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AR# 22495

8.2i XST - What does the following error mean: "ERROR:Xst:772 - "Attribute is not authorized : 'succ'."?

Description

What does the following error mean?

"ERROR:Xst:772 - "Attribute is not authorized : 'succ'."

The following is my example code:

============================

type state_type is (s0, s1);

signal state : state_type;

begin

process (clk, reset)

begin

if (reset = '1') then

outdata <= '0' ;

state <= s0;

elsif rising_edge(clk) then

if (flag = '1') then

state <= state_type'succ(state);

else

state <= s0 ;

end if;

end if ;

end process ;

=================================

Solution

The VHDL LRM does not allow you to access user-defined attributes in this manner; consequently, the error message is correct. The LRM allows only the ability to access predefined attributes.

To eliminate this error, you can write your code as follows:

=============================================================

type state_type is (s0, s1);

signal state : state_type;

begin

process (clk, reset)

begin

if (reset = '1') then

outdata <= '0' ;

state <= s0;

elsif rising_edge(clk) then

if (flag = '1') then

state <= s1;

else

state <= s0 ;

end if;

end if ;

end process ;

=========================================================================

AR# 22495
Date 12/15/2012
Status Active
Type General Article