超前进位加法器代码分析
为什么 cin首先从这里输入，cla c2(ggp,ggg,cin,ggc,gggp,gggg);而且低层的进位都有高层来产生吗？
//超前进位加法器
`define word_size 32
`define word [`word_size-1:0]
`define n 4
`define slice [`n-1:0]
`define s0 (1*`n)-1:0*`n
`define s1 (2*`n)-1:1*`n
`define s2 (3*`n)-1:2*`n
`define s3 (4*`n)-1:3*`n
`define s4 (5*`n)-1:4*`n
`define s5 (6*`n)-1:5*`n
`define s6 (7*`n)-1:6*`n
`define s7 (8*`n)-1:7*`n
module c_adder (a,b,cin,s,cout);//顶层模块
input`word a,b;
input cin;
output`word s;
output cout;
wire gg,gp,gc; //
wire ggg,ggp,ggc;//
wire gggg,gggp; //
//first level
bitslice i0(a[`s0],b[`s0],gc,s[`s0],gp,gg);
bitslice i1(a[`s1],b[`s1],gc,s[`s1],gp,gg);
bitslice i2(a[`s2],b[`s2],gc,s[`s2],gp,gg);
bitslice i3(a[`s3],b[`s3],gc,s[`s3],gp,gg);
bitslice i4(a[`s4],b[`s4],gc,s[`s4],gp,gg);
bitslice i5(a[`s5],b[`s5],gc,s[`s5],gp,gg);
bitslice i6(a[`s6],b[`s6],gc,s[`s6],gp,gg);
bitslice i7(a[`s7],b[`s7],gc,s[`s7],gp,gg);
//second level
cla c0(gp,gg,ggc,gc,ggp,ggg);
cla c1(gp,gg,ggc,gc,ggp,ggg);
assign ggp=2'b11;
assign ggg=2'b00;
//third level
cla c2(ggp,ggg,cin,ggc,gggp,gggg);
assign cout=gggg|(gggp&cin);
endmodule
//求和并按输出a,b,cin分组
module bitslice(a,b,cin,s,gp,gg);
input`slice a,b;
input cin;
output`slice s;
output gp,gg;
wire`slice p,g,c;
pg i1(a,b,p,g);
cla i2(p,g,cin,c,gp,gg);
sum i3(a,b,c,s);
endmodule
//计算传播值和产生值的PG模块
module pg(a,b,p,g);
input`slice a,b;
output `slice p,g;
assignp=a|b;
assigng=a&b;
endmodule
//计算sum值的sum模块
module sum(a,b,c,s);
input`slice a,b,c;
output`slice s;
wire`slice t=a^b;
assign s=t^c;
endmodule
//n-bit 超前进位模块
module cla (p,g,cin,c,gp,gg);
input`slice p,g; //输出的propagate bit 和generate bit
input cin; //进位输入
output`slice c; //为每一位产生进位
output gp,gg; //传播值和进位制
function do_cla; //该函数内将为每个位计算其进位值
input `slice p,g;
input cin;
begin: label
integer i;
reg gp,gg;
reg`slice c;
gp=p;
gg=g;
c=cin;
for (i=1;i<`n;i=i+1)
begin
//C0=G0+P0C_1
//C1=G1+P1C0=(G1+P1G0)+P1P0C_1
gp=gp&p;
gg=(gg&p)|g;
c=(c&p)|g;
end
do_cla={c,gp,gg};
end
endfunction
assign {c,gp,gg}=do_cla(p,g,cin);
endmodule 超前进位加法器代码分析
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