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.