米联客-XILINX-H3_CZ08_7100] FPGA_AXI总线入门连载-03AXI4 总线 axi-full-slave

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-slave代码

3:理解AXI-full-slave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-slave IP的工作是否正常。

2创建axi4-full-slave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saxi_full

模板支持3种协议，分别是AXI4-Full ，AXI4-Lite ，AXI4-Stream，这里选择full;

总线包括Master和Slave两种模式，这里选择Slave模式

这里选择Verify Peripheral IP using AXI4 VIP 可以对AXI4-FULL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saxi_full_0就是我们自定义的IP，另外一个master_0是用来读写我们自定义的saxi_full_0，以此验证我们的IP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/ saxi_full_1.0/hdl 路径下的 saxi_full_v1_0_S00_AXI.v 就是我们的源码。另外一个 saxi_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
1:axi-full-slave的axi_awready

// axi_awready is asserted for one S_AXI_ACLK clock cycle when both
// S_AXI_AWVALID and S_AXI_WVALID are asserted. axi_awready is
// de-asserted when reset is low.
always @( posedge S_AXI_ACLK )
begin
if ( S_AXI_ARESETN == 1'b0 )
begin
axi_awready <= 1'b0;
axi_awv_awr_flag <= 1'b0;
end
else
begin
if (~axi_awready && S_AXI_AWVALID && ~axi_awv_awr_flag && ~axi_arv_arr_flag)
begin
// slave is ready to accept an address and
// associated control signals
axi_awready <= 1'b1;
axi_awv_awr_flag <= 1'b1;
// used for generation of bresp() and bvalid
end
else if (S_AXI_WLAST && axi_wready)
// preparing to accept next address after current write burst tx completion
begin
axi_awv_awr_flag <= 1'b0;
end
else
begin
axi_awready <= 1'b0;
end
end
end

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2:axi-full-slave的axi_awaddr

AXI的burst模式包括3种：

1:fixed burst这种模式下地址都是相同的

2: incremental burst这种模式下地址递增

3: Wrapping burst 这只模式下地址达到设置的最大地址边界后返回原来的地址。

本文demo中以下三种模式的具体代码如下：

//This process is used to latch the address when both
//S_AXI_ARVALID and S_AXI_RVALID are valid.
always @( posedge S_AXI_ACLK )
begin
if ( S_AXI_ARESETN == 1'b0 )
begin
axi_araddr <= 0;
axi_arlen_cntr <= 0;
axi_arburst <= 0;
axi_arlen <= 0;
axi_rlast <= 1'b0;
axi_ruser <= 0;
end
else
begin
if (~axi_arready && S_AXI_ARVALID && ~axi_arv_arr_flag)
begin
// address latching
axi_araddr <= S_AXI_ARADDR[C_S_AXI_ADDR_WIDTH - 1:0];
axi_arburst <= S_AXI_ARBURST;
axi_arlen <= S_AXI_ARLEN;
// start address of transfer
axi_arlen_cntr <= 0;
axi_rlast <= 1'b0;
end
else if((axi_arlen_cntr <= axi_arlen) && axi_rvalid && S_AXI_RREADY)
begin
axi_arlen_cntr <= axi_arlen_cntr + 1;
axi_rlast <= 1'b0;
case (axi_arburst)
2'b00: // fixed burst
// The read address for all the beats in the transaction are fixed
begin
axi_araddr <= axi_araddr;
//for arsize = 4 bytes (010)
end
2'b01: //incremental burst
// The read address for all the beats in the transaction are increments by awsize
begin
axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;
//araddr aligned to 4 byte boundary
axi_araddr[ADDR_LSB-1:0] <= {ADDR_LSB{1'b0}};
//for awsize = 4 bytes (010)
end
2'b10: //Wrapping burst
// The read address wraps when the address reaches wrap boundary
if (ar_wrap_en)
begin
axi_araddr <= (axi_araddr - ar_wrap_size);
end
else
begin
axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;
//araddr aligned to 4 byte boundary
axi_araddr[ADDR_LSB-1:0] <= {ADDR_LSB{1'b0}};
end
default: //reserved (incremental burst for example)
begin
axi_araddr <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB]+1;
//for arsize = 4 bytes (010)
end
endcase
end
else if((axi_arlen_cntr == axi_arlen) && ~axi_rlast && axi_arv_arr_flag )
begin
axi_rlast <= 1'b1;
end
else if (S_AXI_RREADY)
begin
axi_rlast <= 1'b0;
end
end
end

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3:axi-full-slave的axi_wready

当满足条件( ~axi_wready && S_AXI_WVALID && axi_awv_awr_flag)==1 设置axi_wready为1.这里可以看出，S_AXI_WVALID必须在一次burst中持续有效，直到满足条件(S_AXI_WLAST && axi_wready)，否则AXI-FULL-SLAVE会出错，这一点有别于AXI-LITE-SLAVE每次只读写一个数据。

// axi_wready is asserted for one S_AXI_ACLK clock cycle when both
// S_AXI_AWVALID and S_AXI_WVALID are asserted. axi_wready is
// de-asserted when reset is low.
always @( posedge S_AXI_ACLK )
begin
if ( S_AXI_ARESETN == 1'b0 )
begin
axi_wready <= 1'b0;
end
else
begin
if ( ~axi_wready && S_AXI_WVALID && axi_awv_awr_flag)
begin
// slave can accept the write data
axi_wready <= 1'b1;
end
//else if (~axi_awv_awr_flag)
else if (S_AXI_WLAST && axi_wready)
begin
axi_wready <= 1'b0;
end
end
end

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4:axi-full-slave的axi_bvalid信号

axi_bvalid用于告知axi master axi-slave端已经完成数据接收了

给出ACK，写操作LAST信号的下一个时钟，AXI-SLAVE给出ACK信号

always @( posedge S_AXI_ACLK )
begin
if ( S_AXI_ARESETN == 1'b0 )
begin
axi_bvalid <= 0;
axi_bresp <= 2'b0;
axi_buser <= 0;
end
else
begin
if (axi_awv_awr_flag && axi_wready && S_AXI_WVALID && ~axi_bvalid && S_AXI_WLAST )
begin
axi_bvalid <= 1'b1;
axi_bresp <= 2'b0;
// 'OKAY' response
end
else
begin
if (S_AXI_BREADY && axi_bvalid)
//check if bready is asserted while bvalid is high)
//(there is a possibility that bready is always asserted high)
begin
axi_bvalid <= 1'b0;
end
end
end
end

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5:axi-full-slave的axi_arready信号

当满足条件(~axi_arready && S_AXI_ARVALID && ~axi_awv_awr_flag && ~axi_arv_arr_flag)=1的时候表示可以进行一次AXI-FULL的burst读操作了，这个时候AXI -FULL-SLAVE设置axi_arready <= 1'b1和axi_arv_arr_flag <= 1'b1

// S_AXI_ARVALID is asserted. axi_awready is
// de-asserted when reset (active low) is asserted.
// The read address is also latched when S_AXI_ARVALID is
// asserted. axi_araddr is reset to zero on reset assertion.
always @( posedge S_AXI_ACLK )
begin
if ( S_AXI_ARESETN == 1'b0 )
begin
axi_arready <= 1'b0;
axi_arv_arr_flag <= 1'b0;
end
else
begin
if (~axi_arready && S_AXI_ARVALID && ~axi_awv_awr_flag && ~axi_arv_arr_flag)
begin
axi_arready <= 1'b1;
axi_arv_arr_flag <= 1'b1;
end
else if (axi_rvalid && S_AXI_RREADY && axi_arlen_cntr == axi_arlen)
// preparing to accept next address after current read completion
begin
axi_arv_arr_flag <= 1'b0;
end
else
begin
axi_arready <= 1'b0;
end
end
end

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6:axi-full-slave的axi_araddr信号

AXI-的读写操作几乎是相对的代码，AXI的burst模式包括3种：

1:fixed burst这种模式下地址都是相同的

2: incremental burst这种模式下地址递增

3: Wrapping burst 这只模式下地址达到设置的最大地址边界后返回原来的地址。

本文demo种以下三种模式的具体代码如下：

//This process is used to latch the address when both
//S_AXI_ARVALID and S_AXI_RVALID are valid.
always @( posedge S_AXI_ACLK )
begin
if ( S_AXI_ARESETN == 1'b0 )
begin
axi_araddr <= 0;
axi_arlen_cntr <= 0;
axi_arburst <= 0;
axi_arlen <= 0;
axi_rlast <= 1'b0;
axi_ruser <= 0;
end
else
begin
if (~axi_arready && S_AXI_ARVALID && ~axi_arv_arr_flag)
begin
// address latching
axi_araddr <= S_AXI_ARADDR[C_S_AXI_ADDR_WIDTH - 1:0];
axi_arburst <= S_AXI_ARBURST;
axi_arlen <= S_AXI_ARLEN;
// start address of transfer
axi_arlen_cntr <= 0;
axi_rlast <= 1'b0;
end
else if((axi_arlen_cntr <= axi_arlen) && axi_rvalid && S_AXI_RREADY)
begin
axi_arlen_cntr <= axi_arlen_cntr + 1;
axi_rlast <= 1'b0;
case (axi_arburst)
2'b00: // fixed burst
// The read address for all the beats in the transaction are fixed
begin
axi_araddr <= axi_araddr;
//for arsize = 4 bytes (010)
end
2'b01: //incremental burst
// The read address for all the beats in the transaction are increments by awsize
begin
axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;
//araddr aligned to 4 byte boundary
axi_araddr[ADDR_LSB-1:0] <= {ADDR_LSB{1'b0}};
//for awsize = 4 bytes (010)
end
2'b10: //Wrapping burst
// The read address wraps when the address reaches wrap boundary
if (ar_wrap_en)
begin
axi_araddr <= (axi_araddr - ar_wrap_size);
end
else
begin
axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB] + 1;
//araddr aligned to 4 byte boundary
axi_araddr[ADDR_LSB-1:0] <= {ADDR_LSB{1'b0}};
end
default: //reserved (incremental burst for example)
begin
axi_araddr <= axi_araddr[C_S_AXI_ADDR_WIDTH - 1:ADDR_LSB]+1;
//for arsize = 4 bytes (010)
end
endcase
end
else if((axi_arlen_cntr == axi_arlen) && ~axi_rlast && axi_arv_arr_flag )
begin
axi_rlast <= 1'b1;
end
else if (S_AXI_RREADY)
begin
axi_rlast <= 1'b0;
end
end
end

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7:axi-full-slave的axi_rvalid信号

在用VIVADO模板产生的demo中，读操作数据不是连续读的，通过axi_rvalid设置AXI-SLAVE FULL读数据有效。

always @( posedge S_AXI_ACLK )
begin
if ( S_AXI_ARESETN == 1'b0 )
begin
axi_rvalid <= 0;
axi_rresp <= 0;
end
else
begin
if (axi_arv_arr_flag && ~axi_rvalid)
begin
axi_rvalid <= 1'b1;
axi_rresp <= 2'b0;
// 'OKAY' response
end
else if (axi_rvalid && S_AXI_RREADY)
begin
axi_rvalid <= 1'b0;
end
end
end

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8:数据保存到bockram

以下是利用block ram完成数据的保存和回读

// implement Block RAM(s)
generate
for(i=0; i<= USER_NUM_MEM-1; i=i+1)
begin:BRAM_GEN
wire mem_rden;
wire mem_wren;
assign mem_wren = axi_wready && S_AXI_WVALID ;
assign mem_rden = axi_arv_arr_flag ; //& ~axi_rvalid
for(mem_byte_index=0; mem_byte_index<= (C_S_AXI_DATA_WIDTH/8-1); mem_byte_index=mem_byte_index+1)
begin:BYTE_BRAM_GEN
wire [8-1:0] data_in ;
wire [8-1:0] data_out;
reg [8-1:0] byte_ram [0 : 15];
integer j;
//assigning 8 bit data
assign data_in = S_AXI_WDATA[(mem_byte_index*8+7) -: 8];
assign data_out = byte_ram[mem_address];
always @( posedge S_AXI_ACLK )
begin
if (mem_wren && S_AXI_WSTRB[mem_byte_index])
begin
byte_ram[mem_address] <= data_in;
end
end
always @( posedge S_AXI_ACLK )
begin
if (mem_rden)
begin
mem_data_out[i][(mem_byte_index*8+7) -: 8] <= data_out;
end
end
end
end
endgenerate

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4实验结果
仿真结果：

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