Re: [myhdl-list] List Of Constants

[Christopher F. <chr...@gm...>]

]
>
> thanks for the attention,
> I created a gist: https://gist.github.com/josyb/af6b7809d976b2559ae4
>
> The _example_ is distilled from a RGB to YCrCb converter, but the method
> will also be useful in convolution filters (edge detectors etc.) and
> other matrix-like operations.
>

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)
         @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.

Hope that helps,
Chris