neorv32/rtl/core/neorv32_fifo.vhd

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2024-02-24 08:25:27 +00:00
-- #################################################################################################
-- # << NEORV32 - Generic Single-Clock FIFO Component >> #
-- # ********************************************************************************************* #
-- # BSD 3-Clause License #
-- # #
-- # The NEORV32 RISC-V Processor, https://github.com/stnolting/neorv32 #
-- # Copyright (c) 2024, Stephan Nolting. All rights reserved. #
-- # #
-- # Redistribution and use in source and binary forms, with or without modification, are #
-- # permitted provided that the following conditions are met: #
-- # #
-- # 1. Redistributions of source code must retain the above copyright notice, this list of #
-- # conditions and the following disclaimer. #
-- # #
-- # 2. Redistributions in binary form must reproduce the above copyright notice, this list of #
-- # conditions and the following disclaimer in the documentation and/or other materials #
-- # provided with the distribution. #
-- # #
-- # 3. Neither the name of the copyright holder nor the names of its contributors may be used to #
-- # endorse or promote products derived from this software without specific prior written #
-- # permission. #
-- # #
-- # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS #
-- # OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF #
-- # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE #
-- # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, #
-- # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE #
-- # GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED #
-- # AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING #
-- # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED #
-- # OF THE POSSIBILITY OF SUCH DAMAGE. #
-- #################################################################################################
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
library neorv32;
use neorv32.neorv32_package.all;
entity neorv32_fifo is
generic (
FIFO_DEPTH : natural := 4; -- number of fifo entries; has to be a power of two; min 1
FIFO_WIDTH : natural := 32; -- size of data elements in fifo
FIFO_RSYNC : boolean := false; -- false = async read; true = sync read
FIFO_SAFE : boolean := false; -- true = allow read/write only if data available
FULL_RESET : boolean := false -- true = reset all memory cells (cannot be mapped to BRAM)
);
port (
-- control --
clk_i : in std_ulogic; -- clock, rising edge
rstn_i : in std_ulogic; -- async reset, low-active
clear_i : in std_ulogic; -- sync reset, high-active
half_o : out std_ulogic; -- FIFO is at least half full
-- write port --
wdata_i : in std_ulogic_vector(FIFO_WIDTH-1 downto 0); -- write data
we_i : in std_ulogic; -- write enable
free_o : out std_ulogic; -- at least one entry is free when set
-- read port --
re_i : in std_ulogic; -- read enable
rdata_o : out std_ulogic_vector(FIFO_WIDTH-1 downto 0); -- read data
avail_o : out std_ulogic -- data available when set
);
end neorv32_fifo;
architecture neorv32_fifo_rtl of neorv32_fifo is
-- make sure FIFO depth is a power of two --
constant fifo_depth_c : natural := cond_sel_natural_f(is_power_of_two_f(FIFO_DEPTH), FIFO_DEPTH, 2**index_size_f(FIFO_DEPTH));
-- FIFO storage --
type fifo_mem_t is array (0 to fifo_depth_c-1) of std_ulogic_vector(FIFO_WIDTH-1 downto 0);
signal fifo_mem : fifo_mem_t; -- for fifo_depth_c > 1
signal fifo_reg : std_ulogic_vector(FIFO_WIDTH-1 downto 0); -- for fifo_depth_c = 1
-- FIFO control --
signal we, re : std_ulogic; -- write-/read-enable
signal w_pnt, r_pnt : std_ulogic_vector(index_size_f(fifo_depth_c) downto 0); -- write/read pointer
signal w_nxt, r_nxt : std_ulogic_vector(index_size_f(fifo_depth_c) downto 0);
-- read access pointer register for async. read --
signal r_pnt_ff : std_ulogic_vector(index_size_f(fifo_depth_c) downto 0);
-- status --
signal match, empty, full, half, free, avail : std_ulogic;
-- fill level --
signal diff : std_ulogic_vector(index_size_f(fifo_depth_c) downto 0);
begin
-- Access Control -------------------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
re <= re_i when (FIFO_SAFE = false) else (re_i and avail); -- SAFE = read only if data available
we <= we_i when (FIFO_SAFE = false) else (we_i and free); -- SAFE = write only if free space left
-- Pointers -------------------------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
pointer_update: process(rstn_i, clk_i)
begin
if (rstn_i = '0') then
w_pnt <= (others => '0');
r_pnt <= (others => '0');
elsif rising_edge(clk_i) then
w_pnt <= w_nxt;
r_pnt <= r_nxt;
end if;
end process pointer_update;
-- async pointer update --
w_nxt <= (others => '0') when (clear_i = '1') else std_ulogic_vector(unsigned(w_pnt) + 1) when (we = '1') else w_pnt;
r_nxt <= (others => '0') when (clear_i = '1') else std_ulogic_vector(unsigned(r_pnt) + 1) when (re = '1') else r_pnt;
-- Status ---------------------------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
-- more than 1 FIFO entries --
check_large:
if (fifo_depth_c > 1) generate
match <= '1' when (r_pnt(r_pnt'left-1 downto 0) = w_pnt(w_pnt'left-1 downto 0)) else '0';
full <= '1' when (r_pnt(r_pnt'left) /= w_pnt(w_pnt'left)) and (match = '1') else '0';
empty <= '1' when (r_pnt(r_pnt'left) = w_pnt(w_pnt'left)) and (match = '1') else '0';
diff <= std_ulogic_vector(unsigned(w_pnt) - unsigned(r_pnt));
half <= diff(diff'left-1) or full;
end generate;
-- just 1 FIFO entry --
check_small:
if (fifo_depth_c = 1) generate
match <= '1' when (r_pnt(0) = w_pnt(0)) else '0';
full <= not match;
empty <= match;
half <= full;
end generate;
free <= not full;
avail <= not empty;
-- Write Access (with Reset) --------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
memory_full_reset: -- cannot be mapped to memory primitives
if FULL_RESET generate
-- just 1 FIFO entry --
fifo_write_reset_small:
if (fifo_depth_c = 1) generate
write_reset_small: process(rstn_i, clk_i)
begin
if (rstn_i = '0') then
fifo_reg <= (others => '0');
elsif rising_edge(clk_i) then
if (we = '1') then
fifo_reg <= wdata_i;
end if;
end if;
end process write_reset_small;
end generate;
-- more than 1 FIFO entries --
fifo_write_reset_large:
if (fifo_depth_c > 1) generate
write_reset_large: process(rstn_i, clk_i)
begin
if (rstn_i = '0') then
fifo_mem <= (others => (others => '0'));
elsif rising_edge(clk_i) then
if (we = '1') then
fifo_mem(to_integer(unsigned(w_pnt(w_pnt'left-1 downto 0)))) <= wdata_i;
end if;
end if;
end process write_reset_large;
end generate;
end generate;
-- Write Access (without Reset) -----------------------------------------------------------
-- -------------------------------------------------------------------------------------------
memory_no_reset: -- no reset to infer memory primitives
if not FULL_RESET generate
-- just 1 FIFO entry --
fifo_write_noreset_small:
if (fifo_depth_c = 1) generate
write_small: process(clk_i)
begin
if rising_edge(clk_i) then
if (we = '1') then
fifo_reg <= wdata_i;
end if;
end if;
end process write_small;
end generate;
-- more than 1 FIFO entries --
fifo_write_noreset_large:
if (fifo_depth_c > 1) generate
write_large: process(clk_i)
begin
if rising_edge(clk_i) then
if (we = '1') then
fifo_mem(to_integer(unsigned(w_pnt(w_pnt'left-1 downto 0)))) <= wdata_i;
end if;
end if;
end process write_large;
end generate;
end generate;
-- Asynchronous Read Access ---------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
fifo_read_async:
if not FIFO_RSYNC generate
-- just 1 FIFO entry --
fifo_read_async_small:
if (fifo_depth_c = 1) generate
rdata_o <= fifo_reg;
end generate;
-- more than 1 FIFO entries --
fifo_read_async_large:
if (fifo_depth_c > 1) generate
async_r_pnt_reg: process(clk_i)
begin
if rising_edge(clk_i) then
r_pnt_ff <= r_nxt; -- individual read address register; allows mapping "async" FIFOs to memory primitives
end if;
end process async_r_pnt_reg;
rdata_o <= fifo_mem(to_integer(unsigned(r_pnt_ff(r_pnt_ff'left-1 downto 0))));
end generate;
-- status --
free_o <= free;
avail_o <= avail;
half_o <= half;
end generate;
-- Synchronous Read Access ----------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
fifo_read_sync:
if FIFO_RSYNC generate
-- just 1 FIFO entry --
fifo_read_sync_small:
if (fifo_depth_c = 1) generate
sync_read_small: process(clk_i)
begin
if rising_edge(clk_i) then
rdata_o <= fifo_reg;
end if;
end process sync_read_small;
end generate;
-- more than 1 FIFO entries --
fifo_read_sync_large:
if (fifo_depth_c > 1) generate
sync_read_large: process(clk_i)
begin
if rising_edge(clk_i) then
rdata_o <= fifo_mem(to_integer(unsigned(r_pnt(r_pnt'left-1 downto 0))));
end if;
end process sync_read_large;
end generate;
-- registered status --
sync_status: process(rstn_i, clk_i)
begin
if (rstn_i = '0') then
free_o <= '0';
avail_o <= '0';
half_o <= '0';
elsif rising_edge(clk_i) then
free_o <= free;
avail_o <= avail;
half_o <= half;
end if;
end process sync_status;
end generate;
end neorv32_fifo_rtl;