Re: [myhdl-list] List Of Constants

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

> I looked at your code a little closer, first
> you want to create a `tuple` of ints or `tuple`
> of `intbv`.  Because we are using a ROM and you
> want to access multiple index at a time you need
> to access first:
> 
>      def simplefunc( Coeff, Clk, DA, DB, Q):
>          ''' a simple operation, just for the effect ... '''
> 
>          Coeff = tuple(Coeff)
>           <at> always_seq( Clk.posedge, reset = None)
>          def calc():
>              c0 = Coeff[0]
>              c1 = Coeff[1]
>              Q.next = c0 * DA + c1 * DB
> 
> The converter doesn't detect the constant/literal
> index value so it doesn't replace the const with
> the explicit value (this could possibly be a MEP).
> 
> To use the ROM structure you need to capture with
> a variable first, the generated code will be kinda
> odd (optimized away) because it is generate for a
> variable index instead of a const.
> 
> You could use a list-of-signals with initial values
> but initial values support has not been enabled because
> support was inconsistent between various synthesis tools:
> http://dev.myhdl.org/ideas/initial-values.html
> 
> At one point someone had a patch that enabled initial
> value support for list-of-signals (i.e. RAM) but we
> never finished verifying support across the major
> synthesis tools.
> 
<snip>

Chris,

I tried that code, and although it functions, the VHDL code doesn't get any 
prettier. Also the method stays cumbersome for large(r) coefficient arrays.
I can live with my workaround (spelling out every coefficient in the call) and 
put my hopes on future improvements on the conversion process. 

You indirectly answer my question: initial values are not supported - so my 
workaround of embedding the constant in a Signal can't work. Close but no cigar 
:)

Regards,

Josy