Re: [myhdl-list] strange problem

[Jan D. <ja...@ja...>]

Neal Becker wrote:
> I'm still trying to wrap my head around myhdl.  This one is weird.

It is purely a Python scope issue. Consider:

def f():
    n = 0
    def g():
            n += 1
            print n
    g()

f()

Running this gives:

> python tmp.py
Traceback (most recent call last):
  File "tmp.py", line 8, in <module>
    f()
  File "tmp.py", line 6, in f
    g()
  File "tmp.py", line 4, in g
    n += 1
UnboundLocalError: local variable 'n' referenced before assignment


To understand what happens, consider that 'n += 1' is equivalent to:
  n = n + 1

When you *assign* to n somewhere locally, Python considers it a
local variable. As the n in the rhs as not been locally assigned yet,
you get the error.
Note that as long you don't assign to n, you would have read
access to the n in the enclosing scope.

For your case, put the initialization in the generator before
the while loop.

Jan

> 
> In my testbench/monitor, which was working, I just added a variable 
> 'input_sample_cnt':
> 
>     input_sample_cnt = 0
>     
>     @instance
>     def stimulus():
>         while (1):
>             yield clock.negedge
>             if (en):
>                 in_i.next = in_i_iter.next()
>                 in_q.next = in_q_iter.next()
>                 input_sample_cnt += 1
>                 
>             reset.next = 0
> 
> I get:
>     input_sample_cnt += 1
> UnboundLocalError: local variable 'input_sample_cnt' referenced before 
> assignment
> 
> But I've had this all along:
>     result_fd = file ('result', 'w')
>     count_fd = file ('count', 'w')
>     reset_fd = file ('reset', 'w')
>     x_fd = file ('x', 'w')
>     en_fd = file ('en', 'w')
>     oe_fd = file ('oe', 'w')
>     
>     @instance
>     def monitor():
>         while 1:
>             yield clock.posedge
>             ##print 'reset:', reset, 'en:', en, 'x:', x, 'count:', 
> to_hex(count), 'result:', to_hex(result)
>             if (oe):
>                 print >> result_fd, to_hex (result_i), to_hex (result_q)
>             print >> count_fd, to_hex (count)
>             print >> x_fd, to_hex (in_i), to_hex (in_q)
>             print >> reset_fd, to_hex (reset)
>             print >> en_fd, to_hex (en)
>             print >> oe_fd, to_hex (oe)
> 
> This seems functionally the same thing (other than using +=).  Why does this 
> latter work, but the former not?  What should I be doing instead?
> 
> 
> 
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-- 
Jan Decaluwe - Resources bvba - http://www.jandecaluwe.com
    Python as a hardware description language:
    http://www.myhdl.org