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Add New Stall and Flush Signals to acc_dispatcher (#1317)
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* [lsu] Add external store buffer pending stall signal

* [controller] Add external acc request pipeline flush signal

* [frontend] Do not increment commit pc on flush if commit stage is halted

* [acc_dispatcher] Add new store buffer stall and flush pipeline ctrl signals

* [acc_dispatcher] Add top module passable config type and parameter

* [cva6] Pass on missing CVA6Cfg parameter to acc_dispatcher
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@domenicw
domenicw authored Jul 26, 2023
1 parent 716d21c commit 1a13d6c
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Showing 8 changed files with 46 additions and 8 deletions.
14 changes: 13 additions & 1 deletion core/acc_dispatcher.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,9 @@
module acc_dispatcher import ariane_pkg::*; import riscv::*; #(
parameter ariane_pkg::cva6_cfg_t CVA6Cfg = ariane_pkg::cva6_cfg_empty,
parameter type acc_req_t = acc_pkg::accelerator_req_t,
parameter type acc_resp_t = acc_pkg::accelerator_resp_t
parameter type acc_resp_t = acc_pkg::accelerator_resp_t,
parameter type acc_cfg_t = logic,
parameter acc_cfg_t AccCfg = '0
) (
input logic clk_i,
input logic rst_ni,
Expand All @@ -43,11 +45,14 @@ module acc_dispatcher import ariane_pkg::*; import riscv::*; #(
input logic [CVA6Cfg.NrCommitPorts-1:0] commit_ack_i,
input logic commit_st_barrier_i, // A store barrier was commited
// Interface with the load/store unit
output logic acc_stall_st_pending_o,
input logic acc_no_st_pending_i,
input dcache_req_i_t [2:0] dcache_req_ports_i,
// Interface with the controller
output logic ctrl_halt_o,
input logic flush_unissued_instr_i,
input logic flush_ex_i,
output logic flush_pipeline_o,
// Interface with cache subsystem
input logic inval_ready_i,
output logic inval_valid_o,
Expand Down Expand Up @@ -401,4 +406,11 @@ module acc_dispatcher import ariane_pkg::*; import riscv::*; #(
@(posedge clk_i) disable iff (~rst_ni) (acc_spec_stores_overflow == 1'b0) && (acc_disp_stores_overflow == 1'b0) )
else $error("[acc_dispatcher] Too many pending stores.");

/**************************
* Tie Off Unused Signals *
**************************/

assign acc_stall_st_pending_o = 1'b0;
assign flush_pipeline_o = 1'b0;

endmodule : acc_dispatcher
7 changes: 4 additions & 3 deletions core/controller.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,8 @@ module controller import ariane_pkg::*; #(
input logic fence_i_i, // fence.i in
input logic fence_i, // fence in
input logic sfence_vma_i, // We got an instruction to flush the TLBs and pipeline
input logic flush_commit_i // Flush request from commit stage
input logic flush_commit_i, // Flush request from commit stage
input logic flush_acc_i // Flush request from accelerator
);

// active fence - high if we are currently flushing the dcache
Expand Down Expand Up @@ -132,8 +133,8 @@ module controller import ariane_pkg::*; #(
flush_tlb_o = 1'b1;
end

// Set PC to commit stage and flush pipleine
if (flush_csr_i || flush_commit_i) begin
// Set PC to commit stage and flush pipeline
if (flush_csr_i || flush_commit_i || flush_acc_i) begin
set_pc_commit_o = 1'b1;
flush_if_o = 1'b1;
flush_unissued_instr_o = 1'b1;
Expand Down
15 changes: 15 additions & 0 deletions core/cva6.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -114,6 +114,8 @@ module cva6 import ariane_pkg::*; #(
},
//
parameter ariane_pkg::ariane_cfg_t ArianeCfg = ariane_pkg::ArianeDefaultConfig,
parameter type acc_cfg_t = logic,
parameter acc_cfg_t AccCfg = '0,
parameter type cvxif_req_t = cvxif_pkg::cvxif_req_t,
parameter type cvxif_resp_t = cvxif_pkg::cvxif_resp_t
) (
Expand Down Expand Up @@ -252,6 +254,7 @@ module cva6 import ariane_pkg::*; #(
logic lsu_commit_commit_ex;
logic lsu_commit_ready_ex_commit;
logic [TRANS_ID_BITS-1:0] lsu_commit_trans_id;
logic stall_st_pending_ex;
logic no_st_pending_ex;
logic no_st_pending_commit;
logic amo_valid_commit;
Expand Down Expand Up @@ -335,6 +338,7 @@ module cva6 import ariane_pkg::*; #(
logic dcache_flush_ack_cache_ctrl;
logic set_debug_pc;
logic flush_commit;
logic flush_acc;

icache_areq_i_t icache_areq_ex_cache;
icache_areq_o_t icache_areq_cache_ex;
Expand Down Expand Up @@ -373,6 +377,7 @@ module cva6 import ariane_pkg::*; #(
) i_frontend (
.flush_i ( flush_ctrl_if ), // not entirely correct
.flush_bp_i ( 1'b0 ),
.halt_i ( halt_ctrl ),
.debug_mode_i ( debug_mode ),
.boot_addr_i ( boot_addr_i[riscv::VLEN-1:0] ),
.icache_dreq_i ( icache_dreq_cache_if ),
Expand Down Expand Up @@ -578,6 +583,7 @@ module cva6 import ariane_pkg::*; #(
.lsu_commit_i ( lsu_commit_commit_ex ), // from commit
.lsu_commit_ready_o ( lsu_commit_ready_ex_commit ), // to commit
.commit_tran_id_i ( lsu_commit_trans_id ), // from commit
.stall_st_pending_i ( stall_st_pending_ex ),
.no_st_pending_o ( no_st_pending_ex ),
// FPU
.fpu_ready_o ( fpu_ready_ex_id ),
Expand Down Expand Up @@ -816,6 +822,7 @@ module cva6 import ariane_pkg::*; #(
.fence_i ( fence_commit_controller ),
.sfence_vma_i ( sfence_vma_commit_controller ),
.flush_commit_i ( flush_commit ),
.flush_acc_i ( flush_acc ),

.flush_icache_o ( icache_flush_ctrl_cache ),
.*
Expand Down Expand Up @@ -920,13 +927,17 @@ module cva6 import ariane_pkg::*; #(

if (ENABLE_ACCELERATOR) begin: gen_accelerator
acc_dispatcher #(
.CVA6Cfg ( CVA6Cfg ),
.acc_cfg_t ( acc_cfg_t ),
.AccCfg ( AccCfg ),
.acc_req_t ( cvxif_req_t ),
.acc_resp_t ( cvxif_resp_t )
) i_acc_dispatcher (
.clk_i ( clk_i ),
.rst_ni ( rst_ni ),
.flush_unissued_instr_i ( flush_unissued_instr_ctrl_id ),
.flush_ex_i ( flush_ctrl_ex ),
.flush_pipeline_o ( flush_acc ),
.acc_cons_en_i ( acc_cons_en_csr ),
.acc_fflags_valid_o ( acc_resp_fflags_valid ),
.acc_fflags_o ( acc_resp_fflags ),
Expand All @@ -944,7 +955,9 @@ module cva6 import ariane_pkg::*; #(
.acc_exception_o ( acc_exception_ex_id ),
.acc_valid_ex_o ( acc_valid_acc_ex ),
.commit_ack_i ( commit_ack ),
.acc_stall_st_pending_o ( stall_st_pending_ex ),
.acc_no_st_pending_i ( no_st_pending_commit ),
.dcache_req_ports_i ( dcache_req_ports_ex_cache ),
.ctrl_halt_o ( halt_acc_ctrl ),
.inval_ready_i ( inval_ready ),
.inval_valid_o ( inval_valid ),
Expand All @@ -963,6 +976,8 @@ module cva6 import ariane_pkg::*; #(
assign dirty_v_state = '0;
assign acc_valid_acc_ex = '0;
assign halt_acc_ctrl = '0;
assign stall_st_pending_ex = '0;
assign flush_acc = '0;

// No invalidation interface
assign inval_valid = '0;
Expand Down
2 changes: 2 additions & 0 deletions core/ex_stage.sv
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Expand Up @@ -66,6 +66,7 @@ module ex_stage import ariane_pkg::*; #(
input logic lsu_commit_i,
output logic lsu_commit_ready_o, // commit queue is ready to accept another commit request
input logic [TRANS_ID_BITS-1:0] commit_tran_id_i,
input logic stall_st_pending_i,
output logic no_st_pending_o,
input logic amo_valid_commit_i,
// FPU
Expand Down Expand Up @@ -307,6 +308,7 @@ module ex_stage import ariane_pkg::*; #(
.clk_i,
.rst_ni,
.flush_i,
.stall_st_pending_i,
.no_st_pending_o,
.fu_data_i ( lsu_data ),
.lsu_ready_o,
Expand Down
9 changes: 6 additions & 3 deletions core/frontend/frontend.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ module frontend import ariane_pkg::*; #(
input logic rst_ni, // Asynchronous reset active low
input logic flush_i, // flush request for PCGEN
input logic flush_bp_i, // flush branch prediction
input logic halt_i, // halt commit stage
input logic debug_mode_i,
// global input
input logic [riscv::VLEN-1:0] boot_addr_i,
Expand Down Expand Up @@ -338,12 +339,14 @@ module frontend import ariane_pkg::*; #(
// 6. Pipeline Flush because of CSR side effects
// On a pipeline flush start fetching from the next address
// of the instruction in the commit stage
// we came here from a flush request of a CSR instruction or AMO,
// as CSR or AMO instructions do not exist in a compressed form
// we either came here from a flush request of a CSR instruction or AMO,
// so as CSR or AMO instructions do not exist in a compressed form
// we can unconditionally do PC + 4 here
// or if the commit stage is halted, just take the current pc of the
// instruction in the commit stage
// TODO(zarubaf) This adder can at least be merged with the one in the csr_regfile stage
if (set_pc_commit_i) begin
npc_d = pc_commit_i + {{riscv::VLEN-3{1'b0}}, 3'b100};
npc_d = pc_commit_i + (halt_i ? '0 : {{riscv::VLEN-3{1'b0}}, 3'b100});
end
// 7. Debug
// enter debug on a hard-coded base-address
Expand Down
2 changes: 2 additions & 0 deletions core/load_store_unit.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ module load_store_unit import ariane_pkg::*; #(
input logic clk_i,
input logic rst_ni,
input logic flush_i,
input logic stall_st_pending_i,
output logic no_st_pending_o,
input logic amo_valid_commit_i,

Expand Down Expand Up @@ -251,6 +252,7 @@ module load_store_unit import ariane_pkg::*; #(
.clk_i,
.rst_ni,
.flush_i,
.stall_st_pending_i,
.no_st_pending_o,
.store_buffer_empty_o ( store_buffer_empty ),

Expand Down
3 changes: 2 additions & 1 deletion core/store_buffer.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ module store_buffer import ariane_pkg::*; #(
input logic rst_ni, // Asynchronous reset active low
input logic flush_i, // if we flush we need to pause the transactions on the memory
// otherwise we will run in a deadlock with the memory arbiter
input logic stall_st_pending_i, // Stall issuing non-speculative request
output logic no_st_pending_o, // non-speculative queue is empty (e.g.: everything is committed to the memory hierarchy)
output logic store_buffer_empty_o, // there is no store pending in neither the speculative unit or the non-speculative queue

Expand Down Expand Up @@ -161,7 +162,7 @@ module store_buffer import ariane_pkg::*; #(

// there should be no commit when we are flushing
// if the entry in the commit queue is valid and not speculative anymore we can issue this instruction
if (commit_queue_q[commit_read_pointer_q].valid) begin
if (commit_queue_q[commit_read_pointer_q].valid && !stall_st_pending_i) begin
req_port_o.data_req = 1'b1;
if (req_port_i.data_gnt) begin
// we can evict it from the commit buffer
Expand Down
2 changes: 2 additions & 0 deletions core/store_unit.sv
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@ module store_unit import ariane_pkg::*; #(
input logic clk_i, // Clock
input logic rst_ni, // Asynchronous reset active low
input logic flush_i,
input logic stall_st_pending_i,
output logic no_st_pending_o,
output logic store_buffer_empty_o,
// store unit input port
Expand Down Expand Up @@ -221,6 +222,7 @@ module store_unit import ariane_pkg::*; #(
.clk_i,
.rst_ni,
.flush_i,
.stall_st_pending_i,
.no_st_pending_o,
.store_buffer_empty_o,
.page_offset_i,
Expand Down

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