Generate statement

• A concurrent statement used to create regular structures or conditional structures during elaboration.

• Used to create multiple copies of components , processes or blocks.

• It provides a compact description of regular structures such as memories , registers and counters.

• Two flavors of generate statement are:

– for … generate
• Number of copies is determined by a discrete range.
– if … generate
• Zero or one copy is made conditionally.

• Range must be a computable integer in any of the following forms:
– integer_expression to integer_expression.
– integer_expression downto integer_expression.
– Each integer_expression evaluates to an integer.

Syntax :

Label: for ParameterName in Range generate
[Declarations...
begin]
ConcurrentStatements...
end generate [Label];
Label: if Condition generate
[Declarations...
begin]
ConcurrentStatements...
end generate [Label];

Where:

architecture – begin - - end
block – begin - - end
generate – begin - - end

Rules :
• The Range and Condition must both be static, i.e. they cannot include signals.
• The Label at the beginning of the generate statement cannot be omitted

Synthesis:
• Synthesis is straightforward, but not all synthesis tools support generate!

Example:

architecture ABC of full_add4 is
component full_add
port (PA , PB , PC : in std_logic ;
PCOUT , PSUM : out std_logic) ;
end component ;
signal c: std_logic_vector(4 downto 0);
begin
c(0) <= cin ;
-- cin is declared in entity
GK : for k in 3 downto 0 generate
FA :full_add port map(A(k),B(k),C(k),C(k+1),SUM(k);
end generate GK ;
cout <= c(4) ;
-- cout is declared in entity
end ABC ;

infers



Another example

architecture SHIFTER_ARCH of SHIFTER is
component DFF
port (D , CLK : in std_logic ;
Q : out std_logic) ;
end component ;
begin
GK : for k in 0 to 3 generate
GK0 : IF k=0 generate
DFILPFLOP : DFF port map (count , clock , Q(k));
end generate GK0 ;
GK1_3 : if k > 0 generate
DFILPFLOP : DFF port map (Q(k-1), clock , Q(k));
end generate GK1_3 ;
end generate GK ;
end SHIFTER_ARCH ;


infers



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