rtl: add static branch predict unit

Signed-off-by: liangkangnan <liangkangnan@163.com>

rtl.flist

@@ -21,6 +21,7 @@
 ../rtl/core/rst_gen.sv
 ../rtl/core/tinyriscv_core.sv
 ../rtl/core/tracer.sv
+../rtl/core/bpu.sv
 
 ../rtl/debug/jtag_def.sv
 ../rtl/debug/jtag_tap.sv

rtl/core/bpu.sv

@@ -0,0 +1,62 @@
+ /*                                                                      
+ Copyright 2021 Blue Liang, liangkangnan@163.com
+                                                                         
+ Licensed under the Apache License, Version 2.0 (the "License");         
+ you may not use this file except in compliance with the License.        
+ You may obtain a copy of the License at                                 
+                                                                         
+     http://www.apache.org/licenses/LICENSE-2.0                          
+                                                                         
+ Unless required by applicable law or agreed to in writing, software    
+ distributed under the License is distributed on an "AS IS" BASIS,       
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and     
+ limitations under the License.                                          
+ */
+
+`include "defines.sv"
+
+// 静态分支预测模块
+module bpu(
+
+	input wire clk,
+	input wire rst_n,
+
+    input wire[31:0] inst_i,
+    input wire inst_valid_i,
+    input wire[31:0] pc_i,
+
+    output wire prdt_taken_o,
+    output wire[31:0] prdt_addr_o
+
+    );
+
+    wire[6:0] opcode = inst_i[6:0];
+
+    wire opcode_1100011 = (opcode == 7'b1100011);
+    wire opcode_1101111 = (opcode == 7'b1101111);
+
+    wire inst_type_branch = opcode_1100011;
+    wire inst_jal = opcode_1101111;
+
+    wire[31:0] inst_b_type_imm = {{20{inst_i[31]}}, inst_i[7], inst_i[30:25], inst_i[11:8], 1'b0};
+    wire[31:0] inst_j_type_imm = {{12{inst_i[31]}}, inst_i[19:12], inst_i[20], inst_i[30:21], 1'b0};
+
+    wire prdt_taken = (inst_type_branch & inst_b_type_imm[31]) | inst_jal;
+
+    reg[31:0] prdt_imm;
+
+    always @ (*) begin
+        prdt_imm = inst_b_type_imm;
+
+        case (1'b1)
+            inst_type_branch: prdt_imm = inst_b_type_imm;
+            inst_jal:         prdt_imm = inst_j_type_imm;
+            default: ;
+        endcase
+    end
+
+    assign prdt_taken_o = inst_valid_i ? prdt_taken : 1'b0;
+    assign prdt_addr_o = pc_i + prdt_imm;
+
+endmodule

rtl/core/exu.sv

@@ -77,6 +77,8 @@ module exu(
 
     );
 
+    wire[31:0] next_pc = dec_pc_i + 4'h4;
+
     // dispatch to ALU
     wire[31:0] alu_op1_o;
     wire[31:0] alu_op2_o;
@@ -106,6 +108,7 @@ module exu(
     wire bjp_op_bltu_o;
     wire bjp_op_bge_o;
     wire bjp_op_bgeu_o;
+    wire bjp_op_jalr_o;
     // dispatch to MULDIV
     wire req_muldiv_o;
     wire[31:0] muldiv_op1_o;
@@ -184,6 +187,7 @@ module exu(
         .bjp_op_bltu_o(bjp_op_bltu_o),
         .bjp_op_bge_o(bjp_op_bge_o),
         .bjp_op_bgeu_o(bjp_op_bgeu_o),
+        .bjp_op_jalr_o(bjp_op_jalr_o),
         // dispatch to MULDIV
         .req_muldiv_o(req_muldiv_o),
         .muldiv_op1_o(muldiv_op1_o),
@@ -357,7 +361,7 @@ module exu(
         .csr_reg_wdata_i(csr_rdata_i),
         .req_bjp_i(req_bjp_o),
         .bjp_reg_we_i(bjp_op_jump_o),
-        .bjp_reg_wdata_i(next_pc_i),
+        .bjp_reg_wdata_i(next_pc),
         .bjp_reg_waddr_i(rd_waddr_i),
         .rd_we_i(rd_we_i),
         .rd_waddr_i(rd_waddr_i),
@@ -369,10 +373,21 @@ module exu(
 
     assign reg_we_o = commit_reg_we_o & (~int_stall_i);
 
-    wire inst_jump = bjp_cmp_res_o | bjp_op_jump_o | sys_op_fence_o;
-    assign jump_flag_o = (inst_jump & (~int_stall_i)) | int_assert_i;
+                       // jal
+    wire prdt_taken = ((~bjp_op_jalr_o) & bjp_op_jump_o) |
+                       // bxx & imm[31]
+                      (req_bjp_o & (~bjp_op_jump_o) & dec_imm_i[31]);
+
+    // bxx分支预测错误
+    wire prdt_taken_error = prdt_taken & (~bjp_cmp_res_o) & req_bjp_o & (~bjp_op_jump_o);
+
+    wire inst_jump = (bjp_cmp_res_o & (~prdt_taken)) |
+                     (bjp_op_jump_o & (~prdt_taken)) |
+                     sys_op_fence_o;
+    assign jump_flag_o = ((inst_jump | prdt_taken_error) & (~int_stall_i)) | int_assert_i;
     assign jump_addr_o = int_assert_i? int_addr_i:
-                         sys_op_fence_o? next_pc_i:
+                         sys_op_fence_o? next_pc:
+                         prdt_taken_error? next_pc:
                          bjp_res_o;
     assign hold_flag_o = muldiv_stall_o | mem_stall_o;
 

rtl/core/exu_dispatch.sv

@@ -58,6 +58,7 @@ module exu_dispatch(
     output wire bjp_op_bltu_o,
     output wire bjp_op_bge_o,
     output wire bjp_op_bgeu_o,
+    output wire bjp_op_jalr_o,
 
     // dispatch to MULDIV
     output wire req_muldiv_o,
@@ -152,6 +153,7 @@ module exu_dispatch(
     assign bjp_op_bge_o = bjp_info[`DECINFO_BJP_BGE];
     assign bjp_op_bgeu_o = bjp_info[`DECINFO_BJP_BGEU];
     assign req_bjp_o = op_bjp;
+    assign bjp_op_jalr_o = bjp_op1_rs1;
 
     // MULDIV info
     wire op_muldiv = (disp_info_grp == `DECINFO_GRP_MULDIV);

rtl/core/ifu.sv

@@ -48,6 +48,8 @@ module ifu(
 
     reg[1:0] state;
     reg[1:0] next_state;
+    wire prdt_taken;
+    wire[31:0] prdt_addr;
 
     always @ (posedge clk or negedge rst_n) begin
         if (!rst_n) begin
@@ -90,6 +92,7 @@ module ifu(
     wire fetch_addr_en = instr_req_o & instr_gnt_i & (~stall_i[`STALL_PC]);
 
     assign fetch_addr_d = flush_i? flush_addr_i:
+                          prdt_taken? prdt_addr:
                           stall_i[`STALL_PC]? fetch_addr_q:
                           inst_valid? fetch_addr_q + 4'h4:
                           fetch_addr_q;
@@ -106,4 +109,14 @@ module ifu(
     assign instr_addr_o = {fetch_addr_d[31:2], 2'b00};
     assign pc_o = fetch_addr_q;
 
+    bpu u_bpu(
+        .clk(clk),
+        .rst_n(rst_n),
+        .inst_i(instr_rdata_i),
+        .inst_valid_i(inst_valid),
+        .pc_i(fetch_addr_q),
+        .prdt_taken_o(prdt_taken),
+        .prdt_addr_o(prdt_addr)
+    );
+
 endmodule