cordic算法原理及verilog实现
算法原理
由此我们可以推出,当(x0,y0)与(x1,y1)的夹角为Θ时,满足如下关系:
由此可得,当(x1,y1)长度为1时,,当根据坐标旋转法旋转Θ角度后,坐标点变为(1,0)。因此,根据cordic算法求就是将初始线段旋转至(1,0)后,所得的(x,y)的值。
下面,我们将这些旋转步骤细化,看看每一步是如何工作的。
假设第n次旋转为顺时针旋转时,会得到如下结果:
此时提取会得到如下公式:
令每次旋转的角度Θ满足,则每次旋转最终的角度Θ满足:,且当顺时针旋转时,逆时针旋转时。结合以上公式我们可以得到: 因此每次迭代都能提出来,最后他们的乘积是个常数K:
因此我们的计算过程是从点(1,0)开始,每次旋转角度,Xn与Yn每次只需做移位运算即可。最终当等于Θ时,所得到的即为。
基于FPGA的算法设计
采用十六位补码的形式来表示输入角度和输出结果。输入角度采用角度制。十六位补码形式为:第一位表示符号位,第二位到第九位共八位表示整数位,第十位到第十六位共七位表示小数位。
采用十六级流水线的形式实现算法。每级流水线实现一次迭代。迭代开始之前需要先计算满足的Θ的值,并将他们转换成角度的表示形式存储起来作为中间变量。
在开始迭代之前,还要先将输入的角度转换为第一象限0-90度之间的角度进行迭代计算,并用一个flag位标识角度的正负。若为输入角度为负,则flag值为1,若角度为正,则flag值为0。此外还有九组临时变量x、y、z分别用来存储对应的横坐标、纵坐标以及剩余角度。
开始迭代之后,每次迭代都要根据cordic算法推出的公式计算x、y、z的值并将它们存储在中间变量中。
迭代完成之后,根据flag以及x8、y8的值计算最终的结果。如果flag值为1说明输入角度为负数,则将sinΘ等于(~y8+1),否则sinΘ等于y8。无论flag值为多少,cosΘ均等与x8。
verilog代码实现
module cordic_2(rst,clk,datain,sin,cos);
input rst,clk;
input[15:0] datain;
output[15:0]sin,cos;
reg[15:0]sin,cos;
parameter[15:0] rot1 = 16'b0000110101001000,
rot2 = 16'b0000011100101110,
rot3 = 16'b0000001110010000,
rot4 = 16'b0000000111001010,
rot5 = 16'b0000000011100101,
rot6 = 16'b0000000001110011,
rot7 = 16'b0000000000111001,
rot0 = 16'b0001011010000000;//parameter[15:0] k = 16'b0000000001001110;parameter[15:0] k = 16'h004d;
reg[15:0] x0,y0,z0;
reg[15:0] x1,y1,z1;
reg[15:0] x2,y2,z2;
reg[15:0] x3,y3,z3;
reg[15:0] x4,y4,z4;
reg[15:0] x5,y5,z5;
reg[15:0] x6,y6,z6;
reg[15:0] x7,y7,z7;
reg[15:0] x8,y8,z8;
reg flag0,flag1,flag2,flag3,flag4,flag5,flag6,flag7,flag8;//initialalways @(posedge clk or negedge rst)begin
if(!rst) begin
x0 <= 0;
y0 <= 0;
z0 <= 0;
flag0 <= 0; end
else if(datain == 0) begin
x0 <= 0;
y0 <= 0;
z0 <= 0;
flag0 <= 0; end
else
begin
x0 <= k;
y0 <= 0; if(datain[15])
z0 <= ~(datain-1); else
z0 <= datain;
flag0 <= datain[15]; endend//1always @(posedge clk or negedge rst)begin
if(!rst) begin
x1 <= 0;
y1 <= 0;
z1 <= 0;
flag1 <= 0; end
else
begin// if(z0[15])// begin// x1 <= x0 + y0;// y1 <= x0 - y0;// z1 <= z0 + rot0;// flag1 <= flag0;// end// else// begin
x1 <= x0 - y0;
y1 <= x0 + y0;
z1 <= z0 - rot0;
flag1 <= flag0;// end
endend//2always @(posedge clk or negedge rst)begin
if(!rst) begin
x2 <= 0;
y2 <= 0;
z2 <= 0;
flag2 <= 0; end
else
begin
if(z1[15]) begin
x2 <= x1 + {y1[15],y1[15:1]};
y2 <= y1 - {x1[15],x1[15:1]};
z2 <= z1 + rot1;
flag2 <= flag1; end
else
begin
x2 <= x1 - {y1[15],y1[15:1]};
y2 <= y1 + {x1[15],x1[15:1]};
z2 <= z1 - rot1;
flag2 <= flag1; end
endend//3always @(posedge clk or negedge rst)begin
if(!rst) begin
x3 <= 0;
y3 <= 0;
z3 <= 0;
flag3 <= 0; end
else
begin
if(z2[15]) begin
x3 <= x2 + {{2{y2[15]}},y2[15:2]};
y3 <= y2 - {{2{x2[15]}},x2[15:2]};
z3 <= z2 + rot2;
flag3 <= flag2; end
else
begin
x3 <= x2 - {{2{y2[15]}},y2[15:2]};
y3 <= y2 + {{2{x2[15]}},x2[15:2]};
z3 <= z2 - rot2;
flag3 <= flag2; end
endend//4always @(posedge clk or negedge rst)begin
if(!rst) begin
x4 <= 0;
y4 <= 0;
z4 <= 0;
flag4 <= 0; end
else
begin
if(z3[15]) begin
x4 <= x3 + {{3{y3[15]}},y3[15:3]};
y4 <= y3 - {{3{x3[15]}},x3[15:3]};
z4 <= z3 + rot3;
flag4 <= flag3; end
else
begin
x4 <= x3 - {{3{y3[15]}},y3[15:3]};
y4 <= y3 + {{3{x3[15]}},x3[15:3]};
z4 <= z3 - rot3;
flag4 <= flag3; end
endend//5always @(posedge clk or negedge rst)begin
if(!rst) begin
x5 <= 0;
y5 <= 0;
z5 <= 0;
flag5 <= 0; end
else
begin
if(z4[15]) begin
x5 <= x4 + {{4{y4[15]}},y4[15:4]};
y5 <= y4 - {{4{x4[15]}},x4[15:4]};
z5 <= z4 + rot4;
flag5 <= flag4; end
else
begin
x5 <= x4 - {{4{y4[15]}},y4[15:4]};
y5 <= y4 + {{4{x4[15]}},x4[15:4]};
z5 <= z4 - rot4;
flag5 <= flag4; end
endend//6always @(posedge clk or negedge rst)begin
if(!rst) begin
x6 <= 0;
y6 <= 0;
z6 <= 0;
flag6 <= 0; end
else
begin
if(z5[15]) begin
x6 <= x5 + {{5{y5[15]}},y5[15:5]};
y6 <= y5 - {{5{x5[15]}},x5[15:5]};
z6 <= z5 + rot5;
flag6 <= flag5; end
else
begin
x6 <= x5 - {{5{y5[15]}},y5[15:5]};
y6 <= y5 + {{5{x5[15]}},x5[15:5]};
z6 <= z5 - rot5;
flag6 <= flag5; end
endend//7always @(posedge clk or negedge rst)begin
if(!rst) begin
x7 <= 0;
y7 <= 0;
z7 <= 0;
flag7 <= 0; end
else
begin
if(z6[15]) begin
x7 <= x6 + {{6{y6[15]}},y6[15:6]};
y7 <= y6 - {{6{x6[15]}},x6[15:6]};
z7 <= z6 + rot6;
flag7 <= flag6; end
else
begin
x7 <= x6 - {{6{y6[15]}},y6[15:6]};
y7 <= y6 + {{6{x6[15]}},x6[15:6]};
z7 <= z6 - rot6;
flag7 <= flag6; end
endend//8always @(posedge clk or negedge rst)begin
if(!rst) begin
x8 <= 0;
y8 <= 0;
z8 <= 0;
flag8 <= 0; end
else
begin
if(z7[15]) begin
x8 <= x7 + {{7{y7[15]}},y7[15:7]};
y8 <= y7 - {{7{x7[15]}},x7[15:7]};
z8 <= z7 + rot7;
flag8 <= flag7; end
else
begin
x8 <= x7 - {{7{y7[15]}},y7[15:7]};
y8 <= y7 + {{7{x7[15]}},x7[15:7]};
z8 <= z7 - rot7;
flag8 <= flag7; end
endendalways @(posedge clk or negedge rst)begin
if(!rst) begin
sin <= 0;
cos <= 0; end
else
begin
if(flag8) begin
sin <= (~y8)+1;
cos <= x8; end
else
begin
sin <= y8;
cos <= x8; end
endendendmodule
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4.结果
输入值:
sin值:
cos值: