1 激活层设计
LeNet-5网络的激活函数是双曲正切函数(TanH)，项目中tanh函数模块由完整的层UsingTheTanh构成，该层由较小的处理单元HyperBolicTangent组成
1.1 HyperBolicTangent
处理单元HyperBolicTangent，对每个输入执行Tanh操作，原理图如图所示，输入为位宽16的数，输出位宽也是16。该单元将Tanh运算分为3个乘法操作和1个加法操作：
- 首先，得到x项的增量项，即x^2
- 然后，将当前x项与下一项相乘
- 然后，将每个相应的最终x项与其系数相乘
- 最后，将每个结果项与前一项相加
1.2 UsingTheTanh
UsingTheTanh是Tanh层，由HyperBolicTangent单元组成，原理图如图所示。Tanh层的输入数据位宽为75264，即为卷积层的输出数据
2 代码实现
一起学习用Verilog在FPGA上实现CNN----(二)卷积层设计已经完成卷积层的设计，下面我们继续激活层的代码实现
2.1 HyperBolicTangent16
2.1.1 设计输入
创建HyperBolicTangent16文件，操作如图：
输入文件名：
确认创建：
双击打开，输入如下代码：
module HyperBolicTangent16 (x,reset,clk,OutputFinal,Finished);
parameter DATA_WIDTH=16;
localparam taylor_iter=4;//I chose 4 Taylor Coefficients to undergo my tanh operation
input signed [DATA_WIDTH-1:0] x;
input clk;
input reset;
output reg Finished;
output reg[DATA_WIDTH-1:0] OutputFinal;
reg [DATA_WIDTH*taylor_iter-1:0] Coefficients ; //-17/315 2/15 -1/3 1
wire [DATA_WIDTH-1:0] Xsquared; //To always generate a squared version of the input to increment the power by 2 always.
reg [DATA_WIDTH-1:0] ForXSqOrOne; //For Multiplying The power of X(1 or X^2)
reg [DATA_WIDTH-1:0] ForMultPrevious; //output of the first multiplication which is either with 1 or x(X or Output1)
wire [DATA_WIDTH-1:0] OutputOne; //the output of Mulitplying the X term with its corresponding power coeff.
wire [DATA_WIDTH-1:0] OutOfCoeffMult; //the output of Mulitplying the X term with its corresponding power coeff.
reg [DATA_WIDTH-1:0] OutputAdditionInAlways;
wire [DATA_WIDTH-1:0] OutputAddition; //the output of the Addition each cycle
floatMult16 MSquaring (x,x,Xsquared);//Generating x^2 得到x项的增量项，即x^2
floatMult16 MGeneratingXterm (ForXSqOrOne,ForMultPrevious,OutputOne); //Generating the X term [x,x^3,x^5,...] 将当前x项与下一项相乘
floatMult16 MTheCoefficientTerm (OutputOne,Coefficients[DATA_WIDTH-1:0],OutOfCoeffMult); //Multiplying the X term by its corresponding coeff. 将每个相应的最终x项与其系数相乘
floatAdd16 FADD1 (OutOfCoeffMult,OutputAdditionInAlways,OutputAddition); //Adding the new term to the previous one ex: x-1/3*(x^3) 将每个结果项与前一项相加
reg [DATA_WIDTH-1:0] AbsFloat; //To generate an absolute value of the input[For Checking the convergence]
always @ (posedge clk) begin
AbsFloat=x;//Here i hold the input then i make it positive whatever its sign to be able to compare to implement the rule |x|>pi/2 which is the convergence rule
AbsFloat[15]=0;
if(AbsFloat>16'sb0011111001001000)begin
//The Finished bit is for letting the bigger module know that the tanh is finished
if (x[15]==0)begin
OutputFinal= 16'b0011110000000000;Finished =1'b 1;//here i assign it an immediate value of Positive Floating one
end
if (x[15]==1)begin
OutputFinal= 16'b1011110000000000;Finished =1'b 1;//here i assign it an immediate value of Negative Floating one
end
end
//here i handle the case of it equals +- pi/2 so i got the exact value and handle it also immediately
else if (AbsFloat==16'sb0011111001001000)
begin
if (x[15]==0)begin
OutputFinal=16'b0011110000000000;Finished=1'b 1;
end
else begin
OutputFinal=16'b1011110000000000;Finished=1'b 1;
end
end
else begin
//First instance of the tanh
if(reset==1'b1)begin
Coefficients=64'b1010101011101000_0011000001000100_1011010101010101_0011110000000000;//the 4 coefficients of taylor expansion
ForXSqOrOne=16'b0011110000000000; //initially 1
OutputAdditionInAlways=16'b0000000000000000; //initially 0
ForMultPrevious=x;
Finished=0;
end
else begin
ForXSqOrOne=Xsquared;
ForMultPrevious=OutputOne; //get the output of the second multiplication to multiply with x
Coefficients=Coefficients>>DATA_WIDTH; //shift 32 bit to divide the out_m1 with the new number to compute the factorial
OutputAdditionInAlways=OutputAddition;
Finished=0;
end
// the end of the tanh
if(Coefficients==64'b0000000000000000_0000000000000000_0000000000000000_0000000000000000)begin
OutputFinal=OutputAddition;
Finished =1'b 1;
end
end
end
endmodule
如图所示：
2.1.2 分析与综合
将HyperBolicTangent16设置为顶层：
对设计进行分析，操作如图：
分析后的设计，Vivado自动生成原理图，如图：
对设计进行综合，操作如图：
综合完成，关闭即可：
2.1.3 功能仿真
创建TestBench，操作如图所示：
输入激励文件名：
双击打开，输入激励代码：
`timescale 1ns / 1ps
module tb_HyperBolicTangent16();
reg clk, reset;
reg [15:0]x;
wire [15:0]OutputFinal;
wire Finished;
localparam PERIOD = 100;
always
#(PERIOD/2) clk = ~clk;
initial begin
#0 //starting the tanh
clk = 1'b1;
reset = 1'b1;
// trying a random input(0.600000023842) where tanh(0.600000023842)=0.53704958
x=16'b0011100011001101;
#(PERIOD/2)
reset = 0;
#400
// waiting for 4 clock cycles then checking the output with approx.(0.53685)
if(OutputFinal==32'b00111111000010010110111101111011 && Finished==1'b1)begin
$display("Result is Right [Not in convergence region]");
end
else begin
$display("Result is Wrong");
end
//trying another input which will be in the convergence region(3) the output will be converged to 1 and reseting the function again
x=16'b0100001000000000;
reset = 1'b1;
#(PERIOD/2)
reset=1'b0;
#200
// checking if the output is 1
if(OutputFinal==32'b00111111100000000000000000000000)begin
$display("Result is Right [ convergence region]");
end
else begin
$display("Result is Wrong ");
end
$stop;
end
HyperBolicTangent16 UUT
(
.x(x),
.clk(clk),
.reset(reset),
.OutputFinal(OutputFinal),
.Finished(Finished)
);
endmodule
如图所示：
将tb_HyperBolicTangent16设置为顶层：
开始进行仿真，操作如下:
开始仿真，如图：
仿真波形，如图：
关闭仿真：
2.2 UsingTheTanh16
2.2.1 设计输入
创建UsingTheTanh16文件，如图：
双击打开，输入代码：
module UsingTheTanh16(x,clk,Output,resetExternal,FinishedTanh);
parameter DATA_WIDTH=16;
parameter nofinputs=7;// deterimining the no of inputs entering the function
input resetExternal;// controlling this layer
input signed [nofinputs*DATA_WIDTH-1:0] x;
input clk;
output reg FinishedTanh;
reg reset;// for the inner tanh
output reg [nofinputs*DATA_WIDTH-1:0]Output;
wire [DATA_WIDTH-1:0]OutputTemp;
reg [7:0]counter=0;
wire Finished;
reg [7:0]i;
// the inner tanh taking inputs in 32 bits and then increment using the i operator
HyperBolicTangent16 TanhArray (x[DATA_WIDTH*i+:DATA_WIDTH],reset,clk,OutputTemp,Finished);
always@(posedge clk)
begin
counter=counter+1;
// if the external reset =1 then make everything to 0
if(resetExternal==1) begin reset=1;i=0;FinishedTanh=0; end
//checking if the tanh is not finished so continue your operation and low down the reset to continue
else if(FinishedTanh==0) begin
if(reset==1)begin reset=0; end
// if it is finished then store the output of the tanh and increment the input forward
else if (Finished==1)begin Output[DATA_WIDTH*i+:DATA_WIDTH]=OutputTemp;reset=1;i=i+1;end
// check if all the inputs are finished then the layer is OK
if(i==nofinputs)
begin FinishedTanh=1;end
end
end
endmodule
如图所示：
2.2.2 分析与综合
将UsingTheTanh16设置为顶层：
关闭上次的分析文件：
对设计进行分析，操作如图：
分析后的设计，Vivado自动生成原理图，如图：
对设计进行综合，操作如图：
2.2.3 功能仿真
创建TestBench，操作如图所示：
双击打开，输入激励代码：
module tb_UsingTheTanh16();
reg clk, resetExternal;
reg [63:0]x;
wire [63:0]Output;
wire FinishedTanh;
localparam PERIOD = 100;
always
#(PERIOD/2) clk = ~clk;
initial begin
#0 //starting the tanh
clk = 1'b1;
resetExternal = 1'b1;
// trying a random input(0.6,3) where tanh(0.600000023842)=0.53704958, tanh(3)~=1
x=64'b00111111000110011001100110011010_01000000010000000000000000000000;
#(PERIOD/2)
resetExternal = 1'b0;
#800
// waiting for The final output which will be (0.57,1)
if(Output==64'b00111111000010010110111101111011_00111111100000000000000000000000 && FinishedTanh==1'b1)begin
$display("Result is right (for the full array of inputs)");
end
else begin
$display("Result is Wrong");
end
$stop;
end
UsingTheTanh16 UUT
(
.x(x),
.clk(clk),
.Output(Output),
.resetExternal(resetExternal),
.FinishedTanh(FinishedTanh)
);
endmodule
如图所示：
将tb_UsingTheTanh16文件设置为顶层：
开始进行仿真，操作如下:
开始仿真，如图：
仿真波形，如图：
2.3 IntegrationConv
2.3.1 设计输入
双击打开integrationConv文件，修改代码为：
module integrationConv (clk,reset,CNNinput,Conv,ConvOutput);
parameter DATA_WIDTH = 16;
parameter ImgInW = 32;
parameter ImgInH = 32;
parameter ConvOut = 28;
parameter Kernel = 5;
parameter DepthC = 6;
input clk, reset;
input [ImgInW*ImgInH*DATA_WIDTH-1:0] CNNinput;
input [Kernel*Kernel*DepthC*DATA_WIDTH-1:0] Conv;
output [ConvOut*ConvOut*DepthC*DATA_WIDTH-1:0] ConvOutput;
reg TanhReset;
wire TanhFlag;
wire [ConvOut*ConvOut*DepthC*DATA_WIDTH-1:0] Cout;
wire [ConvOut*ConvOut*DepthC*DATA_WIDTH-1:0] CoutTanH;
convLayerMulti C1
(
.clk(clk),
.reset(reset),
.image(CNNinput),
.filters(Conv),
.outputConv(ConvOutput)
);
UsingTheTanh16
#(.nofinputs(ConvOut*ConvOut*DepthC))
Tanh1(
.x(Cout),
.clk(clk),
.Output(CoutTanH),
.resetExternal(TanhReset),
.FinishedTanh(TanhFlag)
);
endmodule
如图所示：
2.3.2 分析与综合
将integrationConv设置为顶层：
关闭上次的分析文件：
对设计进行分析，操作如图：
分析后的设计，Vivado自动生成原理图，如图：
对设计进行综合，操作如图：
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希望本文对大家有帮助，上文若有不妥之处，欢迎指正
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