Wednesday, April 9, 2008

VHDL Notes

1) .acf: pin assignment and configuration file
2) .mif: memory initialization file

3) LPM Components

Altera MAX+PlusII contains a Library of Parameterized Modules(LPM) that allows implementation of devices such as RAM, ROM, arithmetic devices, etc. The size of the devices are parameterized. That is, the number of bits in the operands are specified at the time an instance of the component is made. In order to use these components, you must declare the LPM library(LIBRARY lpm;) and specify which package to use in this library(USE lpm.lpm_components.all;). The following example shows how to use a LPM add/subtract device to create a 32-bit add/subtract unit.

LPM Example

USE ieee.std_logic_1164.all;
USE lpm.lpm_components.all;

ENTITY add_subt IS
PORT(a, b: IN std_logic_vector(31 downto 0);
a_s: IN std_logic;
answer: OUT std_logic_vector(31 downto 0));
END add_subt;
ARCHITECTURE struct OF add_subt IS
-- u1 is an arbitrary name of the instance
u1: lpm_add_sub -- This is the name of the component
GENERIC MAP(lpm_width => 32)
-- data, datab, add_sub, result are the formal parameter names
PORT MAP( dataa => a, datab => b, add_sub => a_s,
result => answer);
END struct;

A list of LPM components is available using HELP-> megafunctions/LPM in Altera MAX+PlusII.