Re: [myhdl-list] Constant ints in interfaces

[SHEN C. <she...@co...>]

Hi all,

I encountered similar problem recently. This is a generic problem in 
the current implementation of interface.

In your code, the following line is critical:
         tiWIDTH_FPN = self.WIDTH_FPN

With this line, Python creates a local variable named "tiWIDTH_FPN".

In the previous versions of MyHDL, during conversion/elaboration, we 
put all local variables to "symdict".
I found two places where symdict is constructed, in _extractHier and in 
_analyzeGens:
   - 
https://github.com/jandecaluwe/myhdl/blob/master/myhdl/_extractHierarchy.py#L317
   - 
https://github.com/jandecaluwe/myhdl/blob/master/myhdl/conversion/_analyze.py#L149

Unfortunately, in the current implementation of interface, I couldn't 
find a place where self.WIDTH_FPN being added to symdict.

I recently found that, if a signal isn't included in symdict, it will 
appear as constant in converted code.
This is the origin of the remaining caveat I mentioned in pull request 
21 (https://github.com/jandecaluwe/myhdl/pull/21).

One workaround is simply to create a local copy of all signals in the 
interface.
In my project, I even created an Interface base class, and defined an 
signals() member method, so in the logic generators I can write:
    tiWIDTH_FPN, tiWIDTH_PRNU = self.signals()

Unfortunately, Python does not allow the following:
    createLocalVars( self.signals() )
so you will have to hand-write the left-hand-side of the assignment, in 
order to create local variables.



regards,
shenchne




On 2015-03-16 18:03, Josy Boelen wrote:

>> class Interface(object): def __init__(self): self.a = 
>> Signal(intbv(0,
>> min=-1000, max=1000)) self.c = 10 where c gets converted as
>> interface_name.c. My understanding from the docs is that this should 
>> be
>> supported, but I might be missing something. I noticed this 
>> previously
>> with IntEnum,
>
> but
>
> Henry,
>
> I noticed similar behaviour when using a class (as I also have local
> functions in the class), here is my code:
> class CorrectionCoefficients(object):
> ''' a VHDL-record like object '''
> def __init__(self, WIDTH_PRNU, WIDTH_FPN, p = 0, f = 0):
> self.WIDTH_FPN = WIDTH_FPN
> self.WIDTH_PRNU = WIDTH_PRNU
> self.fpn = Signal(intbv(f)[WIDTH_FPN:])
> self.prnu = Signal(intbv(p)[WIDTH_PRNU:])
>
> def toCorrectionCoefficients(self, v):
> # need an unique name as 'alias' otherwise the 'self.WIDTH_FPN'
> shows up as a constant in the VHDL
> tccWIDTH_FPN = self.WIDTH_FPN
> @always_comb
> def tcc():
> lv = v
> self.fpn.next = lv[tccWIDTH_FPN:]
> self.prnu.next = lv[:tccWIDTH_FPN]
>
> return tcc
>
> def tointbv(self, y):
> ''' build a flattened vector from the record's elements in
> ascending order'''
> # need an unique name as 'alias' otherwise the 'self.WIDTH_FPN'
> shows up as a constant in the VHDL :)
> tiWIDTH_FPN = self.WIDTH_FPN
>
> @always_comb
> def ti():
> y.next[tiWIDTH_FPN:] = self.fpn
> y.next[:tiWIDTH_FPN] = self.prnu
>
> return ti
>
> Regards,
>
> Josy
>
>
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