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globalbranchpredictor.v
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globalbranchpredictor.v
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module globalbranchpredictor(clk,pcsrcd,pcsrcd2,pcd,pcbranchd,pcbranchd2,originalpc,pcnext,clrbp);
input clk;
input [1:0] pcsrcd,pcsrcd2;
input [63:0] originalpc;
input [31:0] pcbranchd,pcbranchd2, pcd;
output reg [31:0] pcnext;
output reg clrbp;
reg [71:0] branchtargetbuffer[127:0];
reg [31:0] pcstorage;
reg [1:0] global;
//66 bits, first 32 bits address, next 32 bits predicted address, 2 bits T/NT
integer i;
reg foundflag, pcdfoundflag; // foundflag for Prediction, pcdfoundflag for mispredictions
initial begin
global = 2'b00;
for (i=0; i<128; i=i+1) begin
branchtargetbuffer[i] = 72'bx;
end
end
integer j=0;
integer count=0;
integer recorder;
always @(negedge clk) begin
// IF Stage
foundflag = 1'b0;
pcdfoundflag = 1'b0;
for (i=0; i<128; i=i+1) begin
if (pcd==branchtargetbuffer[i][71:40]) begin
pcdfoundflag = 1'b1;
recorder = i;
end
if (originalpc[63:32]==branchtargetbuffer[i][71:40] ) begin
case(global)
2'b00: begin
if (!branchtargetbuffer[i][7]) begin
pcstorage = originalpc[63:32];
pcnext = branchtargetbuffer[i][39:8];
end
end
2'b01: begin
if (!branchtargetbuffer[i][5]) begin
pcstorage = originalpc[63:32];
pcnext = branchtargetbuffer[i][39:8];
end
end
2'b10: begin
if (!branchtargetbuffer[i][3]) begin
pcstorage = originalpc[63:32];
pcnext = branchtargetbuffer[i][39:8];
end
end
2'b11: begin
if (!branchtargetbuffer[i][1]) begin
pcstorage = originalpc[63:32];
pcnext = branchtargetbuffer[i][39:8];
end
end
endcase
foundflag = 1'b1;
recorder = i;
end
else if (originalpc[31:0]==branchtargetbuffer[i][71:40] ) begin
case(global)
2'b00: begin
if (!branchtargetbuffer[i][7]) begin
pcstorage = originalpc[31:0];
pcnext = branchtargetbuffer[i][39:8];
end
end
2'b01: begin
if (!branchtargetbuffer[i][5]) begin
pcstorage = originalpc[31:0];
pcnext = branchtargetbuffer[i][39:8];
end
end
2'b10: begin
if (!branchtargetbuffer[i][3]) begin
pcstorage = originalpc[31:0];
pcnext = branchtargetbuffer[i][39:8];
end
end
2'b11: begin
if (!branchtargetbuffer[i][1]) begin
pcstorage = originalpc[31:0];
pcnext = branchtargetbuffer[i][39:8];
end
end
endcase
foundflag = 1'b1;
recorder = i;
end
end
// ID and EX Stages
// found? - Yes
if (foundflag) begin
clrbp = 1'b0;
// Update the existing buffer to a higher taken
case(global)
2'b00: begin
global = 2'b00;
case(branchtargetbuffer[recorder][7:6])
2'b00: branchtargetbuffer[recorder][7:6] = 2'b00;
2'b01: branchtargetbuffer[recorder][7:6] = 2'b00;
2'b10: branchtargetbuffer[recorder][7:6] = 2'b01;
2'b11: branchtargetbuffer[recorder][7:6] = 2'b10;
endcase
end
2'b01: begin
global = 2'b00;
case(branchtargetbuffer[recorder][5:4])
2'b00: branchtargetbuffer[recorder][5:4] = 2'b00;
2'b01: branchtargetbuffer[recorder][5:4] = 2'b00;
2'b10: branchtargetbuffer[recorder][5:4] = 2'b01;
2'b11: branchtargetbuffer[recorder][5:4] = 2'b10;
endcase
end
2'b10: begin
global = 2'b01;
case(branchtargetbuffer[recorder][3:2])
2'b00: branchtargetbuffer[recorder][3:2] = 2'b00;
2'b01: branchtargetbuffer[recorder][3:2] = 2'b00;
2'b10: branchtargetbuffer[recorder][3:2] = 2'b01;
2'b11: branchtargetbuffer[recorder][3:2] = 2'b10;
endcase
end
2'b11: begin
global = 2'b10;
case(branchtargetbuffer[recorder][1:0])
2'b00: branchtargetbuffer[recorder][1:0] = 2'b00;
2'b01: branchtargetbuffer[recorder][1:0] = 2'b00;
2'b10: branchtargetbuffer[recorder][1:0] = 2'b01;
2'b11: branchtargetbuffer[recorder][1:0] = 2'b10;
endcase
end
endcase
end
// Misprediction
else if (!pcsrcd[0] && pcdfoundflag) begin
// Put back old count and issue a clr signal to pipefd
clrbp = 1'b1;
pcnext = pcstorage;
// Update the existing buffer to a lower taken
case(global)
2'b00: begin
global = 2'b01;
case(branchtargetbuffer[recorder][7:6])
2'b00: branchtargetbuffer[recorder][7:6] = 2'b01;
2'b01: branchtargetbuffer[recorder][7:6] = 2'b10;
2'b10: branchtargetbuffer[recorder][7:6] = 2'b11;
2'b11: branchtargetbuffer[recorder][7:6] = 2'b11;
endcase
end
2'b01: begin
global = 2'b11;
case(branchtargetbuffer[recorder][5:4])
2'b00: branchtargetbuffer[recorder][5:4] = 2'b01;
2'b01: branchtargetbuffer[recorder][5:4] = 2'b10;
2'b10: branchtargetbuffer[recorder][5:4] = 2'b11;
2'b11: branchtargetbuffer[recorder][5:4] = 2'b11;
endcase
end
2'b10: begin
global = 2'b01;
case(branchtargetbuffer[recorder][3:2])
2'b00: branchtargetbuffer[recorder][3:2] = 2'b01;
2'b01: branchtargetbuffer[recorder][3:2] = 2'b10;
2'b10: branchtargetbuffer[recorder][3:2] = 2'b11;
2'b11: branchtargetbuffer[recorder][3:2] = 2'b11;
endcase
end
2'b11: begin
global = 2'b11;
case(branchtargetbuffer[recorder][1:0])
2'b00: branchtargetbuffer[recorder][1:0] = 2'b01;
2'b01: branchtargetbuffer[recorder][1:0] = 2'b10;
2'b10: branchtargetbuffer[recorder][1:0] = 2'b11;
2'b11: branchtargetbuffer[recorder][1:0] = 2'b11;
endcase
end
endcase
end
//found? - No
else begin
if (pcsrcd[0]) begin//branch taken
// Write into buffer at next available spot
branchtargetbuffer[count][7:0] = 8'b0;
branchtargetbuffer[count][39:8] = pcbranchd;
branchtargetbuffer[count][71:40] = pcd;
pcnext = pcbranchd;
clrbp = 1'b0;
count = count + 1;
if (count > 127)
count = 0;
case(global)
2'b00: global=2'b00;
2'b01: global=2'b10;
2'b10: global=2'b00;
2'b11: global=2'b10;
endcase
end
else if (pcsrcd2[0]) begin//branch taken
// Write into buffer at next available spot
branchtargetbuffer[count][7:0] = 8'b0;
branchtargetbuffer[count][39:8] = pcbranchd2;
branchtargetbuffer[count][71:40] = pcd;
pcnext = pcbranchd2;
clrbp = 1'b0;
count = count + 1;
if (count > 127)
count = 0;
case(global)
2'b00: global=2'b00;
2'b01: global=2'b10;
2'b10: global=2'b00;
2'b11: global=2'b10;
endcase
end
else begin//branch not taken
clrbp = 1'b0;
pcnext = originalpc[63:32];
case(global)
2'b00: global=2'b01;
2'b01: global=2'b11;
2'b10: global=2'b01;
2'b11: global=2'b11;
endcase
end
end
end
endmodule