util_axis_fifo: Add room and level outputs

Add a room output on the input side that reports how many free entries the
FIFO has and a level output on the output side that reports how many valid
entries are in the FIFO.

Note that the level output is only accurate if the output of the FIFO is not
registered, otherwise it might be off by one.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

library/util_axis_fifo/address_gray.v

@@ -42,13 +42,15 @@ module fifo_address_gray (
 	input m_axis_ready,
 	output reg m_axis_valid,
 	output [C_ADDRESS_WIDTH-1:0] m_axis_raddr_next,
+	output reg [C_ADDRESS_WIDTH:0] m_axis_level,
 
 	input s_axis_aclk,
 	input s_axis_aresetn,
 	output reg s_axis_ready,
 	input s_axis_valid,
 	output reg s_axis_empty,
-	output [C_ADDRESS_WIDTH-1:0] s_axis_waddr
+	output [C_ADDRESS_WIDTH-1:0] s_axis_waddr,
+	output reg [C_ADDRESS_WIDTH:0] s_axis_room
 );
 
 parameter C_ADDRESS_WIDTH = 4;

library/util_axis_fifo/address_gray_pipelined.v

@@ -43,13 +43,15 @@ module fifo_address_gray_pipelined (
 	output reg m_axis_valid,
 	output [C_ADDRESS_WIDTH-1:0] m_axis_raddr_next,
 	output [C_ADDRESS_WIDTH-1:0] m_axis_raddr,
+	output reg [C_ADDRESS_WIDTH:0] m_axis_level,
 
 	input s_axis_aclk,
 	input s_axis_aresetn,
 	output reg s_axis_ready,
 	input s_axis_valid,
 	output reg s_axis_empty,
-	output [C_ADDRESS_WIDTH-1:0] s_axis_waddr
+	output [C_ADDRESS_WIDTH-1:0] s_axis_waddr,
+	output reg [C_ADDRESS_WIDTH:0] s_axis_room
 );
 
 parameter C_ADDRESS_WIDTH = 4;
@@ -127,19 +129,23 @@ begin
 	if (s_axis_aresetn == 1'b0) begin
 		s_axis_ready <= 1'b1;
 		s_axis_empty <= 1'b1;
+		s_axis_room <= 2**C_ADDRESS_WIDTH;
 	end else begin
 		s_axis_ready <= (_s_axis_raddr[C_ADDRESS_WIDTH] == _s_axis_waddr_next[C_ADDRESS_WIDTH] ||
 			_s_axis_raddr[C_ADDRESS_WIDTH-1:0] != _s_axis_waddr_next[C_ADDRESS_WIDTH-1:0]);
 		s_axis_empty <= _s_axis_raddr == _s_axis_waddr_next;
+		s_axis_room <= _s_axis_raddr - _s_axis_waddr_next + 2**C_ADDRESS_WIDTH;
 	end
 end
 
 always @(posedge m_axis_aclk)
 begin
-	if (s_axis_aresetn == 1'b0)
+	if (s_axis_aresetn == 1'b0) begin
 		m_axis_valid <= 1'b0;
-	else begin
+		m_axis_level <= 'h00;
+	end else begin
 		m_axis_valid <= _m_axis_waddr != _m_axis_raddr_next;
+		m_axis_level <= _m_axis_waddr - _m_axis_raddr_next;
 	end
 end
 

library/util_axis_fifo/address_sync.v

@@ -44,18 +44,24 @@ module fifo_address_sync (
 	output reg m_axis_valid,
 	output reg  [C_ADDRESS_WIDTH-1:0] m_axis_raddr,
 	output reg [C_ADDRESS_WIDTH-1:0] m_axis_raddr_next,
+	output [C_ADDRESS_WIDTH:0] m_axis_level,
 
 	output reg s_axis_ready,
 	input s_axis_valid,
 	output reg s_axis_empty,
-	output reg [C_ADDRESS_WIDTH-1:0] s_axis_waddr
+	output reg [C_ADDRESS_WIDTH-1:0] s_axis_waddr,
+	output [C_ADDRESS_WIDTH:0] s_axis_room
 );
 
 parameter C_ADDRESS_WIDTH = 4;
 
-reg [C_ADDRESS_WIDTH:0] level;
+reg [C_ADDRESS_WIDTH:0] room = 2**C_ADDRESS_WIDTH;
+reg [C_ADDRESS_WIDTH:0] level = 'h00;
 reg [C_ADDRESS_WIDTH:0] level_next;
 
+assign s_axis_room = room;
+assign m_axis_level = level;
+
 wire read = m_axis_ready & m_axis_valid;
 wire write = s_axis_ready & s_axis_valid;
 
@@ -94,8 +100,12 @@ begin
 	if (resetn == 1'b0) begin
 		m_axis_valid <= 1'b0;
 		s_axis_ready <= 1'b0;
+		level <= 'h00;
+		room <= 2**C_ADDRESS_WIDTH;
+		s_axis_empty <= 'h00;
 	end else begin
 		level <= level_next;
+		room <= 2**C_ADDRESS_WIDTH - level_next;
 		m_axis_valid <= level_next != 0;
 		s_axis_ready <= level_next != 2**C_ADDRESS_WIDTH;
 		s_axis_empty <= level_next == 0;

library/util_axis_fifo/util_axis_fifo.v

@@ -42,13 +42,15 @@ module util_axis_fifo (
 	input m_axis_ready,
 	output m_axis_valid,
 	output [C_DATA_WIDTH-1:0] m_axis_data,
+	output [C_ADDRESS_WIDTH:0] m_axis_level,
 
 	input s_axis_aclk,
 	input s_axis_aresetn,
 	output s_axis_ready,
 	input s_axis_valid,
 	input [C_DATA_WIDTH-1:0] s_axis_data,
-	output s_axis_empty
+	output s_axis_empty,
+	output [C_ADDRESS_WIDTH:0] s_axis_room
 );
 
 parameter C_DATA_WIDTH = 64;
@@ -86,8 +88,10 @@ sync_bits #(
 );
 
 assign m_axis_valid = m_axis_raddr != m_axis_waddr;
+assign m_axis_level = m_axis_valid;
 assign s_axis_ready = s_axis_raddr == s_axis_waddr;
-assign s_axis_empty = s_axis_raddr == s_axis_waddr;
+assign s_axis_empty = s_axis_ready;
+assign s_axis_room = s_axis_ready;
 
 always @(posedge s_axis_aclk) begin
 	if (s_axis_ready)
@@ -131,17 +135,18 @@ fifo_address_gray_pipelined #(
 ) i_address_gray (
 	.m_axis_aclk(m_axis_aclk),
 	.m_axis_aresetn(m_axis_aresetn),
-
 	.m_axis_ready(_m_axis_ready),
 	.m_axis_valid(_m_axis_valid),
 	.m_axis_raddr(m_axis_raddr),
+	.m_axis_level(m_axis_level),
 
 	.s_axis_aclk(s_axis_aclk),
 	.s_axis_aresetn(s_axis_aresetn),
 	.s_axis_ready(s_axis_ready),
 	.s_axis_valid(s_axis_valid),
 	.s_axis_empty(s_axis_empty),
-	.s_axis_waddr(s_axis_waddr)
+	.s_axis_waddr(s_axis_waddr),
+	.s_axis_room(s_axis_room)
 );
 
 end else begin
@@ -151,15 +156,16 @@ fifo_address_sync #(
 ) i_address_sync (
 	.clk(m_axis_aclk),
 	.resetn(m_axis_aresetn),
-
 	.m_axis_ready(_m_axis_ready),
 	.m_axis_valid(_m_axis_valid),
 	.m_axis_raddr(m_axis_raddr),
+	.m_axis_level(m_axis_level),
 
 	.s_axis_ready(s_axis_ready),
 	.s_axis_valid(s_axis_valid),
 	.s_axis_empty(s_axis_empty),
-	.s_axis_waddr(s_axis_waddr)
+	.s_axis_waddr(s_axis_waddr),
+	.s_axis_room(s_axis_room)
 );
 
 end