Subversion Repositories single_port

-- $Author: rpaley_yid $

-- $Date: 2003-01-14 21:48:10 $

-- $Header: /home/marcus/revision_ctrl_test/oc_cvs/cvs/single_port/VHDL/linked_list_mem_pkg.vhd,v 1.1.1.1 2003-01-14 21:48:10 rpaley_yid Exp $

-- $Locker

-- $Revision: 1.1.1.1 $

-- $State: Exp $

-- --------------------------------------------------------------------------

-- 

-- Purpose: This package implements functions to allocate, write, read, and

--          deallocate a linked list based memory.

--

-- 

-- References: 

--   1. The Designer's Guide to VHDL by Peter Ashenden

--      ISBN: 1-55860-270-4 (pbk.)

--   2. Writing Testbenches - Functional Verification of HDL models by 

--      Janick Bergeron | ISBN: 0-7923-7766-4

--

-- Notes: 

--

-- --------------------------------------------------------------------------

LIBRARY IEEE;

LIBRARY WORK;

USE IEEE.STD_LOGIC_1164.ALL;

USE WORK.single_port_pkg.all;

PACKAGE linked_list_mem_pkg IS

  -- data memory array type definition

  TYPE mem_array_typ IS ARRAY (0 TO PAGEDEPTH-1) OF data_typ;

  -- Define memory page linked list cell. This cell contains,

  -- the mem_array, starting page address, valid data array, and 

  -- the pointer to the next element in the linked list.

  TYPE mem_page_typ;

  -- pointer to next item in the linked list.

  TYPE mem_page_ptr IS ACCESS mem_page_typ;

  TYPE mem_page_typ IS RECORD

    mem_array : mem_array_typ; -- data memory

    -- This array is a flag which indicates if the corresponding

    -- address location inside mem_array contains valid data.

    data_valid_array : BIT_VECTOR( 0 TO PAGEDEPTH-1);

    page_address : addr_typ;

    next_cell : mem_page_ptr;

  END RECORD mem_page_typ;

  PROCEDURE rw_mem (

                   VARIABLE data : INOUT data_inter_typ;

                   VARIABLE addr : addr_typ;

                   VARIABLE write_flag : BOOLEAN;

                   VARIABLE next_cell : INOUT mem_page_ptr

                       );

  PROCEDURE deallocate_mem (

                            VARIABLE next_cell : INOUT mem_page_ptr

                           );

END PACKAGE linked_list_mem_pkg;

PACKAGE BODY LINKED_LIST_MEM_PKG IS

  -- --------------------------------------------------

  -- The purpose of this procedure is to write a memory location from 

  -- the linked list, if the particular page does not exist, create it.

  -- --------------------------------------------------  

  PROCEDURE rw_mem (

                      VARIABLE data : INOUT data_inter_typ;

                      VARIABLE addr : addr_typ;

                      VARIABLE write_flag : BOOLEAN;

                      VARIABLE next_cell : INOUT mem_page_ptr

  ) IS

   VARIABLE current_cell_v : mem_page_ptr; -- current page pointer

   VARIABLE page_address_v : addr_typ; -- calculated page address

   VARIABLE index_v        : INTEGER; -- address within the memory page

   VARIABLE mem_array_v : mem_array_typ;

   VARIABLE data_valid_array_v : BIT_VECTOR(0 TO PAGEDEPTH-1);

  BEGIN

    -- Copy the top of the linked list pointer to a working pointer

    current_cell_v := next_cell;

    -- Calculate the index within the page from the given address

    index_v := addr MOD PAGEDEPTH;

    -- Calculate the page address from the given address

    page_address_v := addr - index_v;

    -- Search through the memory to determine if the calculated

    -- memory page exists. Stop searching when reach the end of

    -- the linked list.

    WHILE ( current_cell_v /= NULL

            AND current_cell_v.page_address /= page_address_v) LOOP

      current_cell_v := current_cell_v.next_cell;

    END LOOP;

    IF write_flag THEN

      IF ( current_cell_v /= NULL AND -- Check if address exists in memory.

           current_cell_v.page_address = page_address_v

           ) THEN

        -- Found the memory page the particular address belongs to

        current_cell_v.mem_array(index_v) := TO_BITVECTOR(data);

        -- set memory location valid flag

        current_cell_v.data_valid_array(index_v) := '1';

      ELSE

        -- The memory page the address belongs to was not allocated in memory.

        -- Allocate page here and assign data.

      mem_array_v(index_v) := TO_BITVECTOR(data);

      data_valid_array_v(index_v) := '1';

      next_cell := NEW mem_page_typ'( mem_array => mem_array_v,

                                  data_valid_array => data_valid_array_v,

                                  page_address => page_address_v,

                                  next_cell => next_cell

                                );

      END IF;

    ELSE -- Read memory

      IF ( current_cell_v /= NULL AND -- Check if address exists in memory.

           current_cell_v.page_address = page_address_v AND

           current_cell_v.data_valid_array(index_v) = '1'

           ) THEN

        -- Found the memory page the particular address belongs to,

        -- and the memory location has valid data.

        data := TO_STDLOGICVECTOR(current_cell_v.mem_array(index_v));

      ELSE

        -- Trying to read from unwritten or unallocated 

        -- memory location, return 'U';

        data := (OTHERS => 'U');

      END IF;

    END IF;

  END PROCEDURE rw_mem;

  PROCEDURE deallocate_mem (

                            VARIABLE next_cell : INOUT mem_page_ptr

                           ) IS

    VARIABLE delete_cell_v : mem_page_ptr;

  BEGIN

    -- Deallocate the linked link memory from work station memory.

    WHILE next_cell /= NULL LOOP -- while not reached the end of the LL

      delete_cell_v := next_cell; -- Copy pointer to record for deleting

      next_cell := next_cell.next_cell; -- set pointer to next cell in LL

      deallocate(delete_cell_v); -- Deallocate current cell from memory.

    END LOOP;

  END PROCEDURE deallocate_mem;

END PACKAGE BODY LINKED_LIST_MEM_PKG;

-- $Log: not supported by cvs2svn $

-- Revision 1.1  2003/01/14 17:47:32  Default

-- Initial revision

--

-- Revision 1.1  2002/12/24 18:03:50  Default

-- Initial revision

--