signal update problem

[sohannin]

I have a small part in my code like this (this is completely bogus but the
idea is the same):

process (ck)
....
internal_sum_2(0) <= internal_sum(0) XOR my_signal(0);
internal_sum_2(7 downto 1) <= internal_sum(7 downto 1) XOR "0000001";

sum <= internal_sum_2;
end process;
....

So this process is synchronous and signals update the sum which is
out-port. But why do they update the sum at both instances, i.e. the first
clause updating only the lowest bit of internal_sum_2 causes a change in
the output port "sum" immediately even though statements inside the
process should be sequential? My intention is to first construct the whole
8-bit vector and update the output port's all bits at the same time. What
am I doing wrong?

 

[amitesh]

you should put sum in a separate process with internal_sum_2(7) in the
sensitivity list.
sohannin wrote:

I have a small part in my code like this (this is completely bogus but the
idea is the same):

process (ck)
...
internal_sum_2(0) <= internal_sum(0) XOR my_signal(0);
internal_sum_2(7 downto 1) <= internal_sum(7 downto 1) XOR "0000001";

sum <= internal_sum_2;
end process;
...

So this process is synchronous and signals update the sum which is
out-port. But why do they update the sum at both instances, i.e. the first
clause updating only the lowest bit of internal_sum_2 causes a change in
the output port "sum" immediately even though statements inside the
process should be sequential? My intention is to first construct the whole
8-bit vector and update the output port's all bits at the same time. What
am I doing wrong?

 

[anupam]

Are you sure about the code written here is the same as code you are
running?
Because this happens when the internal_sum or the sum is a variable
.......
Shouldn't happen in this case ....
The signals are updated sequentially after a delta delay in a
process....

regards,
Anupam Jain

 

[sohannin]

On Tue, 31 Jan 2006 05:57:17 +0200, anupam <meanupam@gmail.com> wrote:

Yes, quite sure.

Internal sum wasn't a variable, but now it is. And now it works, for some
reason. I had to change all the internal signals to variables to cause the
sum to update only when the result is ready.

Are you sure about the code written here is the same as code you are
running?
Because this happens when the internal_sum or the sum is a variable
......
Shouldn't happen in this case ....
The signals are updated sequentially after a delta delay in a
process....

 

[sohannin]

On Mon, 30 Jan 2006 11:29:46 +0200, amitesh <fd97103@gmail.com> wrote:

you should put sum in a separate process with internal_sum_2(7) in the
sensitivity list.

Hmm, that's a good idea, thanks! Although it now works with variables.