INFO:Xst:1304 -- precise definition anyone?

[Joseph]

Hello,

I am using VHDL and XST. I read some all the older threads that
mention the info/warning:

INFO:Xst:1304 - Contents of register <slv_ip2bus_data> in unit
<user_logic> never changes during circuit operation. The register is
replaced by logic.

And I still don't have a clear idea of why I am getting this problem in
my code. Rather than have you debug my code (though I can post if
helpful), can someone describe, in as much detail as you can stand,
what causes this message? I have no doubt it is my poor coding, but
hope a clear description can help me tidy things up. I think I am
using good FSM style (clk process to change state, comb process to get
next state, output process based on current state).

Any advice or pointers to documentation on this message appreciated...

Joey

 

[Joseph]

It seems that posting here (or the fpga group) clears my head (I think
I've answerd myself 3 times now within 24hrs of posting)... figured out
that my state machine setup was essentially correct, but I was not
clocking my registers, sort of assumed they would be updated (and
'saved') in the output process when I said stuff like:

my_ff <= my_ff and other_signal;

but since this process was combinational, my_ff wasn't ever going to
become a real FF. I guess these are the growing pains of transforming
from a programmer to a HW designer. Thanks to anyone who read this
thread and thought about it at all (sorry for my ramblings). If any of
my analysis is flawed, please set me straight.

Joey

 

[Ben Twijnstra]

Hi Joey,

It seems that posting here (or the fpga group) clears my head (I think
I've answerd myself 3 times now within 24hrs of posting)... figured out
that my state machine setup was essentially correct, but I was not
clocking my registers, sort of assumed they would be updated (and
'saved') in the output process when I said stuff like:

my_ff <= my_ff and other_signal;

but since this process was combinational, my_ff wasn't ever going to
become a real FF. I guess these are the growing pains of transforming
from a programmer to a HW designer.

Is it possible for you to send me a snippet of the failing and the working
code? I'm currently writing a one-day training called "VHDL design for
software engineers" and would like to see if this is a thinko I haven't
covered yet.

Don't send code to the address specified in the header. Send it to
[myfirstname].[mylastname] at gmail dot com. Oh, and don't try to pronounce
my last name. It may hurt your tongue.

Best regards,


Ben Twijnstra