Inferring a ROM

Hello,

here's an example for ROM inferred from HDL, just a few snippets

--- Quote Start ---

GENERIC

(

NNCO : INTEGER := 10; -- output amplitude resolution

NAKKUI : INTEGER := 10; -- akku integer bits = phase resolution

);

--

--

ARCHITECTURE rtl OF nco IS

CONSTANT ROMSIZE : INTEGER := 2**(NAKKUI-1);

CONSTANT ROMMAX : INTEGER := 2**(NNCO-1)-1;

TYPE SINTAB IS ARRAY(0 TO ROMSIZE-1) OF STD_LOGIC_VECTOR (NNCO-2 DOWNTO 0);

SIGNAL SINROM: SINTAB;

BEGIN

-- For FPGA devices, this construct infers ROM sine table,

-- for RAMless devices (MAX II) an LE based table instead

-- only the 0..pi positive half is represented

GENROM:

FOR idx in 0 TO ROMSIZE-1 GENERATE

CONSTANT x: REAL := SIN(real(idx)*MATH_PI/real(ROMSIZE));

CONSTANT xn: UNSIGNED (NNCO-2 DOWNTO 0) := CONV_UNSIGNED(INTEGER(x*real(ROMMAX)),NNCO-1);

BEGIN

SINROM(idx) <= STD_LOGIC_VECTOR(xn);

END GENERATE;

--- Quote End ---

I hope the method can be seen from the snippets.

Regards,

Frank