARCHITECTURE Behavior OF arbiter IS
TYPE State_type IS (Idle, gnt1, gnt2, gnt3) ;
SIGNAL y : State_type ;
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26ECE 448 – FPGA and ASIC Design with VHDL
Example 4: VHDL code (2)BEGIN
PROCESS ( Resetn, Clock )
BEGIN
IF Resetn = '0' THEN y <= Idle ;
ELSIF (Clock'EVENT AND Clock = '1') THEN
CASE y IS
WHEN Idle =>
IF r(1) = '1' THEN y <= gnt1 ;
ELSIF r(2) = '1' THEN y <= gnt2 ;
ELSIF r(3) = '1' THEN y <= gnt3 ;
ELSE y <= Idle ;
END IF ;
WHEN gnt1 =>
IF r(1) = '1' THEN y <= gnt1 ;
ELSE y <= Idle ;
END IF ;
WHEN gnt2 =>
IF r(2) = '1' THEN y <= gnt2 ;
ELSE y <= Idle ;
END IF ;
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27ECE 448 – FPGA and ASIC Design with VHDL
Example 4: VHDL code (3)
WHEN gnt3 =>
IF r(3) = '1' THEN y <= gnt3 ;
ELSE y <= Idle ;
END IF ;
END CASE ;
END IF ;
END PROCESS ;
g(1) <= '1' WHEN y = gnt1 ELSE '0' ;
g(2) <= '1' WHEN y = gnt2 ELSE '0' ;
g(3) <= '1' WHEN y = gnt3 ELSE '0' ;
END Behavior ;
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RTL Hardware Design by P. Chu
Chapter 10 28
• Incorrect ASM charts: