在Xilinx FPGA中，要实现FIFO的功能时，大部分时候会使用两种方法：
- FIFO Generator IP核
- XPM_FIFO原语
FIFO Generator IP核的优点是有图形化界面，配置参数非常直观；缺点是参数一旦固定，想要更改的化就只能重新generate IP核。
XPM_FIFO原语的优点就是参数配置方便。
对于两者，还有一个非常重要的区别。！！！大小端不一样！！！
当din的位宽和dout的位宽非对称时。举个栗子：当din的位宽为8bit，dout的位宽为32bit时。
FIFO Generator IP核按大端输出，即先写进去的数据放在高8bit
XPM_FIFO原语按小端输出，即先写进去的数据放在低8bit
下面为RTL设计文件和测试结果。
//-----------------------------------------------------------------------------
//
// Copyright (c) JoeJoe.
//
// Project : fifo_test
// Module : fifo_test.v
// Parent : None
// Children : None
//
// Description:
//
//
//
//
// Parameters:
//
//
//
//
// Local Parameters:
//
// Notes :
//
// Multicycle and False Paths
// Some exist, embedded within the submodules. See the submodule
// descriptions.
//
`timescale 1ns/1ps
module fifo_test (
input sclk
,input srst_n
);
//***************************************************************************
// Parameter definitions
//***************************************************************************
//***************************************************************************
// Reg declarations
//***************************************************************************
reg [2:0] wait_cnt;
reg wr_en;
reg [7:0] din;
wire rd_en;
wire prog_full;
wire full;
wire empty;
wire [31:0] dout;
reg xpm_wr_en;
reg [7:0] xpm_din;
wire xpm_rd_en;
wire xpm_prog_full;
wire xpm_full;
wire xpm_empty;
wire [31:0] xpm_dout;
//***************************************************************************
// Wire declarations
//***************************************************************************
//***************************************************************************
// Code
//***************************************************************************
// 等待XPM FIFO not busy
always @(posedge sclk) begin
if (srst_n == 1'b0) begin
wait_cnt <= 'd0;
end
else begin
if (wait_cnt == 'd7) begin
wait_cnt <= wait_cnt;
end
else begin
wait_cnt <= wait_cnt + 'd1;
end
end
end
// 非满就写
always @(posedge sclk) begin
if (srst_n == 1'b0) begin
wr_en <= 1'b0;
din <= 'd0;
end
else begin
if (prog_full == 1'b1) begin
wr_en <= 1'b0;
din <= 'd0;
end
else if (wait_cnt == 'd7) begin
wr_en <= 1'b1;
din <= din + 'd1;
end
else begin
wr_en <= 1'b0;
din <= 'd0;
end
end
end
// 非空就读
assign rd_en = ~empty;
// 非满就写
always @(posedge sclk) begin
if (srst_n == 1'b0) begin
xpm_wr_en <= 1'b0;
xpm_din <= 'd0;
end
else begin
if (xpm_prog_full == 1'b1) begin
xpm_wr_en <= 1'b0;
xpm_din <= 'd0;
end
else if (wait_cnt == 'd7) begin
xpm_wr_en <= 1'b1;
xpm_din <= din + 'd1;
end
else begin
xpm_wr_en <= 1'b0;
xpm_din <= 'd0;
end
end
end
// 非空就读
assign xpm_rd_en = ~xpm_empty;
fifo_generator_0 U_FIFO_GENERATOR_0 (
.clk ( sclk ) // input wire clk
,.srst ( ~srst_n ) // input wire srst
,.din ( din ) // input wire [7 : 0] din
,.wr_en ( wr_en ) // input wire wr_en
,.rd_en ( rd_en ) // input wire rd_en
,.dout ( dout ) // output wire [31 : 0] dout
,.full ( full ) // output wire full
,.empty ( empty ) // output wire empty
,.prog_full ( prog_full ) // output wire prog_full
);
xpm_fifo_sync #(
.DOUT_RESET_VALUE ( "0" ), // String
.ECC_MODE ( "no_ecc" ), // String
.FIFO_MEMORY_TYPE ( "block" ), // String
.FIFO_READ_LATENCY ( 0 ), // DECIMAL
.FIFO_WRITE_DEPTH ( 1024 ), // DECIMAL
.FULL_RESET_VALUE ( 0 ), // DECIMAL
.PROG_EMPTY_THRESH ( 10 ), // DECIMAL
.PROG_FULL_THRESH ( 500 ), // DECIMAL
.RD_DATA_COUNT_WIDTH( 1 ), // DECIMAL
.READ_DATA_WIDTH ( 32 ), // DECIMAL
.READ_MODE ( "fwft" ), // String
.SIM_ASSERT_CHK ( 0 ), // DECIMAL; 0=disable simulation messages, 1=enable simulation messages
.USE_ADV_FEATURES ( "0707" ), // String
.WAKEUP_TIME ( 0 ), // DECIMAL
.WRITE_DATA_WIDTH ( 8 ), // DECIMAL
.WR_DATA_COUNT_WIDTH( 1 ) // DECIMAL
)
U_XPM_FIFO_SYNC (
.almost_empty ( ), // 1-bit output: Almost Empty : When asserted, this signal indicates that
// only one more read can be performed before the FIFO goes to empty.
.almost_full ( ), // 1-bit output: Almost Full: When asserted, this signal indicates that
// only one more write can be performed before the FIFO is full.
.data_valid ( ), // 1-bit output: Read Data Valid: When asserted, this signal indicates
// that valid data is available on the output bus (dout ).
.dbiterr ( ), // 1-bit output: Double Bit Error: Indicates that the ECC decoder detected
// a double-bit error and data in the FIFO core is corrupted.
.dout (xpm_dout ), // READ_DATA_WIDTH-bit output: Read Data: The output data bus is driven
// when reading the FIFO.
.empty (xpm_empty ), // 1-bit output: Empty Flag: When asserted, this signal indicates that the
// FIFO is empty. Read requests are ignored when the FIFO is empty,
// initiating a read while empty is not destructive to the FIFO.
.full (xpm_full ), // 1-bit output: Full Flag: When asserted, this signal indicates that the
// FIFO is full. Write requests are ignored when the FIFO is full,
// initiating a write when the FIFO is full is not destructive to the
// contents of the FIFO.
.overflow ( ), // 1-bit output: Overflow: This signal indicates that a write request
// (wren) during the prior clock cycle was rejected, because the FIFO is
// full. Overflowing the FIFO is not destructive to the contents of the
// FIFO.
.prog_empty ( ), // 1-bit output: Programmable Empty: This signal is asserted when the
// number of words in the FIFO is less than or equal to the programmable
// empty threshold value. It is de-asserted when the number of words in
// the FIFO exceeds the programmable empty threshold value.
.prog_full (xpm_prog_full), // 1-bit output: Programmable Full: This signal is asserted when the
// number of words in the FIFO is greater than or equal to the
// programmable full threshold value. It is de-asserted when the number of
// words in the FIFO is less than the programmable full threshold value.
.rd_data_count ( ), // RD_DATA_COUNT_WIDTH-bit output: Read Data Count: This bus indicates the
// number of words read from the FIFO.
.rd_rst_busy ( ), // 1-bit output: Read Reset Busy: Active-High indicator that the FIFO read
// domain is currently in a reset state.
.sbiterr ( ), // 1-bit output: Single Bit Error: Indicates that the ECC decoder detected
// and fixed a single-bit error.
.underflow ( ), // 1-bit output: Underflow: Indicates that the read request (rd_en) during
// the previous clock cycle was rejected because the FIFO is empty. Under
// flowing the FIFO is not destructive to the FIFO.
.wr_ack ( ), // 1-bit output: Write Acknowledge: This signal indicates that a write
// request(wr_en) during the prior clock cycle is succeeded.
.wr_data_count ( ), // WR_DATA_COUNT_WIDTH-bit output: Write Data Count: This bus indicates
// the number of words written into the FIFO.
.wr_rst_busy ( ), // 1-bit output: Write Reset Busy: Active-High indicator that the FIFO
// write domain is currently in a reset state.
.din (xpm_din ), // WRITE_DATA_WIDTH-bit input: Write Data: The input data bus used when
// writing the FIFO.
.injectdbiterr (1'b0 ), // 1-bit input: Double Bit Error Injection: Injects a double bit error if
// the ECC feature is used on block RAMs or UltraRAM macros.
.injectsbiterr (1'b0 ), // 1-bit input: Single Bit Error Injection: Injects a single bit error if
// the ECC feature is used on block RAMs or UltraRAM macros.
.rd_en (xpm_rd_en ), // 1-bit input: Read Enable: If the FIFO is not empty, asserting this
// signal causes data(on dout) to be read from the FIFO. Must be held
// active-low when rd_rst_busy is active high.
.rst (~srst_n ), // 1-bit input: Reset: Must be synchronous to wr_clk. The clock(s) can be
// unstable at the time of applying reset, but reset must be released only
// after the clock(s) is/are stable.
.sleep (1'b0 ), // 1-bit input: Dynamic power saving- If sleep is High, the memory/fifo
// block is in power saving mode.
.wr_clk (sclk ), // 1-bit input: Write clock: Used for write operation. wr_clk must be a
// free running clock.
.wr_en (xpm_wr_en ) // 1-bit input: Write Enable: If the FIFO is not full, asserting this
// signal causes data(on din) to be written to the FIFO Must be held
// active-low when rst or wr_rst_busy or rd_rst_busy is active high
);
endmodule
当din的位宽和dout的位宽非对称时。举个栗子：当din的位宽为32bit，dout的位宽为8bit时。
FIFO Generator IP核 高8bit先输出，低8bit最后输出
XPM_FIFO原语 低8bit先输出，高8bit最后输出
下面为RTL设计文件和测试结果。
//-----------------------------------------------------------------------------
//
// Copyright (c) JoeJoe.
//
// Project : fifo_test
// Module : fifo_test.v
// Parent : None
// Children : None
//
// Description:
//
//
//
//
// Parameters:
//
//
//
//
// Local Parameters:
//
// Notes :
//
// Multicycle and False Paths
// Some exist, embedded within the submodules. See the submodule
// descriptions.
//
`timescale 1ns/1ps
module fifo_test (
input sclk
,input srst_n
);
//***************************************************************************
// Parameter definitions
//***************************************************************************
//***************************************************************************
// Reg declarations
//***************************************************************************
reg [2:0] wait_cnt;
reg wr_en;
reg [31:0] din;
wire rd_en;
wire prog_full;
wire full;
wire empty;
wire [7:0] dout;
reg xpm_wr_en;
reg [31:0] xpm_din;
wire xpm_rd_en;
wire xpm_prog_full;
wire xpm_full;
wire xpm_empty;
wire [7:0] xpm_dout;
//***************************************************************************
// Wire declarations
//***************************************************************************
//***************************************************************************
// Code
//***************************************************************************
// 等待XPM FIFO not busy
always @(posedge sclk) begin
if (srst_n == 1'b0) begin
wait_cnt <= 'd0;
end
else begin
if (wait_cnt == 'd7) begin
wait_cnt <= wait_cnt;
end
else begin
wait_cnt <= wait_cnt + 'd1;
end
end
end
// 非满就写
always @(posedge sclk) begin
if (srst_n == 1'b0) begin
wr_en <= 1'b0;
din <= 'd0;
end
else begin
if (prog_full == 1'b1) begin
wr_en <= 1'b0;
din <= din;
end
else if (wait_cnt == 'd7) begin
wr_en <= 1'b1;
din <= din + 'd1;
end
else begin
wr_en <= 1'b0;
din <= 'd0;
end
end
end
// 非空就读
assign rd_en = ~empty;
// 非满就写
always @(posedge sclk) begin
if (srst_n == 1'b0) begin
xpm_wr_en <= 1'b0;
xpm_din <= 'd0;
end
else begin
if (xpm_prog_full == 1'b1) begin
xpm_wr_en <= 1'b0;
xpm_din <= xpm_din;
end
else if (wait_cnt == 'd7) begin
xpm_wr_en <= 1'b1;
xpm_din <= xpm_din + 'd1;
end
else begin
xpm_wr_en <= 1'b0;
xpm_din <= 'd0;
end
end
end
// 非空就读
assign xpm_rd_en = ~xpm_empty;
// fifo_generator_0 U_FIFO_GENERATOR_0 (
// .clk ( sclk ) // input wire clk
// ,.srst ( ~srst_n ) // input wire srst
// ,.din ( din ) // input wire [7 : 0] din
// ,.wr_en ( wr_en ) // input wire wr_en
// ,.rd_en ( rd_en ) // input wire rd_en
// ,.dout ( dout ) // output wire [31 : 0] dout
// ,.full ( full ) // output wire full
// ,.empty ( empty ) // output wire empty
// ,.prog_full ( prog_full ) // output wire prog_full
// );
fifo_generator_1 U_FIFO_GENERATOR_1 (
.clk ( sclk ) // input wire clk
,.srst ( ~srst_n ) // input wire srst
,.din ( din ) // input wire [31 : 0] din
,.wr_en ( wr_en ) // input wire wr_en
,.rd_en ( rd_en ) // input wire rd_en
,.dout ( dout ) // output wire [7 : 0] dout
,.full ( full ) // output wire full
,.empty ( empty ) // output wire empty
,.prog_full ( prog_full ) // output wire prog_full
);
xpm_fifo_sync #(
.DOUT_RESET_VALUE ( "0" ), // String
.ECC_MODE ( "no_ecc" ), // String
.FIFO_MEMORY_TYPE ( "block" ), // String
.FIFO_READ_LATENCY ( 0 ), // DECIMAL
.FIFO_WRITE_DEPTH ( 256 ), // DECIMAL
.FULL_RESET_VALUE ( 0 ), // DECIMAL
.PROG_EMPTY_THRESH ( 10 ), // DECIMAL
.PROG_FULL_THRESH ( 125 ), // DECIMAL
.RD_DATA_COUNT_WIDTH( 1 ), // DECIMAL
.READ_DATA_WIDTH ( 8 ), // DECIMAL
.READ_MODE ( "fwft" ), // String
.SIM_ASSERT_CHK ( 0 ), // DECIMAL; 0=disable simulation messages, 1=enable simulation messages
.USE_ADV_FEATURES ( "0707" ), // String
.WAKEUP_TIME ( 0 ), // DECIMAL
.WRITE_DATA_WIDTH ( 32 ), // DECIMAL
.WR_DATA_COUNT_WIDTH( 1 ) // DECIMAL
)
U_XPM_FIFO_SYNC (
.almost_empty ( ), // 1-bit output: Almost Empty : When asserted, this signal indicates that
// only one more read can be performed before the FIFO goes to empty.
.almost_full ( ), // 1-bit output: Almost Full: When asserted, this signal indicates that
// only one more write can be performed before the FIFO is full.
.data_valid ( ), // 1-bit output: Read Data Valid: When asserted, this signal indicates
// that valid data is available on the output bus (dout ).
.dbiterr ( ), // 1-bit output: Double Bit Error: Indicates that the ECC decoder detected
// a double-bit error and data in the FIFO core is corrupted.
.dout (xpm_dout ), // READ_DATA_WIDTH-bit output: Read Data: The output data bus is driven
// when reading the FIFO.
.empty (xpm_empty ), // 1-bit output: Empty Flag: When asserted, this signal indicates that the
// FIFO is empty. Read requests are ignored when the FIFO is empty,
// initiating a read while empty is not destructive to the FIFO.
.full (xpm_full ), // 1-bit output: Full Flag: When asserted, this signal indicates that the
// FIFO is full. Write requests are ignored when the FIFO is full,
// initiating a write when the FIFO is full is not destructive to the
// contents of the FIFO.
.overflow ( ), // 1-bit output: Overflow: This signal indicates that a write request
// (wren) during the prior clock cycle was rejected, because the FIFO is
// full. Overflowing the FIFO is not destructive to the contents of the
// FIFO.
.prog_empty ( ), // 1-bit output: Programmable Empty: This signal is asserted when the
// number of words in the FIFO is less than or equal to the programmable
// empty threshold value. It is de-asserted when the number of words in
// the FIFO exceeds the programmable empty threshold value.
.prog_full (xpm_prog_full), // 1-bit output: Programmable Full: This signal is asserted when the
// number of words in the FIFO is greater than or equal to the
// programmable full threshold value. It is de-asserted when the number of
// words in the FIFO is less than the programmable full threshold value.
.rd_data_count ( ), // RD_DATA_COUNT_WIDTH-bit output: Read Data Count: This bus indicates the
// number of words read from the FIFO.
.rd_rst_busy ( ), // 1-bit output: Read Reset Busy: Active-High indicator that the FIFO read
// domain is currently in a reset state.
.sbiterr ( ), // 1-bit output: Single Bit Error: Indicates that the ECC decoder detected
// and fixed a single-bit error.
.underflow ( ), // 1-bit output: Underflow: Indicates that the read request (rd_en) during
// the previous clock cycle was rejected because the FIFO is empty. Under
// flowing the FIFO is not destructive to the FIFO.
.wr_ack ( ), // 1-bit output: Write Acknowledge: This signal indicates that a write
// request(wr_en) during the prior clock cycle is succeeded.
.wr_data_count ( ), // WR_DATA_COUNT_WIDTH-bit output: Write Data Count: This bus indicates
// the number of words written into the FIFO.
.wr_rst_busy ( ), // 1-bit output: Write Reset Busy: Active-High indicator that the FIFO
// write domain is currently in a reset state.
.din (xpm_din ), // WRITE_DATA_WIDTH-bit input: Write Data: The input data bus used when
// writing the FIFO.
.injectdbiterr (1'b0 ), // 1-bit input: Double Bit Error Injection: Injects a double bit error if
// the ECC feature is used on block RAMs or UltraRAM macros.
.injectsbiterr (1'b0 ), // 1-bit input: Single Bit Error Injection: Injects a single bit error if
// the ECC feature is used on block RAMs or UltraRAM macros.
.rd_en (xpm_rd_en ), // 1-bit input: Read Enable: If the FIFO is not empty, asserting this
// signal causes data(on dout) to be read from the FIFO. Must be held
// active-low when rd_rst_busy is active high.
.rst (~srst_n ), // 1-bit input: Reset: Must be synchronous to wr_clk. The clock(s) can be
// unstable at the time of applying reset, but reset must be released only
// after the clock(s) is/are stable.
.sleep (1'b0 ), // 1-bit input: Dynamic power saving- If sleep is High, the memory/fifo
// block is in power saving mode.
.wr_clk (sclk ), // 1-bit input: Write clock: Used for write operation. wr_clk must be a
// free running clock.
.wr_en (xpm_wr_en ) // 1-bit input: Write Enable: If the FIFO is not full, asserting this
// signal causes data(on din) to be written to the FIFO Must be held
// active-low when rst or wr_rst_busy or rd_rst_busy is active high
);
endmodule
参考文档如下：《FIFO Generator v13.2 Product Guide》(PG057)
FIFO Generator IP，小位宽写，大位宽读，大端。
FIFO Generator IP，大位宽写，小位宽读。
疑问：XPM_FIFO为什么不可以设置大小端，以及为什么不和FIFO Generator IP统一？？？
