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

[Angel E. <ang...@gm...>]

On Thu, Oct 11, 2012 at 5:45 PM, Christopher Felton
<chr...@gm...> wrote:
> 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

Sorry Chris,

I made a typo on my example. s_input is 30 bits long, not 60, i.e.

s_input = Signal(intbv(0)[30:])

The problem is that var_test is 30 bits long rather than 15 as I expected.

Cheers,

Angel