Re: [myhdl-list] Re: range object

[Haitao Z. <ha...@gm...>]

On Thu, 03 Mar 2005 11:49:08 +0100, Jan Decaluwe <ja...@ja...> wrote:
> Haitao Zhang wrote:
> > Another nice to have :)
> >
> > In VHDL one could define a range type and define a constant with it,
> > so that one can associate a symbolic name say CTRL_FIELD with  7
> > DOWNTO 3, and then one can refer to register(CTRL_FIELD). In Verilog
> > one can probably get by with macro defines. However in Python the
> > native slicing is limited to integer arguments (?), so one has to
> > define two named constants instead of passing an indexing object.
> 
> This is not correct. Consider:
> 
> >>> from myhdl import intbv
> >>> a = intbv(0xffff)
> >>> CTRL_FIELD = slice(4, 2)
> >>> type(CTRL_FIELD)
> <type 'slice'>
> >>> a[CTRL_FIELD]
> intbv(3L)
> >>> a[CTRL_FIELD] = 0
> >>> hex(a)
> '0xFFF3L'
> 
> The slice object is not often used explicitly in Python code but
> probably deserves more attention. (Warning: toVerilog doesn't
> support his - as always, patches are welcome!).
> 

Thanks for the tip! This is exactly what I want for now. (Matlab
behaviour is probably an over kill unless one has no-contigous field,
which for hardware designer only happens under special circumstances).
I will see what I can do about toVerilog when I get that far.

Haitao

> > This feature is handy when one needs to define control register
> > fields. It allows one to define the named constants in one place.
> >
> > In Matlab one can index any vector with another vector. I don't see
> > why this shouldn't be doable in Python as well. Maybe just no need for
> > it, until the hardware designers come along? Is the simplest way to
> > overload __getslice__ to accept a tuple (defining range)?
> 
> (__getslice__ is deprecated, use __getitem__ instead. Look in
> the 0.4.1 code for intbv to see how slicing is implemented.)
> More than you probably need has been done by lots of people doing
> lots of work. Check out the Numeric Python extension for a Python
> with MatLab-like functionality. Also check SciPy. (Warning:
> there is a LOT of material to study.)
> 
> Regards, Jan
> 
> --
> Jan Decaluwe - Resources bvba - http://jandecaluwe.com
> Losbergenlaan 16, B-3010 Leuven, Belgium
>     Using Python as a hardware description language:
>     http://jandecaluwe.com/Tools/MyHDL/Overview.html
> 
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