Re: [myhdl-list] Problems using signal slices and variables

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

On 10/11/2012 6:10 AM, Angel Ezquerra wrote:
> Hi,
>
> I'm playing around with concatenating and slicing signals in MyHDL.
> I'm having some trouble with slicing in particular.
>
> I am having a hard time predicting what MyHDL will do when the code is
> converted to VHDL, and sometimes what I get seems wrong (or at least
> it is not what I expected).
>
> In particular, I've got the following code (note that the code has no
> purpose other than testing how MyHDL works):
>
>      s_input = Signal(intbv(0)[59:])
>      s_output = Signal(intbv(0)[59:])
>      s_slice = s_input(15, 0) # Use a shadow signal
>
>      @always(clk.posedge, rst.posedge)
>      def p_process():
>          if rst == 1:
>              max_value = s_input.max - 1
>              s_input.next = max_value
>              var_test = s_input[15:0] # I expect var_test to be a
> variable of range 14 downto 0, i.e. size 15
>              s_output.next = concat(s_input[15:0], s_input[30:15],
> s_input) # Total size: 15 + 15 + 30 = 60
>              s_output.next = concat(s_slice, s_input[30:15], s_input)
> # Total size: 15 + 15 + 30 = 60
>              s_output.next = concat(var_test, s_input[30:15], s_input)
> # Total size: 15 + 15 + 30 = 60
>          else:
>              pass
>

Not following your math for the last concat

 >  s_output.next = concat(var_test, s_input[30:15], s_input)

    var_test = 15 (14 downto 0)
    s_input[30:15] = 15 (29 downto 15 )
    s_input = 59 (58 downto 0)

trying to concat 89.

In [63]: s_input = Signal(intbv(0)[59:])
     ...: s_output = Signal(intbv(0)[59:])
     ...: var_test = s_input[15:0]
     ...: len(concat(var_test, s_input[30:15], s_input))
     ...:
Out[63]: 89

.chris