How can I eliminate "Glitch"?

[Jluis]

Hi everyone!!!! I program a big decoder, so the compilation is ok, but
when I simulated on max plus simulator I got many "glitches". is there
some way to elimante it?? is very important for me to eliminate it,
´cause I use the output sgnals as input signals of other component.

any suggestions
thanks in advance..
JLuis

this is my code.

-- Opcode Decoder (e-mail address removed) March 19th, 2004 José Luis
Fernández Jiménez

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.all;


ENTITY opdecoder IS

PORT( decdataop : IN STD_LOGIC_VECTOR(4 DOWNTO 0);
NOPgp, ADDgp, SUBgp, ADIgp, ANDgp, ORgp, NOTgp, NEGgp, SHLgp,
SHRgp, LDRgp,
STRgp, LDIgp, MOVgp, LDXgp, STXgp, SSPgp, PSHgp, POPgp, JMPgp,
JPLUSgp, JPZgp,
JNEGgp, JNZgp, JZEgp, JSUBgp, RETgp: OUT std_logic
);

END opdecoder;

ARCHITECTURE archopdecoder OF opdecoder IS
SIGNAL temp_op : STD_LOGIC_VECTOR(31 DOWNTO 0);

BEGIN
PROCESS (decdataop)
BEGIN

CASE decdataop IS
WHEN "00000" =>
temp_op <= "00000000000000000000000000000001"; --
NOPgp 0
WHEN "00001" =>
temp_op <= "00000000000000000000000000000010"; --
ADDgp 1
WHEN "00010" =>
temp_op <= "00000000000000000000000000000100"; --
SUBgp 2
WHEN "00011" =>
temp_op <= "00000000000000000000000000001000"; --
ADIgp 3
WHEN "00100" =>
temp_op <= "00000000000000000000000000010000"; --
ANDgp 4
WHEN "00101" =>
temp_op <= "00000000000000000000000000100000"; -- ORgp
5
WHEN "00110" =>
temp_op <= "00000000000000000000000001000000"; --
NOTgp 6
WHEN "00111" =>
temp_op <= "00000000000000000000000010000000"; --
NEGgp 7
WHEN "01000" =>
temp_op <= "00000000000000000000000100000000"; --
SHLgp 8
WHEN "01001" =>
temp_op <= "00000000000000000000001000000000"; --
SHRgp 9
WHEN "01010" =>
temp_op <= "00000000000000000000010000000000"; --
LDRgp 10
WHEN "01011" =>
temp_op <= "00000000000000000000100000000000"; --
STRgp 11
WHEN "01100" =>
temp_op <= "00000000000000000001000000000000"; --
LDIgp 12
WHEN "01101" =>
temp_op <= "00000000000000000010000000000000"; --
MOVgp 13
WHEN "01110" =>
temp_op <= "00000000000000000100000000000000"; --
LDXgp 14
WHEN "01111" =>
temp_op <= "00000000000000001000000000000000"; --
STXgp 15
WHEN "10000" =>
temp_op <= "00000000000000010000000000000000"; --
SSPgp 16
WHEN "10001" =>
temp_op <= "00000000000000100000000000000000"; --
PSHgp 17
WHEN "10010" =>
temp_op <= "00000000000001000000000000000000"; --
POPgp 18
WHEN "10011" =>
temp_op <= "00000000000010000000000000000000"; --
JMPgp 19
WHEN "10100" =>
temp_op <= "00000000000100000000000000000000"; --
JPLUSgp 20
WHEN "10101" =>
temp_op <= "00000000001000000000000000000000"; --
JPZgp 21
WHEN "10110" =>
temp_op <= "00000000010000000000000000000000"; --
JNEGgp 22
WHEN "10111" =>
temp_op <= "00000000100000000000000000000000"; --
JNZgp 23
WHEN "11000" =>
temp_op <= "00000001000000000000000000000000"; --
JZEgp 24
WHEN "11001" =>
temp_op <= "00000010000000000000000000000000"; --
JSUBgp 25
WHEN "11010" =>
temp_op <= "00000100000000000000000000000000"; --
RETgp 26
WHEN OTHERS => NULL;
-- temp_op <= "00000000000000000000000000000000";
END CASE;

END PROCESS;

NOPgp <= temp_op(0);
ADDgp <= temp_op(1);
SUBgp <= temp_op(2);
ADIgp <= temp_op(3);
ANDgp <= temp_op(4);
ORgp <= temp_op(5);
NOTgp <= temp_op(6);
NEGgp <= temp_op(7);
SHLgp <= temp_op(8);
SHRgp <= temp_op(9);
LDRgp <= temp_op(10);
STRgp <= temp_op(11);
LDIgp <= temp_op(12);
MOVgp <= temp_op(13);
LDXgp <= temp_op(14);
STXgp <= temp_op(15);
SSPgp <= temp_op(16);
PSHgp <= temp_op(17);
POPgp <= temp_op(18);
JMPgp <= temp_op(19);
JPLUSgp <= temp_op(20);
JPZgp <= temp_op(21);
JNEGgp <= temp_op(22);
JNZgp <= temp_op(23);
JZEgp <= temp_op(24);
JSUBgp <= temp_op(25);
RETgp <= temp_op(26);

END archopdecoder;

 

[Jim Wu]

Hi everyone!!!! I program a big decoder, so the compilation is ok, but
when I simulated on max plus simulator I got many "glitches". is there
some way to elimante it?? is very important for me to eliminate it,
´cause I use the output sgnals as input signals of other component.

Register the output with a clock.

HTH,
Jim
(e-mail address removed)
http://www.geocities.com/jimwu88/chips

 

[Charles Bailey]

Register the output with a clock.

Yes, I think that is the only way to eliminate the glitches. A
combinational circuit like this is inherently glitchy.

 

[Thomas Stanka]

Hi everyone!!!! I program a big decoder, so the compilation is ok, but
when I simulated on max plus simulator I got many "glitches". is there
some way to elimante it?? is very important for me to eliminate it,
´cause I use the output sgnals as input signals of other component.

You have two possibilities:
1. register the output
2. break your code down to structural code and use technics [1] to
eliminate glitches in digital cirquits.

bye Thomas

[1] In principle all you have to do is to ensure, that there are no
two inputs in a gate that change at the same time while the output of
the gate would change if only one of the two inputs would change but
not if both inputs change their value.

 

[DoesntMatter]

Is this a question on electronics design ? Do you know how you are going
to handle in reality ? Then just model it afer that ...

Or is the question something different ?

Jos De Laender

 

[Ray Andraka]

Not the only way, but perhaps the easiest way.

If the circuit must be combinatorial, you can design the combinatorial
circuit with cover terms to avoid the hazards that result in glitches.
Refer to a basic logic book such as Morris Mano for a detailed discussion on
cover terms and static hazards. The trick then, is to keep your synthesis
tool from optimizing out the cover terms that prevent the static hazards.

Yes, I think that is the only way to eliminate the glitches. A
combinational circuit like this is inherently glitchy.

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email (e-mail address removed)
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759