[myhdl-list] always_comb from a change in Signal list does not get triggered

[Günter D. <dan...@we...>]

Hi,

I am trying to create a word wide shift register and the output register 
is connected with an always_comb to the output signal of the function. 
Now this always_comb gets only triggered one time, even so I see the 
output register signal change during the shift operation.

This is my code:

def pipe(clk,en,din, dout, N,width):

   pipe = [Signal(intbvSigned(width)) for i in range(N)]

   print "N: ", N

   @always(clk.posedge)
   def rtl1():
     if en:
       for i in downrange(N,1):
         print "i: %d"% i
         pipe[i].next = pipe[i-1]
       pipe[0].next = din
     print "pipe: %s"% pipe


   @always_comb
   def rtl2():
     print "pipe[N-1]: %d"% pipe[N-1]
     dout.next = pipe[N-1]


   return instances()



I attached the test bench for it. Running the test bench will fill the 
pipe with values and print the output dout.

I changed the code so that the pipe memory has only N-1 entries and dout 
being the Nth register, which worked fine. I just would like to know 
what I am doing wrong so that the always_comb gets not triggered anymore?


BTW, in the above example I am using a convenience function to create a 
signed intbv instance:

------------------------------------------------------

def intbvSigned(width, value=0):

   max = 2**(width-1)
   min = -max
   r = intbv(value, min, max)

   return r



Thanks for any help.

Guenter