Variable Subtype Problem

T

Takuon Soho

Guest
I have a 12 bit counter whoose value
needs to be output to 12 output pins
of a cpld
when flag signal goes high (see Process code below).

But I can't figure out how to output my_counter
to a std_logic_vector
because it is a subtype of integer.

I tried things like
bus_0_11 <= std_logic_vector(counter_ty my_counter);
without compilation success.

Anyone know how to do this?

Thanks
Tak

code follows:

entity count12 is port (
clk : in std_logic;
....
bus_0_11: out std_logic_vector(11 downto 0)
);
end count12;


Process(clk,flag)

-- my counter variable declaration
subtype counter_ty is integer range 0 to 4095; -- 12 bit counter,
integer
variable my_counter : counter_ty := 0;

begin

.....

if (flag = '1') then -- flag hi, output count to bus
bus_0_11 <= std_logic_vector(counter_ty my_counter);
flag = '0';
elsif (clk'event and clk = '1') then
my_counter = my_counter + 1;
end if;

end process;
 
Hi ,

Dont use ieee.std_logic_arith.all or ieee.std_lgoci_arith.all for
arithematic operation on std_logic types ......

Package std_logic_arith is developed by SYNOPSYS before the IEEE
packages were available. It should not be used since now that there is
an official IEEE standard. Instead use ieee.numeric_std.all or
ieee.numeric_bit.all for such types arithematic types...

Check this for many other such packages

http://www.eda.org/vhdl-200x/vhdl-200x-ft/packages/files.html

About the code for counter .... he is using flag as a asynchronous
signal to read the data to output port but if at the same time clk
goes high then counter is not incremeted ... I dont think this is what
intended there..

Regards,
Mohammed Khader.
 
Well if you're outputting it to 12 output pins it looks like you're
using GRAY code or something like it. i.e.
1 => 000000000001
2 => 000000000010
2 => 000000000100
---or---
1 => 000000000001
2 => 000000000011
2 => 000000000111

If this is the case, just use a lookup table
ie case intIn is
when 0=> vecOut <= "000000000000";
when 1=> vecOut <= "000000000001";
etc...

This is a bit of a waste of resources though when 4 pins would do just
as well using the simpler conv_std_integer function and the
std_logic_unsigned library
 
I am unable to understand that why u are defing the counter value as
integer . U can define as std_logic_vector .
or
U can use the conversion function as--
CONV_STD_LOGIC_VECTOR conversion function:

ENTITY adder IS
PORT (op1, op2 : IN UNSIGNED(7 DOWNTO 0);
result : OUT STD_LOGIC_VECTOR(7 DOWNTO 0)
);
END adder;

ARCHITECTURE maxpld OF adder IS
BEGIN
result <= CONV_STD_LOGIC_VECTOR(op1 + op2, 8);
END maxpld;

I have updated your code pl check -
LIBRARY IEEE ;
USE IEEE.STD_LOGIC_1164.ALL ;
USE IEEE.STD_LOGIC_ARITH.ALL ;
USE IEEE.STD_LOGIC_UNSIGNED.ALL ;
entity count12 is
port (
clk : in std_logic;
bus_0_11: out std_logic_vector(11 downto 0)

);
end count12;
architecture beh of count12 is
signal flag : std_logic;
begin
Process(clk,flag)

-- my counter variable declaration
subtype counter_ty is integer range 0 to 4095; -- 12 bit counter,

variable my_counter : counter_ty := 0;

begin



if (flag = '1') then -- flag hi, output count to bus
bus_0_11 <= conv_std_logic_vector(my_counter, 12);
flag <= '0';
elsif (clk'event and clk = '1') then
my_counter := my_counter + 1;
end if;

end process;

end beh;
 
Many thanks to you and everyone for advice.

I defined counter as an integer because I wanted only 12 bits (count is
never bigger than 4095) and I saw that a subtype
would allow me to restrict the size to just what I needed.

Also, I was not sure about using
std_logic_vector as a counter because I wasn't sure if vector = vector + 1
would result in an addition or a bit AND operation. (Easy enough for
me to find out with a simple experiment).

The VHDL language is so strongly typed that everything I tried with subtypes
resulted
in an error in the MODELSIM compiler with no real clue as to the right way.

I will check out your suggestions, which seem to be excellent, on compiler.

Again, thanks
Tak


"aaaaaa" <anup@ct.com> wrote in message
news:c9b4f329a687e317a3197e4d104280ef@localhost.talkaboutprogramming.com...
I am unable to understand that why u are defing the counter value as
integer . U can define as std_logic_vector .
or
U can use the conversion function as--
CONV_STD_LOGIC_VECTOR conversion function:

ENTITY adder IS
PORT (op1, op2 : IN UNSIGNED(7 DOWNTO 0);
result : OUT STD_LOGIC_VECTOR(7 DOWNTO 0)
);
END adder;

ARCHITECTURE maxpld OF adder IS
BEGIN
result <= CONV_STD_LOGIC_VECTOR(op1 + op2, 8);
END maxpld;

I have updated your code pl check -
LIBRARY IEEE ;
USE IEEE.STD_LOGIC_1164.ALL ;
USE IEEE.STD_LOGIC_ARITH.ALL ;
USE IEEE.STD_LOGIC_UNSIGNED.ALL ;
entity count12 is
port (
clk : in std_logic;
bus_0_11: out std_logic_vector(11 downto 0)

);
end count12;
architecture beh of count12 is
signal flag : std_logic;
begin
Process(clk,flag)

-- my counter variable declaration
subtype counter_ty is integer range 0 to 4095; -- 12 bit counter,

variable my_counter : counter_ty := 0;

begin



if (flag = '1') then -- flag hi, output count to bus
bus_0_11 <= conv_std_logic_vector(my_counter, 12);
flag <= '0';
elsif (clk'event and clk = '1') then
my_counter := my_counter + 1;
end if;

end process;

end beh;
Click to expand...
 
Takuon,
For more more tips see the paper,
"VHDL Math Tricks of the Trade"

which is available at:
http://www.synthworks.com/papers/

Cheers,
Jim
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jim Lewis
Director of Training mailto:Jim@SynthWorks.com
SynthWorks Design Inc. http://www.SynthWorks.com
1-503-590-4787

Expert VHDL Training for Hardware Design and Verification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Many thanks to you and everyone for advice.

I defined counter as an integer because I wanted only 12 bits (count is
never bigger than 4095) and I saw that a subtype
would allow me to restrict the size to just what I needed.

Also, I was not sure about using
std_logic_vector as a counter because I wasn't sure if vector = vector + 1
would result in an addition or a bit AND operation. (Easy enough for
me to find out with a simple experiment).

The VHDL language is so strongly typed that everything I tried with subtypes
resulted
in an error in the MODELSIM compiler with no real clue as to the right way.

I will check out your suggestions, which seem to be excellent, on compiler.

Again, thanks
Tak


"aaaaaa" <anup@ct.com> wrote in message
news:c9b4f329a687e317a3197e4d104280ef@localhost.talkaboutprogramming.com...

I am unable to understand that why u are defing the counter value as
integer . U can define as std_logic_vector .
or
U can use the conversion function as--
CONV_STD_LOGIC_VECTOR conversion function:

ENTITY adder IS
PORT (op1, op2 : IN UNSIGNED(7 DOWNTO 0);
result : OUT STD_LOGIC_VECTOR(7 DOWNTO 0)
);
END adder;

ARCHITECTURE maxpld OF adder IS
BEGIN
result <= CONV_STD_LOGIC_VECTOR(op1 + op2, 8);
END maxpld;

I have updated your code pl check -
LIBRARY IEEE ;
USE IEEE.STD_LOGIC_1164.ALL ;
USE IEEE.STD_LOGIC_ARITH.ALL ;
USE IEEE.STD_LOGIC_UNSIGNED.ALL ;
entity count12 is
port (
clk : in std_logic;
bus_0_11: out std_logic_vector(11 downto 0)

);
end count12;
architecture beh of count12 is
signal flag : std_logic;
begin
Process(clk,flag)

-- my counter variable declaration
subtype counter_ty is integer range 0 to 4095; -- 12 bit counter,

variable my_counter : counter_ty := 0;

begin



if (flag = '1') then -- flag hi, output count to bus
bus_0_11 <= conv_std_logic_vector(my_counter, 12);
flag <= '0';
elsif (clk'event and clk = '1') then
my_counter := my_counter + 1;
end if;

end process;

end beh;
Click to expand...
 
Many interesting papers there.

Am reading.

Thanks
Tak

"Jim Lewis" <Jim@SynthWorks.com> wrote in message
news:1129khvhi53u457@corp.supernews.com...
Takuon,
For more more tips see the paper,
"VHDL Math Tricks of the Trade"

which is available at:
http://www.synthworks.com/papers/

Cheers,
Jim
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jim Lewis
Director of Training mailto:Jim@SynthWorks.com
SynthWorks Design Inc. http://www.SynthWorks.com
1-503-590-4787

Expert VHDL Training for Hardware Design and Verification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Many thanks to you and everyone for advice.

I defined counter as an integer because I wanted only 12 bits (count is
never bigger than 4095) and I saw that a subtype
would allow me to restrict the size to just what I needed.

Also, I was not sure about using
std_logic_vector as a counter because I wasn't sure if vector = vector +
1
would result in an addition or a bit AND operation. (Easy enough for
me to find out with a simple experiment).

The VHDL language is so strongly typed that everything I tried with
subtypes resulted
in an error in the MODELSIM compiler with no real clue as to the right
way.

I will check out your suggestions, which seem to be excellent, on
compiler.

Again, thanks
Tak


"aaaaaa" <anup@ct.com> wrote in message
news:c9b4f329a687e317a3197e4d104280ef@localhost.talkaboutprogramming.com...

I am unable to understand that why u are defing the counter value as
integer . U can define as std_logic_vector .
or
U can use the conversion function as--
CONV_STD_LOGIC_VECTOR conversion function:

ENTITY adder IS
PORT (op1, op2 : IN UNSIGNED(7 DOWNTO 0);
result : OUT STD_LOGIC_VECTOR(7 DOWNTO 0)
);
END adder;

ARCHITECTURE maxpld OF adder IS
BEGIN
result <= CONV_STD_LOGIC_VECTOR(op1 + op2, 8);
END maxpld;

I have updated your code pl check -
LIBRARY IEEE ;
USE IEEE.STD_LOGIC_1164.ALL ;
USE IEEE.STD_LOGIC_ARITH.ALL ;
USE IEEE.STD_LOGIC_UNSIGNED.ALL ;
entity count12 is
port (
clk : in std_logic;
bus_0_11: out std_logic_vector(11 downto 0)

);
end count12;
architecture beh of count12 is
signal flag : std_logic;
begin
Process(clk,flag)

-- my counter variable declaration
subtype counter_ty is integer range 0 to 4095; -- 12 bit counter,

variable my_counter : counter_ty := 0;

begin



if (flag = '1') then -- flag hi, output count to bus
bus_0_11 <= conv_std_logic_vector(my_counter, 12);
flag <= '0';
elsif (clk'event and clk = '1') then
my_counter := my_counter + 1;
end if;

end process;

end beh;
Click to expand...
 
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