米联客-XILINX-H3_CZ08_7100] FPGA_AXI总线入门连载-04AXI4 总线 axi-full-master

本帖最后由 FPGA课程于 2024-10-12 16:22 编辑

软件版本：VIVADO2021.1
操作系统：WIN10 64bit
硬件平台：适用 XILINX A7/K7/Z7/ZU/KU 系列 FPGA
实验平台：米联客-MLK-H3-CZ08-7100开发板
板卡获取平台：https://milianke.tmall.com/
登录“米联客”FPGA社区 http://www.uisrc.com 视频课程、答疑解惑！

1概述

使用XILINX 的软件工具VIVADO以及XILINX的7代以上的FPGA或者SOC掌握AXI-4总线结束，并且可以灵活使用AXI-4总线技术完成数据的交换，可以让我们在构建强大的FPGA内部总线数据互联通信方面取得高效、高速、标准化的优势。

关于AXI4总线协议的部分介绍请阅读“01AXI4总线axi-lite-slave”。

本文实验目的：

1:掌握基于VIVADO工具产生AXI协议模板

2:掌握通过VIVADO工具产生AXI-full-master代码

3:理解AXI-full-master中自定义寄存器的地址分配

4:掌握通过VIVADO封装AXI-full-slave图形化IP

5:通过仿真验证AXI-full-master IP的工作是否正常。

2创建axi4-full-master总线接口IP

新建fpga工程，过程省略

新建完成工程后，单击菜单栏Tools->Create and Package New IP，开始创建一个AXI4-Full接口总线IP

选择使用vivado自带的AXI总线模板创建一个AXI4-FULL接口IP

设置IP的名字为maxi_full

模板支持3种协议，分别是AXI4-Full ，AXI4-Lite ，AXI4-Stream，这选择Full；总线包括Master和Slave两种模式，这里选择Master模式

这里选择Verify Peripheral IP using AXI4 VIP可以对AXI4-Lite快速验证

单击Finish后展开VIVADO自动产生的demo，单击Block Design的工程，可以看到如下2个IP。其中maxi_full_0就是我们自定义的IP，另外一个slave_0是用来验证maxi_full_0正确性。

采用默认地址分配即可

继续再看代码看看里面有什么东西

路径uisrc/03_ip/ maxi_full_1.0/hdl路径下的maxi_full_v1_0_M00_AXI.v就是我们的源码。另外一个maxi_full_v1_0.v是软件产生了一个接口文件，如果我们自己定义IP可有可无。

3程序分析

axi总线信号的关键无非是地址和数据，而写地址的有效取决于AXI_AWVALID和AXI_AWREADY，写数据的有效取决于S_AXI_WVALID和S_AXI_WREADY。同理，读地址的有效取决于AXI_ARVALID和AXI_ARREADY，读数据的有效取决于S_AXI_RVALID和S_AXI_RREADY。所以以下代码的阅读分析注意也是围绕以上4个信号的有效时序。

以下程序我们把关键信号的代码拆分阅读

1:产生初始化信号

//Generate a pulse to initiate AXI transaction.
always @(posedge M_AXI_ACLK)
begin
// Initiates AXI transaction delay
if (M_AXI_ARESETN == 0 )
begin
init_txn_ff <= 1'b0;
init_txn_ff2 <= 1'b0;
end
else
begin
init_txn_ff <= INIT_AXI_TXN;
init_txn_ff2 <= init_txn_ff;
end
end

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2:axi-full-master的axi_awvalid

当（~axi_awvalid && start_single_burst_write）==1条件满足，开始一次写传输，设置axi_awvalid有效。

always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 )
begin
axi_awvalid <= 1'b0;
end
// If previously not valid , start next transaction
else if (~axi_awvalid && start_single_burst_write)
begin
axi_awvalid <= 1'b1;
end
/* Once asserted, VALIDs cannot be deasserted, so axi_awvalid
must wait until transaction is accepted */
else if (M_AXI_AWREADY && axi_awvalid)
begin
axi_awvalid <= 1'b0;
end
else
axi_awvalid <= axi_awvalid;
end

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3:axi-full-slave的axi_awaddr

写通道地址每当M_AXI_AWREADY && axi_awvalid地址加1

// Next address after AWREADY indicates previous address acceptance
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
begin
axi_awaddr <= 'b0;
end
else if (M_AXI_AWREADY && axi_awvalid)
begin
axi_awaddr <= axi_awaddr + burst_size_bytes;
end
else
axi_awaddr <= axi_awaddr;
end

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4:axi-full-master的axi_wvalid

设置axi_wvalid <= 1'b1开始写数据。wnext信号有效代码axi_full_master写数据有效。

assign wnext = M_AXI_WREADY & axi_wvalid;
// WVALID logic, similar to the axi_awvalid always block above
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 )
begin
axi_wvalid <= 1'b0;
end
// If previously not valid, start next transaction
else if (~axi_wvalid && start_single_burst_write)
begin
axi_wvalid <= 1'b1;
end
/* If WREADY and too many writes, throttle WVALID
Once asserted, VALIDs cannot be deasserted, so WVALID
must wait until burst is complete with WLAST */
else if (wnext && axi_wlast)
axi_wvalid <= 1'b0;
else
axi_wvalid <= axi_wvalid;
end

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5:axi-full-master的axi_master_last

axi_master_last信号，当条件满足(((write_index == C_M_AXI_BURST_LEN-2 && C_M_AXI_BURST_LEN >= 2) && wnext) || (C_M_AXI_BURST_LEN == 1 ))==1的时候，axi_wlast <= 1'b1。这是VIVADO自带的模板，但是这里有个bug，那就是必须确保slave可以连续接收数据，假设发送last的时候wnext==0，这样就不能把最后一个数据正确写入到slave中了。

//WLAST generation on the MSB of a counter underflow
// WVALID logic, similar to the axi_awvalid always block above
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 )
begin
axi_wlast <= 1'b0;
end
// axi_wlast is asserted when the write index
// count reaches the penultimate count to synchronize
// with the last write data when write_index is b1111
// else if (&(write_index[C_TRANSACTIONS_NUM-1:1])&& ~write_index[0] && wnext)
else if (((write_index == C_M_AXI_BURST_LEN-2 && C_M_AXI_BURST_LEN >= 2) && wnext) || (C_M_AXI_BURST_LEN == 1 ))
begin
axi_wlast <= 1'b1;
end
// Deassrt axi_wlast when the last write data has been
// accepted by the slave with a valid response
else if (wnext)
axi_wlast <= 1'b0;
else if (axi_wlast && C_M_AXI_BURST_LEN == 1)
axi_wlast <= 1'b0;
else
axi_wlast <= axi_wlast;
end

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删除以上代码，并且添加以下代码：

wire wlast=(write_index==C_M_AXI_BURST_LEN-1)&&wnext;
reg wlast_r1 = 1'b0;
always @(posedge M_AXI_ACLK)
wlast_r <= wlast;
assign axi_wlast = (wlast_r==1'b0)&&(wlast==1'b1);

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另外需要修改reg axi_wlast；为wire axi_wlast；

这样就可以确保发送wlast的时候数据肯定是有效的。

6:写次数记录write_index计数器

/* Burst length counter. Uses extra counter register bit to indicate terminal
count to reduce decode logic */
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 || start_single_burst_write == 1'b1)
begin
write_index <= 0;
end
else if (wnext && (write_index != C_M_AXI_BURST_LEN-1))
begin
write_index <= write_index + 1;
end
else
write_index <= write_index;
end

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7:axi-full-master的axi_wdata

axi_full_master写数据计数写数据

/* Write Data Generator
Data pattern is only a simple incrementing count from 0 for each burst */
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
axi_wdata <= 'b1;
//else if (wnext && axi_wlast)
// axi_wdata <= 'b0;
else if (wnext)
axi_wdata <= axi_wdata + 1;
else
axi_wdata <= axi_wdata;
end

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8:axi-full-master的axi_bready

设置axi_bready信号

always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 )
begin
axi_bready <= 1'b0;
end
// accept/acknowledge bresp with axi_bready by the master
// when M_AXI_BVALID is asserted by slave
else if (M_AXI_BVALID && ~axi_bready)
begin
axi_bready <= 1'b1;
end
// deassert after one clock cycle
else if (axi_bready)
begin
axi_bready <= 1'b0;
end
// retain the previous value
else
axi_bready <= axi_bready;
end

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9:axi-full-slave的axi_arvalid

Axi_full_master读通道的分析非常类似，代码是对称的。

当（~axi_arvalid && start_single_burst_read）==1条件满足，开始一次写传输，设置axi_arvalid有效。

always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 )
begin
axi_arvalid <= 1'b0;
end
// If previously not valid , start next transaction
else if (~axi_arvalid && start_single_burst_read)
begin
axi_arvalid <= 1'b1;
end
else if (M_AXI_ARREADY && axi_arvalid)
begin
axi_arvalid <= 1'b0;
end
else
axi_arvalid <= axi_arvalid;
end

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10:axi-full-slave的axi_araddr

读地址计算

// Next address after ARREADY indicates previous address acceptance
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
begin
axi_araddr <= 'b0;
end
else if (M_AXI_ARREADY && axi_arvalid)
begin
axi_araddr <= axi_araddr + burst_size_bytes;
end
else
axi_araddr <= axi_araddr;
end

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11:axi-full-master的axi_rready

读数据准备好

/* The Read Data channel returns the results of the read request
In this example the data checker is always able to accept
more data, so no need to throttle the RREADY signal */
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 )
begin
axi_rready <= 1'b0;
end
// accept/acknowledge rdata/rresp with axi_rready by the master
// when M_AXI_RVALID is asserted by slave
else if (M_AXI_RVALID)
begin
if (M_AXI_RLAST && axi_rready)
begin
axi_rready <= 1'b0;
end
else
begin
axi_rready <= 1'b1;
end
end
// retain the previous value
end

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12:读次数记录read_index计数器

读数据索引计数

assign rnext = M_AXI_RVALID && axi_rready;
// Burst length counter. Uses extra counter register bit to indicate
// terminal count to reduce decode logic
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1 || start_single_burst_read)
begin
read_index <= 0;
end
else if (rnext && (read_index != C_M_AXI_BURST_LEN-1))
begin
read_index <= read_index + 1;
end
else
read_index <= read_index;
end

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13:产生对比数据expected_rdata

数据expected_rdata用于和读出的M_AXI_RDATA进行对比以此验证数据的正确性。

//Generate expected read data to check against actual read data
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)// || M_AXI_RLAST)
expected_rdata <= 'b1;
else if (M_AXI_RVALID && axi_rready)
expected_rdata <= expected_rdata + 1;
else
expected_rdata <= expected_rdata;
end

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14:比对数据正确性

读写数据比较

//Check received read data against data generator
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
begin
read_mismatch <= 1'b0;
end
//Only check data when RVALID is active
else if (rnext && (M_AXI_RDATA != expected_rdata))
begin
read_mismatch <= 1'b1;
end
else
read_mismatch <= 1'b0;
end

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15:读写状态机

读写状态机源码

begin
mst_exec_state <= INIT_READ;//
end
else
begin
mst_exec_state <= INIT_WRITE;
if (~axi_awvalid && ~start_single_burst_write && ~burst_write_active)
begin
start_single_burst_write <= 1'b1;
end
else
begin
start_single_burst_write <= 1'b0; //Negate to generate a pulse
end
end
INIT_READ:
// This state is responsible to issue start_single_read pulse to
// initiate a read transaction. Read transactions will be
// issued until burst_read_active signal is asserted.
// read controller
if (reads_done)
begin
mst_exec_state <= INIT_COMPARE;
end
else
begin
mst_exec_state <= INIT_READ;
if (~axi_arvalid && ~burst_read_active && ~start_single_burst_read)
begin
start_single_burst_read <= 1'b1;
end
else
begin
start_single_burst_read <= 1'b0; //Negate to generate a pulse
end
end
INIT_COMPARE:
// This state is responsible to issue the state of comparison
// of written data with the read data. If no error flags are set,
// compare_done signal will be asseted to indicate success.
//if (~error_reg)
begin
ERROR <= error_reg;
mst_exec_state <= IDLE;
compare_done <= 1'b1;
end
default :
begin
mst_exec_state <= IDLE;
end
endcase
end
end //MASTER_EXECUTION_PROC

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整理成流程图，更加容易理解：

16:正在写burst_write_active

burst_write_active代表正在写操作

always @(posedge M_AXI_ACLK)
begin
if(M_AXI_ARESETN==0||init_txn_pulse==1'b1)
burst_write_active<=1'b0;
//The burst_write_active is asserted when a write burst transaction is initiated
else if (start_single_burst_write)
burst_write_active <= 1'b1;
else if (M_AXI_BVALID && axi_bready)
burst_write_active <= 0;
end

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17:写完成writes_done

写数据完成writes_done信号

always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
writes_done <= 1'b0;
//The writes_done should be associated with a bready response
//else if (M_AXI_BVALID && axi_bready && (write_burst_counter == {(C_NO_BURSTS_REQ-1){1}}) && axi_wlast)
else if (M_AXI_BVALID && (write_burst_counter[C_NO_BURSTS_REQ]) && axi_bready)
writes_done <= 1'b1;
else
writes_done <= writes_done;
end

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18:正在读burst_read_active

读burst_read_active代表正在读数据

// burst_read_active signal is asserted when there is a burst write transaction
// is initiated by the assertion of start_single_burst_write. start_single_burst_read
// signal remains asserted until the burst read is accepted by the master
always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
burst_read_active <= 1'b0;
//The burst_write_active is asserted when a write burst transaction is initiated
else if (start_single_burst_read)
burst_read_active <= 1'b1;
else if (M_AXI_RVALID && axi_rready && M_AXI_RLAST)
burst_read_active <= 0;
end

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19:读完成reads_done

读数据完成reads_done信号

always @(posedge M_AXI_ACLK)
begin
if (M_AXI_ARESETN == 0 || init_txn_pulse == 1'b1)
reads_done <= 1'b0;
//The reads_done should be associated with a rready response
//else if (M_AXI_BVALID && axi_bready && (write_burst_counter == {(C_NO_BURSTS_REQ-1){1}}) && axi_wlast)
else if (M_AXI_RVALID && axi_rready && (read_index == C_M_AXI_BURST_LEN-1) && (read_burst_counter[C_NO_BURSTS_REQ]))
reads_done <= 1'b1;
else
reads_done <= reads_done;
end

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20:IP的更新

由于修改了代码，需要先更新IP状态，完成IP更新

4实验结果

仿真结果

一次axi4写操作burst lenth=16如下图所示，由于WREADY信号不是连续的，所以可以传输效率不是最高的

一共进行64次burst共计写了1024个32bit数据

一次读操作的burst lenth也是16如下图，但是可以看到读数据时连续的，所以效率最高

一共进行64次burst共计读了1024个32bit数据

可以看到读出的数据RDATA和expected_rdata一致，所以代码正确。

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