variable step for loop

[cltsaig]

Hi all,
Can anyone check whether my VHDL code for variable step for-loop is
correct or not??? Many thanks!!!

------- C code example --------
int ip1;
for (ip1=1; ip1<=10; ip1+=2) {
....
}

------- VHDL code example -------
varible ip1 : integer;
for ip1 in 1 to 10 loop
ip1:=ip1+2;
....
end loop;

Stanley

 

[Alan Fitch]

Hi all,
Can anyone check whether my VHDL code for variable step for-loop is
correct or not??? Many thanks!!!

------- C code example --------
int ip1;
for (ip1=1; ip1<=10; ip1+=2) {
...
}

------- VHDL code example -------
varible ip1 : integer;
for ip1 in 1 to 10 loop
ip1:=ip1+2;
...
end loop;

Stanley

No it won't work. You can't assign to the loop parameter
in VHDL as it is a constant - VHDL effectively unrolls the loop
creating copies, and for each copy ip1 is a constant.

Also you don't have to declare the loop parameter ip1 - in
fact if you do, the loop parameter ip1 hides (makes invisible)
the variable ip1 - they are two different objects in VHDL!

Hence you need a separate variable to hold the doubled
index, e.g.

variable ip2 : natural range 0 to 10;

ip2 := 0;
for ip1 in 1 to 5 loop -- ip1 is implicitly declared
ip2 := ip2 + 2;
.... -- use ip2 in the indexing of course!
end loop;

regards

Alan

--
Alan Fitch
Consultant

DOULOS - Developing Design Know-how
VHDL * Verilog * SystemC * Perl * Tcl/Tk * Verification * Project
Services

Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, Hampshire, BH24
1AW, UK
Tel: +44 (0)1425 471223 mail:
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Fax: +44 (0)1425 471573 Web:
http://www.doulos.com

The contents of this message may contain personal views which are not
the
views of Doulos Ltd., unless specifically stated.

 

[Jim Lewis]

Stanley,

Hi all,
Can anyone check whether my VHDL code for variable step for-loop is
correct or not??? Many thanks!!!

------- C code example --------
int ip1;
for (ip1=1; ip1<=10; ip1+=2) {
...
}

------- VHDL code example -------
varible ip1 : integer;
for ip1 in 1 to 10 loop
ip1:=ip1+2;
...
end loop;

You can use a for loop to control the number of
iternations only. Hence one way to translate your
"C" code is:

variable ip1 : integer ;

for loop_var in 0 to 4 loop -- don't declare loop_var
ip1 := (loop_var * 2) + 1 ;
. . .

end loop;


Another way is to unroll the C code into its
equivalent while loop:

variable ip1 : integer ;

ip1 := 1 ;
while ip1 <= 10 loop
. . .

ip1 := ip1+2 ;
end loop ;


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

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

 

[cltsaig]

Hi Alan and Jim,
Greatly thanks from your feedback...I kinda perceived the error that I
made on my previous post.

Although, I had an another enigma need you expert/guru's feedback? The
concern is how to reproduce this C function into VHDL?? Is it feasible??
I'd declared a package that defines an floating point array.

void fun(float data[], int nn[], int ndim, int sign)
{
.....
}

------- VHDL code --------------------------------
package pack1 is
type array_fp32 is array (positive range <>) of fp32;
end pack1;

use work.pack1.all;
entity fun is
port(
data: in array_fp32 ;
nn: in array_integer;
ndim: in integer;
sign: in integer;
clk:in std_logic;
rst:in std_logic;
resultut array_fp32
);
end fun;


Kindest regards,
Stanley

 

[Alan Fitch]

Hi Alan and Jim,
Greatly thanks from your feedback...I kinda perceived the error that I
made on my previous post.

Although, I had an another enigma need you expert/guru's feedback? The
concern is how to reproduce this C function into VHDL?? Is it feasible??
I'd declared a package that defines an floating point array.

void fun(float data[], int nn[], int ndim, int sign)
{
....
}

------- VHDL code --------------------------------
package pack1 is
type array_fp32 is array (positive range <>) of fp32;
end pack1;

use work.pack1.all;
entity fun is
port(
data: in array_fp32 ;
nn: in array_integer;
ndim: in integer;
sign: in integer;
clk:in std_logic;
rst:in std_logic;
resultut array_fp32
);
end fun;

This should work fine, as long as you have also defined
the array_integer type somwehere.

You can have entities with unconstrained ports, though
not all synthesis tools are happy with them (assuming
of course that you instantatiate a componenent and
bind the ports so that the actual widths are known).

Alternatively you can write a procedure corresponding
to your function. Procedures with unconstrained ports
normally are fine with synthesis tools, if they result
in combinational logic. If they have a clock (as yours
seems to) then some synthesis tools don't like them.

Of course if you're not going to synthesise the code,
don't worry if it's synthesisable or not

regards

Alan

--
Alan Fitch
Consultant

DOULOS - Developing Design Know-how
VHDL * Verilog * SystemC * Perl * Tcl/Tk * Verification * Project
Services

Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, Hampshire, BH24
1AW, UK
Tel: +44 (0)1425 471223 mail:
(e-mail address removed)
Fax: +44 (0)1425 471573 Web:
http://www.doulos.com

The contents of this message may contain personal views which are not
the
views of Doulos Ltd., unless specifically stated.