myhdl-list

[myhdl-list] strange problem

[Neal B. <ndb...@gm...>]

I'm still trying to wrap my head around myhdl.  This one is weird.

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?

Re: [myhdl-list] strange problem

[Christopher F. <chr...@gm...>]

On Tue, Mar 17, 2009 at 9:59 AM, Neal Becker <ndb...@gm...> wrote:

> I'm still trying to wrap my head around myhdl.  This one is weird.
>
> 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?
>
>
I am not the most knowledgeable with this issue.  But I think it is an issue
of scope.  In your example the "input_sample_cnt" is part of the testbench
and not part of the stimulus generator.  I forgot the relationship that the
"Signal" introduces.  There should be a way to use simple variables as you
outline (need to check the cookbooks and examples to refresh my memory).
If you make your variable a "Signal+, and use input_sample_cnt.next = ... it
will work.  As mentioned above  I believe there is a method to use variable
but I don't know off the top of my head.

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

[myhdl-list] polytopes within MYHDL

[David B. <dav...@ya...>]

Has anyone ever developed a polytopes arithmetic operation in MYHDL, which was also successfully synthesize such a design to VHDL or Verilog?  Polytopes are a sort of enumerated integer type operation.   Thanks, David Blubaugh


      

Re: [myhdl-list] strange problem

[Neal B. <ndb...@gm...>]

Jan Decaluwe wrote:

> 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
That worked fine, until I needed to access (read) a variable also in another 
generator.

I find that:

x = Signal (0)

def gen1...
  x.next = x + 1

def gen2...
  print x

Works fine, but if x was just a simple variable, say int, we have the 
referenced before assignment (of course, using x = x+1 instead of x.next = 
x+1).

Other than using a Signal, any other solution?  It seems silly to use Signal 
for something that is just part of my test setup.

Re: [myhdl-list] strange problem

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

Neal Becker wrote:

> That worked fine, until I needed to access (read) a variable also in another 
> generator.
> 
> I find that:
> 
> x = Signal (0)
> 
> def gen1...
>   x.next = x + 1
> 
> def gen2...
>   print x
> 
> Works fine, but if x was just a simple variable, say int, we have the 
> referenced before assignment (of course, using x = x+1 instead of x.next = 
> x+1).
> 
> Other than using a Signal, any other solution?  It seems silly to use Signal 
> for something that is just part of my test setup.

You could declare the int x as global inside your generators.

Or you could declare a global intbv and use x[:] = x + 1.

In both cases though, you loose the determinism that signals give
you. In other words, the behavior will depend on the (unspecified)
order in which generators are run by the simulator.

Jan

-- 
Jan Decaluwe - Resources bvba - http://www.jandecaluwe.com
    Python as an HDL: http://www.myhdl.org
    VHDL development, the modern way: http://www.sigasi.com
    Analog design automation: http://www.mephisto-da.com
    World-class digital design: http://www.easics.com