Conditional expressions are supported in the following contexts:
- General Expression
- Initializers for constants, signals, and variables
- Attribute specifications
- Generic map, port map (interface association list)
- In Function return statements
- Conditional or Unaffected expression
Examples:
General
Expression:
out1 <= (in1 xor C when C1 = '0' else in1 and C) when in1 > C else
(in1 or C when C1 = '0' else in1 or C);Initializers for constants, signals, and
variables:
constant C: std_logic_vector(3 downto 0) := "1101" when C1 = '0' else"1000";
out1 <= (in1 xor C when C1 = '0' else in1 and C) when in1 > C else
(in1 or C when C1 = '0' else in1 or C);Attribute
specifications:
attribute USE_DSP48 of p1 : signal is "yes" when dsp = 1 else "no";Interface association
list:
entity bot is
generic (C1: std_logic := '0');
port(in1: in std_logic_vector(3 downto 0);
out1: out std_logic_vector(3 downto 0));
end entity bot;
u0: bot generic map(C1 => C1) port map (in1 => in1 when C1 = '1' else in2,out1 => out1);In Function return
statements:
function Mux4_3 (
Sel : std_logic_vector(1 downto 0);
A, B, C, D : std_logic_vector
) return std_logic_vector is
begin
return Mux4(Sel, A, B, C, D) when C1 = 1 else Mux4_2(Sel, A, B, C, D) ;
end function Mux4_3 ;Unaffected
expression:
package body MuxPkg is
function Mux4 (
Sel : std_logic_vector(1 downto 0);
A, B, C, D : std_logic_vector
) return std_logic_vector is
begin
return A when Sel = "00" else unaffected ;
return B when Sel = "01" else unaffected ;
return C when Sel = "10" else unaffected ;
return D when Sel = "11" else unaffected ;
return (A'range => 'X') ;
end function Mux4 ;
end package body MuxPkg ;