Re: [myhdl-list] MEP 107 assessment

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

On 06/07/2012 09:11 PM, Christopher Felton wrote:
> On 6/5/2012 3:52 PM, Jan Decaluwe wrote:
>> I have read and thought about MEP 107. Here is my initial
>> assessment.
>>
>> This MEP is strictly about conversion. This is explained in
>> the first paragraph, but I think it should be mentioned in
>> the title also, because this has proven to be an eternal source
>> of confusion. It should be made clear that all modeling
>> aspects being discussed are supported by MyHDL as it is today.
>
> All aspects being discussed are almost supported for modeling today.  It
> has been reported that the @always_comb decorator fails to extract the
> sensitivity list if a signal is buried in a structure.  I have 4
> examples below that demonstrate the issue (a control and 3 fails).
> There is the limitation that the structures cannot be used on the right
> hand side currently (at lest for the version of 0.8dev I tested this with).

always_comb is a rather "low-level" decorator, very close to
implementation and synthesizable code. I don't think it has
many uses in high-level modeling. Therefore, I don't think it
should try to support all kinds of high-level data structures.

I think things should currently work for lists of Signals, even
"hetero_list" unless not all items are Signals. In that case,
I think you get what you deserve :-) (even in Python,
I think lists are intended to consist of similar objects.)

But for dicts, I don't see the case. Again here, in
general, all members should become part of the sensitivity
list. We do that for lists, but I don't really see the
use case for dynamically indexed dicts. And if it's only
static indexing - again, attributes are the right tool.

I take the point for attribute lookup though - patches
welcome.

> In [76]: x = Signal(False)
>       ...: y = Signal(False)
>       ...: con1 = {'x':Signal(False)}
>       ...: con2 = [Signal(False),
>                    'gibberish',
>                    Signal(intbv(0, min=-234, max=19987))]
>       ...: class Container(object): x = Signal(False)
>       ...: con3 = Container()
>       ...:
>
> In [77]: @always_comb
>       ...: def sim_sig():
>       ...:     x.next = y
>       ...:
>
> In [78]: @always_comb
>       ...: def sim_con1():
>       ...:     x.next = con1['x']
>       ...:
> ---------------------------------------------------------------------------
> AlwaysCombError                           Traceback (most recent call last)
> ...
> AlwaysCombError: sensitivity list is empty
>
> In [79]: @always_comb
>       ...: def con2():
>       ...:     x.next = con2[0]
>       ...:
> ---------------------------------------------------------------------------
> AlwaysCombError                           Traceback (most recent call last)
> ..
> AlwaysCombError: sensitivity list is empty
>
> In [80]: @always_comb
>       ...: def sim_con3():
>       ...:     x.next = con3.x
>       ...:
> ---------------------------------------------------------------------------
> AlwaysCombError                           Traceback (most recent call last)
> ...
> AlwaysCombError: sensitivity list is empty
>
>
> Regards,
> Chris F.
>
>
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-- 
Jan Decaluwe - Resources bvba - http://www.jandecaluwe.com
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