Re: [myhdl-list] Conversion error: Type mismatch with earlier assignment

[Josy B. <jos...@gm...>]

Hi Guy,
 
> I actually run into this issue quite often, probably because of my 
liberal use of variables to store intermediate results. Here's a code 
snippet that triggers the conversion error:
> 
> ---
> 
> from myhdl import *
> 
> def mymodule(clk_i, reset_i, count_o):
> 
>     count_r_s = Signal(intbv(0)[32:])
>     
>      <at> always_seq(clk_i.posedge, reset=reset_i)
>     def logic():
>         count_v = count_r_s[:]
>         count_v = count_v + 1
>         count_r_s.next = count_v
> 
>      <at> always_comb
>     def outputs():
>         count_o.next = count_r_s
>     
>     return instances()
> 
> if __name__ == "__main__":
>     clk_i = Signal(bool(0))
>     reset_i = ResetSignal(0, active=1, async=False)
>     count_o = Signal(intbv(0)[32:])
>     toVHDL(mymodule, clk_i, reset_i, count_o)
> 
> ---
> 
> 
> Of course, the fix is to change the second variable assignment to:
> 
> count_v[:] = count_v + 1
> 
> but this is not necessarily obvious from the error message, especially 
if you're new to Python/MyHDL. Also, if the same variable gets assigned 
many times same function, it may not always be easy to find the 
assignment that overwrites the variable (instead of just its value).
> 
To my idea, you should have been able to write it as follows:
def mymodule(clk_i, reset_i, count_o):

    count_r_s = Signal(intbv(0)[32:])

    @always_seq(clk_i.posedge, reset=reset_i)
    def logic():
        count_v = count_r_s
        count_v = count_v + 1
        count_r_s.next = count_v

    @always_comb
    def outputs():
        count_o.next = count_r_s

    return instances()

so without the [:].
Anyway also when written like this we get the same error message for the 
same line. What happens, IMO, is that the converter thinks it sees a 
second, duplicate variable declaration and complains ... If you add the 
[:] the converter follows another path, as you are slicing, and doesn't 
do the 'check' and all ends well. I only use variables sparingly and the 
one example I could immediately find does a single assignment only:
    endval = int(startValue) + int(Length)
explaining my 'rare' remark.
I'm not sure yet but this may be a bug. Can you show me some code where 
you have a more elaborate use of a variable - saving me from writing one 
myself?

Best regards,

Josy