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[rtl] rework FIFO module (to allow inferring block RAM) (#754)
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@stnolting
stnolting authored Dec 19, 2023
2 parents 513f04b + 2dfd2ab commit a747612
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -30,6 +30,7 @@ mimpid = 0x01040312 -> Version 01.04.03.12 -> v1.4.3.12

| Date | Version | Comment | Link |
|:----:|:-------:|:--------|:----:|
| 19.12.2023 | 1.9.2.6 | rework FIFO component fixing problems with inferring block RAM | [#754](https://github.com/stnolting/neorv32/pull/754) |
| 11.12.2023 | 1.9.2.5 | clean-up software framework | [#752](https://github.com/stnolting/neorv32/pull/752) |
| 09.12.2023 | 1.9.2.4 | minor rtl code cleanups | [#747](https://github.com/stnolting/neorv32/pull/747) |
| 09.12.2023 | 1.9.2.3 | refine behavior of CPU's sleep state & signal | [#746](https://github.com/stnolting/neorv32/pull/746) |
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150 changes: 57 additions & 93 deletions rtl/core/neorv32_fifo.vhd
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@@ -1,5 +1,5 @@
-- #################################################################################################
-- # << NEORV32 - Generic Single-Clock FIFO >> #
-- # << NEORV32 - Generic Single-Clock FIFO Component >> #
-- # ********************************************************************************************* #
-- # BSD 3-Clause License #
-- # #
Expand Down Expand Up @@ -68,139 +68,103 @@ 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 --
type fifo_data_t is array (0 to fifo_depth_c-1) of std_ulogic_vector(FIFO_WIDTH-1 downto 0);
type fifo_t is record
we : std_ulogic; -- write enable
re : std_ulogic; -- read enable
w_pnt : std_ulogic_vector(index_size_f(fifo_depth_c) downto 0); -- write pointer
r_pnt : std_ulogic_vector(index_size_f(fifo_depth_c) downto 0); -- read pointer
data : fifo_data_t; -- fifo memory
match : std_ulogic;
empty : std_ulogic;
full : std_ulogic;
half : std_ulogic;
free : std_ulogic;
avail : std_ulogic;
end record;
signal fifo : fifo_t;

-- misc --
signal level_diff : std_ulogic_vector(index_size_f(fifo_depth_c) downto 0);
-- 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;

-- 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

-- 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 -------------------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
fifo.re <= re_i when (FIFO_SAFE = false) else (re_i and fifo.avail); -- SAFE = read only if data available
fifo.we <= we_i when (FIFO_SAFE = false) else (we_i and fifo.free); -- SAFE = write only if space left
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


-- FIFO Pointers --------------------------------------------------------------------------
-- Pointers -------------------------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
pointer_update: process(rstn_i, clk_i)
begin
if (rstn_i = '0') then
fifo.w_pnt <= (others => '0');
fifo.r_pnt <= (others => '0');
w_pnt <= (others => '0');
r_pnt <= (others => '0');
elsif rising_edge(clk_i) then
-- write port --
if (clear_i = '1') then
fifo.w_pnt <= (others => '0');
elsif (fifo.we = '1') then
fifo.w_pnt <= std_ulogic_vector(unsigned(fifo.w_pnt) + 1);
w_pnt <= (others => '0');
elsif (we = '1') then
w_pnt <= std_ulogic_vector(unsigned(w_pnt) + 1);
end if;
-- read port --
if (clear_i = '1') then
fifo.r_pnt <= (others => '0');
elsif (fifo.re = '1') then
fifo.r_pnt <= std_ulogic_vector(unsigned(fifo.r_pnt) + 1);
r_pnt <= (others => '0');
elsif (re = '1') then
r_pnt <= std_ulogic_vector(unsigned(r_pnt) + 1);
end if;
end if;
end process pointer_update;

check_large:
if (fifo_depth_c > 1) generate
fifo.match <= '1' when (fifo.r_pnt(fifo.r_pnt'left-1 downto 0) = fifo.w_pnt(fifo.w_pnt'left-1 downto 0)) else '0';
fifo.full <= '1' when (fifo.r_pnt(fifo.r_pnt'left) /= fifo.w_pnt(fifo.w_pnt'left)) and (fifo.match = '1') else '0';
fifo.empty <= '1' when (fifo.r_pnt(fifo.r_pnt'left) = fifo.w_pnt(fifo.w_pnt'left)) and (fifo.match = '1') else '0';
level_diff <= std_ulogic_vector(unsigned(fifo.w_pnt) - unsigned(fifo.r_pnt));
fifo.half <= level_diff(level_diff'left-1) or fifo.full;
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;

check_small:
if (fifo_depth_c = 1) generate
fifo.match <= '1' when (fifo.r_pnt(0) = fifo.w_pnt(0)) else '0';
fifo.full <= not fifo.match;
fifo.empty <= fifo.match;
fifo.half <= fifo.full;
match <= '1' when (r_pnt(0) = w_pnt(0)) else '0';
full <= not match;
empty <= match;
half <= full;
end generate;

fifo.free <= not fifo.full;
fifo.avail <= not fifo.empty;
free <= not full;
avail <= not empty;


-- FIFO Write -----------------------------------------------------------------------------
-- Write Data -----------------------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
fifo_memory: -- real FIFO memory (several entries)
if (fifo_depth_c > 1) generate
sync_read: process(clk_i)
begin
if rising_edge(clk_i) then -- no reset to infer block RAM
if (fifo.we = '1') then
fifo.data(to_integer(unsigned(fifo.w_pnt(fifo.w_pnt'left-1 downto 0)))) <= wdata_i;
end if;
end if;
end process sync_read;
end generate;

fifo_buffer: -- simple register (single entry)
if (fifo_depth_c = 1) generate
sync_read: process(rstn_i, clk_i)
begin
if (rstn_i = '0') then
fifo.data(0) <= (others => '0');
elsif rising_edge(clk_i) then
if (fifo.we = '1') then
fifo.data(0) <= wdata_i;
end if;
fifo_write: process(clk_i)
begin
if rising_edge(clk_i) then -- no reset to infer block RAM
if (we = '1') then
fifo_mem(to_integer(unsigned(w_pnt(w_pnt'left-1 downto 0)))) <= wdata_i;
end if;
end process sync_read;
end generate;
end if;
end process fifo_write;


-- FIFO Read ------------------------------------------------------------------------------
-- Read Data ------------------------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
fifo_read_async: -- asynchronous read
if (FIFO_RSYNC = false) generate
async_read: process(fifo)
begin
if (fifo_depth_c = 1) then
rdata_o <= fifo.data(0);
else
rdata_o <= fifo.data(to_integer(unsigned(fifo.r_pnt(fifo.r_pnt'left-1 downto 0))));
end if;
end process async_read;

if not FIFO_RSYNC generate
rdata_o <= fifo_mem(to_integer(unsigned(r_pnt(r_pnt'left-1 downto 0))));
-- status --
free_o <= fifo.free;
avail_o <= fifo.avail;
half_o <= fifo.half;
free_o <= free;
avail_o <= avail;
half_o <= half;
end generate;

fifo_read_sync: -- synchronous read
if (FIFO_RSYNC = true) generate
async_read: process(clk_i)
if FIFO_RSYNC generate
sync_read: process(clk_i)
begin
if rising_edge(clk_i) then
if (fifo_depth_c = 1) then
rdata_o <= fifo.data(0);
else
rdata_o <= fifo.data(to_integer(unsigned(fifo.r_pnt(fifo.r_pnt'left-1 downto 0))));
end if;
rdata_o <= fifo_mem(to_integer(unsigned(r_pnt(r_pnt'left-1 downto 0))));
end if;
end process async_read;

end process sync_read;
-- status --
sync_status_flags: process(rstn_i, clk_i)
begin
Expand All @@ -209,9 +173,9 @@ begin
avail_o <= '0';
half_o <= '0';
elsif rising_edge(clk_i) then
free_o <= fifo.free;
avail_o <= fifo.avail;
half_o <= fifo.half;
free_o <= free;
avail_o <= avail;
half_o <= half;
end if;
end process sync_status_flags;
end generate;
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2 changes: 1 addition & 1 deletion rtl/core/neorv32_package.vhd
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Expand Up @@ -56,7 +56,7 @@ package neorv32_package is

-- Architecture Constants -----------------------------------------------------------------
-- -------------------------------------------------------------------------------------------
constant hw_version_c : std_ulogic_vector(31 downto 0) := x"01090205"; -- hardware version
constant hw_version_c : std_ulogic_vector(31 downto 0) := x"01090206"; -- hardware version
constant archid_c : natural := 19; -- official RISC-V architecture ID
constant XLEN : natural := 32; -- native data path width

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