From 5d9b7a152615dfa7b015ccddd3b0bbde4307f3da Mon Sep 17 00:00:00 2001
From: Alban Gruin <alban.gruin@irit.fr>
Date: Wed, 2 Mar 2022 00:16:15 +0100
Subject: [PATCH] commit_stage: critical path improvements
Signed-off-by: Alban Gruin <alban.gruin@irit.fr>
---
src/commit_stage.sv | 74 +++++++++++++++------------------------------
1 file changed, 25 insertions(+), 49 deletions(-)
diff --git a/src/commit_stage.sv b/src/commit_stage.sv
index 42e65b8e..7ae9e2ab 100644
--- a/src/commit_stage.sv
+++ b/src/commit_stage.sv
@@ -92,22 +92,20 @@ module commit_stage import ariane_pkg::*; #(
always_comb begin : commit
// default assignments
commit_ack_o[0] = 1'b0;
- commit_ack_o[1] = 1'b0;
- amo_valid_commit_o = 1'b0;
+ // amo_valid_commit_o = 1'b0;
we_gpr_o[0] = 1'b0;
we_gpr_o[1] = 1'b0;
we_fpr_o = '{default: 1'b0};
- commit_lsu_o = 1'b0;
- commit_csr_o = 1'b0;
+ // commit_lsu_o = 1'b0;
+ // commit_csr_o = 1'b0;
// amos will commit on port 0
wdata_o[0] = (amo_resp_i.ack) ? amo_resp_i.result[riscv::XLEN-1:0] : commit_instr_i[0].result;
- wdata_o[1] = commit_instr_i[1].result;
- csr_op_o = ADD; // this corresponds to a CSR NOP
- csr_wdata_o = {riscv::XLEN{1'b0}};
+ // csr_op_o = ADD; // this corresponds to a CSR NOP
+ // csr_wdata_o = {riscv::XLEN{1'b0}};
fence_i_o = 1'b0;
- fence_o = 1'b0;
+ // fence_o = 1'b0;
sfence_vma_o = 1'b0;
csr_write_fflags_o = 1'b0;
flush_commit_o = 1'b0;
@@ -128,7 +126,7 @@ module commit_stage import ariane_pkg::*; #(
// check if the LSU is ready to accept another commit entry (e.g.: a non-speculative store)
if (commit_lsu_ready_i) begin
commit_ack_o[0] = 1'b1;
- commit_lsu_o = 1'b1;
+ // commit_lsu_o = 1'b1;
// stall in case the store buffer is not able to accept anymore instructions
end else begin
commit_ack_o[0] = 1'b0;
@@ -139,7 +137,7 @@ module commit_stage import ariane_pkg::*; #(
// ---------
if (commit_instr_i[0].fu inside {FPU, FPU_VEC}) begin
// write the CSR with potential exception flags from retiring floating point instruction
- csr_wdata_o = {{riscv::XLEN-5{1'b0}}, commit_instr_i[0].ex.cause[4:0]};
+ // csr_wdata_o = {{riscv::XLEN-5{1'b0}}, commit_instr_i[0].ex.cause[4:0]};
csr_write_fflags_o = 1'b1;
commit_ack_o[0] = 1'b1;
end
@@ -150,10 +148,10 @@ module commit_stage import ariane_pkg::*; #(
// throw an exception
if (commit_instr_i[0].fu == CSR) begin
// write the CSR file
- csr_op_o = commit_instr_i[0].op;
- csr_wdata_o = commit_instr_i[0].result;
+ // csr_op_o = commit_instr_i[0].op;
+ // csr_wdata_o = commit_instr_i[0].result;
if (!csr_exception_i.valid) begin
- commit_csr_o = 1'b1;
+ // commit_csr_o = 1'b1;
wdata_o[0] = csr_rdata_i;
commit_ack_o[0] = 1'b1;
end else begin
@@ -193,7 +191,7 @@ module commit_stage import ariane_pkg::*; #(
if (commit_instr_i[0].op == FENCE) begin
commit_ack_o[0] = no_st_pending_i;
// tell the controller to flush the D$
- fence_o = no_st_pending_i;
+ // fence_o = no_st_pending_i;
end
// ------------------
// AMO
@@ -203,49 +201,27 @@ module commit_stage import ariane_pkg::*; #(
commit_ack_o[0] = amo_resp_i.ack;
// flush the pipeline
flush_commit_o = amo_resp_i.ack;
- amo_valid_commit_o = 1'b1;
+ // amo_valid_commit_o = 1'b1;
we_gpr_o[0] = amo_resp_i.ack;
end
end
+ end
- if (NR_COMMIT_PORTS > 1) begin
- // -----------------
- // Commit Port 2
- // -----------------
- // check if the second instruction can be committed as well and the first wasn't a CSR instruction
- // also if we are in single step mode don't retire the second instruction
- if (commit_ack_o[0] && commit_instr_i[1].valid
- && !halt_i
- && !(commit_instr_i[0].fu inside {CSR})
- && !flush_dcache_i
- && !instr_0_is_amo
- && !single_step_i) begin
- // only if the first instruction didn't throw an exception and this instruction won't throw an exception
- // and the functional unit is of type ALU, LOAD, CTRL_FLOW, MULT, FPU or FPU_VEC
- if (!exception_o.valid && !commit_instr_i[1].ex.valid
- && (commit_instr_i[1].fu inside {ALU, LOAD, CTRL_FLOW, MULT, FPU, FPU_VEC})) begin
+ logic can_commit_instr;
+ assign can_commit_instr = commit_instr_i[0].valid && !commit_instr_i[0].ex.valid && !halt_i;
- if (is_rd_fpr(commit_instr_i[1].op))
- we_fpr_o[1] = 1'b1;
- else
- we_gpr_o[1] = 1'b1;
+ assign csr_op_o = (can_commit_instr && commit_instr_i[0].fu == CSR) ? commit_instr_i[0].op : ADD;
+ assign csr_wdata_o = (can_commit_instr &&
+ commit_instr_i[0].fu inside {FPU, FPU_VEC}) ? {{riscv::XLEN-5{1'b0}}, commit_instr_i[0].ex.cause[4:0]} :
+ (can_commit_instr && commit_instr_i[0].fu == CSR) ? commit_instr_i[0].result :
+ {riscv::XLEN{1'b0}};
- commit_ack_o[1] = 1'b1;
+ assign commit_csr_o = can_commit_instr && commit_instr_i[0].fu == CSR && !csr_exception_i.valid;
- // additionally check if we are retiring an FPU instruction because we need to make sure that we write all
- // exception flags
- if (commit_instr_i[1].fu inside {FPU, FPU_VEC}) begin
- if (csr_write_fflags_o)
- csr_wdata_o = {{riscv::XLEN-5{1'b0}}, (commit_instr_i[0].ex.cause[4:0] | commit_instr_i[1].ex.cause[4:0])};
- else
- csr_wdata_o = {{riscv::XLEN-5{1'b0}}, commit_instr_i[1].ex.cause[4:0]};
+ assign commit_lsu_o = can_commit_instr && commit_instr_i[0].fu == STORE && !instr_0_is_amo && commit_lsu_ready_i;
+ assign amo_valid_commit_o = can_commit_instr && RVA && instr_0_is_amo;
- csr_write_fflags_o = 1'b1;
- end
- end
- end
- end
- end
+ assign fence_o = can_commit_instr && commit_instr_i[0].op == FENCE;
// -----------------------------
// Exception & Interrupt Logic
--
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