| /** |
| * Main controller of the processor |
| */ |
| |
| module brq_idu_controller #( |
| parameter bit WritebackStage = 0, |
| parameter bit BranchPredictor = 0 |
| ) ( |
| input logic clk_i, |
| input logic rst_ni, |
| |
| output logic ctrl_busy_o, // core is busy processing instrs |
| |
| // decoder related signals |
| input logic illegal_insn_i, // decoder has an invalid instr |
| input logic ecall_insn_i, // decoder has ECALL instr |
| input logic mret_insn_i, // decoder has MRET instr |
| input logic dret_insn_i, // decoder has DRET instr |
| input logic wfi_insn_i, // decoder has WFI instr |
| input logic ebrk_insn_i, // decoder has EBREAK instr |
| input logic csr_pipe_flush_i, // do CSR-related pipeline flush |
| |
| // instr from IF-ID pipeline stage |
| input logic instr_valid_i, // instr is valid |
| input logic [31:0] instr_i, // uncompressed instr data for mtval |
| input logic [15:0] instr_compressed_i, // instr compressed data for mtval |
| input logic instr_is_compressed_i, // instr is compressed |
| input logic instr_bp_taken_i, // instr was predicted taken branch |
| input logic instr_fetch_err_i, // instr has error |
| input logic instr_fetch_err_plus2_i, // instr error is x32 |
| input logic [31:0] pc_id_i, // instr address |
| |
| // to IF-ID pipeline stage |
| output logic instr_valid_clear_o, // kill instr in IF-ID reg |
| output logic id_in_ready_o, // ID stage is ready for new instr |
| output logic controller_run_o, // Controller is in standard instruction |
| // run mode |
| |
| // to prefetcher |
| output logic instr_req_o, // start fetching instructions |
| output logic pc_set_o, // jump to address set by pc_mux |
| output logic pc_set_spec_o, // speculative branch |
| output brq_pkg::pc_sel_e pc_mux_o, // IF stage fetch address selector |
| // (boot, normal, exception...) |
| output logic nt_branch_mispredict_o, // Not-taken branch in ID/EX was |
| // mispredicted (predicted taken) |
| output brq_pkg::exc_pc_sel_e exc_pc_mux_o, // IF stage selector for exception PC |
| output brq_pkg::exc_cause_e exc_cause_o, // for IF stage, CSRs |
| |
| // LSU |
| input logic [31:0] lsu_addr_last_i, // for mtval |
| input logic load_err_i, |
| input logic store_err_i, |
| output logic wb_exception_o, // Instruction in WB taking an exception |
| |
| // jump/branch signals |
| input logic branch_set_i, // branch set signal (branch definitely |
| // taken) |
| input logic branch_set_spec_i, // speculative branch signal (branch |
| // may be taken) |
| input logic branch_not_set_i, // branch is definitely not taken |
| input logic jump_set_i, // jump taken set signal |
| |
| // interrupt signals |
| input logic csr_mstatus_mie_i, // M-mode interrupt enable bit |
| input logic irq_pending_i, // interrupt request pending |
| input brq_pkg::irqs_t irqs_i, // interrupt requests qualified with |
| // mie CSR |
| input logic irq_nm_i, // non-maskeable interrupt |
| output logic nmi_mode_o, // core executing NMI handler |
| |
| // debug signals |
| input logic debug_req_i, |
| output brq_pkg::dbg_cause_e debug_cause_o, |
| output logic debug_csr_save_o, |
| output logic debug_mode_o, |
| input logic debug_single_step_i, |
| input logic debug_ebreakm_i, |
| input logic debug_ebreaku_i, |
| input logic trigger_match_i, |
| |
| output logic csr_save_if_o, |
| output logic csr_save_id_o, |
| output logic csr_save_wb_o, |
| output logic csr_restore_mret_id_o, |
| output logic csr_restore_dret_id_o, |
| output logic csr_save_cause_o, |
| output logic [31:0] csr_mtval_o, |
| input brq_pkg::priv_lvl_e priv_mode_i, |
| input logic csr_mstatus_tw_i, |
| |
| // stall & flush signals |
| input logic stall_id_i, |
| input logic stall_wb_i, |
| output logic flush_id_o, |
| input logic ready_wb_i, |
| |
| // performance monitors |
| output logic perf_jump_o, // we are executing a jump |
| // instruction (j, jr, jal, jalr) |
| output logic perf_tbranch_o, // we are executing a taken branch |
| // instruction |
| input logic fpu_busy_i |
| ); |
| import brq_pkg::*; |
| |
| // FSM state encoding |
| typedef enum logic [3:0] { |
| RESET, BOOT_SET, WAIT_SLEEP, SLEEP, FIRST_FETCH, DECODE, FLUSH, |
| IRQ_TAKEN, DBG_TAKEN_IF, DBG_TAKEN_ID |
| } ctrl_fsm_e; |
| |
| ctrl_fsm_e ctrl_fsm_cs, ctrl_fsm_ns; |
| |
| logic nmi_mode_q, nmi_mode_d; |
| logic debug_mode_q, debug_mode_d; |
| logic load_err_q, load_err_d; |
| logic store_err_q, store_err_d; |
| logic exc_req_q, exc_req_d; |
| logic illegal_insn_q, illegal_insn_d; |
| |
| // Of the various exception/fault signals, which one takes priority in FLUSH and hence controls |
| // what happens next (setting exc_cause, csr_mtval etc) |
| logic instr_fetch_err_prio; |
| logic illegal_insn_prio; |
| logic ecall_insn_prio; |
| logic ebrk_insn_prio; |
| logic store_err_prio; |
| logic load_err_prio; |
| |
| logic stall; |
| logic halt_if; |
| logic retain_id; |
| logic flush_id; |
| logic illegal_dret; |
| logic illegal_umode; |
| logic exc_req_lsu; |
| logic special_req_all; |
| logic special_req_branch; |
| logic enter_debug_mode; |
| logic ebreak_into_debug; |
| logic handle_irq; |
| |
| logic [3:0] mfip_id; |
| logic unused_irq_timer; |
| |
| logic ecall_insn; |
| logic mret_insn; |
| logic dret_insn; |
| logic wfi_insn; |
| logic ebrk_insn; |
| logic csr_pipe_flush; |
| logic instr_fetch_err; |
| |
| `ifndef SYNTHESIS |
| // synopsys translate_off |
| // make sure we are called later so that we do not generate messages for |
| // glitches |
| always_ff @(negedge clk_i) begin |
| // print warning in case of decoding errors |
| if ((ctrl_fsm_cs == DECODE) && instr_valid_i && !instr_fetch_err_i && illegal_insn_d) begin |
| $display("%t: Illegal instruction (hart %0x) at PC 0x%h: 0x%h", $time, brq_core.hart_id_i, |
| brq_idu.pc_id_i, brq_idu.instr_rdata_i); |
| end |
| end |
| // synopsys translate_on |
| `endif |
| |
| //////////////// |
| // Exceptions // |
| //////////////// |
| |
| assign load_err_d = load_err_i; |
| assign store_err_d = store_err_i; |
| |
| // Decoder doesn't take instr_valid into account, factor it in here. |
| assign ecall_insn = ecall_insn_i & instr_valid_i; |
| assign mret_insn = mret_insn_i & instr_valid_i; |
| assign dret_insn = dret_insn_i & instr_valid_i; |
| assign wfi_insn = wfi_insn_i & instr_valid_i; |
| assign ebrk_insn = ebrk_insn_i & instr_valid_i; |
| assign csr_pipe_flush = csr_pipe_flush_i & instr_valid_i; |
| assign instr_fetch_err = instr_fetch_err_i & instr_valid_i; |
| |
| // "Executing DRET outside of Debug Mode causes an illegal instruction exception." |
| // [Debug Spec v0.13.2, p.41] |
| assign illegal_dret = dret_insn & ~debug_mode_q; |
| |
| // Some instructions can only be executed in M-Mode |
| assign illegal_umode = (priv_mode_i != PRIV_LVL_M) & |
| // MRET must be in M-Mode. TW means trap WFI to M-Mode. |
| (mret_insn | (csr_mstatus_tw_i & wfi_insn)); |
| |
| // This is recorded in the illegal_insn_q flop to help timing. Specifically |
| // it is needed to break the path from brq_cs_registers/illegal_csr_insn_o |
| // to pc_set_o. Clear when controller is in FLUSH so it won't remain set |
| // once illegal instruction is handled. |
| // All terms in this expression are qualified by instr_valid_i |
| assign illegal_insn_d = (illegal_insn_i | illegal_dret | illegal_umode) & (ctrl_fsm_cs != FLUSH); |
| |
| // exception requests |
| // requests are flopped in exc_req_q. This is cleared when controller is in |
| // the FLUSH state so the cycle following exc_req_q won't remain set for an |
| // exception request that has just been handled. |
| // All terms in this expression are qualified by instr_valid_i |
| assign exc_req_d = (ecall_insn | ebrk_insn | illegal_insn_d | instr_fetch_err) & |
| (ctrl_fsm_cs != FLUSH); |
| |
| // LSU exception requests |
| assign exc_req_lsu = store_err_i | load_err_i; |
| |
| |
| // special requests: special instructions, pipeline flushes, exceptions... |
| |
| // To avoid creating a path from data_err_i -> instr_req_o and to help timing the below |
| // special_req_all has a version that only applies to branches. For a branch the controller needs |
| // to set pc_set_o but only if there is no special request. If the generic special_req_all signal |
| // is used then a variety of signals that will never cause a special request during a branch |
| // instruction end up factored into pc_set_o. The special_req_branch only considers the special |
| // request reasons that are relevant to a branch. |
| |
| // generic special request signal, applies to all instructions |
| // All terms in this expression are qualified by instr_valid_i except exc_req_lsu which can come |
| // from the Writeback stage with no instr_valid_i from the ID stage |
| assign special_req_all = mret_insn | dret_insn | wfi_insn | csr_pipe_flush | |
| exc_req_d | exc_req_lsu; |
| |
| // special request that can specifically occur during branch instructions |
| // All terms in this expression are qualified by instr_valid_i |
| assign special_req_branch = instr_fetch_err & (ctrl_fsm_cs != FLUSH); |
| |
| |
| // Exception/fault prioritisation is taken from Table 3.7 of Priviledged Spec v1.11 |
| if (WritebackStage) begin : g_wb_exceptions |
| always_comb begin |
| instr_fetch_err_prio = 0; |
| illegal_insn_prio = 0; |
| ecall_insn_prio = 0; |
| ebrk_insn_prio = 0; |
| store_err_prio = 0; |
| load_err_prio = 0; |
| |
| // Note that with the writeback stage store/load errors occur on the instruction in writeback, |
| // all other exception/faults occur on the instruction in ID/EX. The faults from writeback |
| // must take priority as that instruction is architecurally ordered before the one in ID/EX. |
| if (store_err_q) begin |
| store_err_prio = 1'b1; |
| end else if (load_err_q) begin |
| load_err_prio = 1'b1; |
| end else if (instr_fetch_err) begin |
| instr_fetch_err_prio = 1'b1; |
| end else if (illegal_insn_q) begin |
| illegal_insn_prio = 1'b1; |
| end else if (ecall_insn) begin |
| ecall_insn_prio = 1'b1; |
| end else if (ebrk_insn) begin |
| ebrk_insn_prio = 1'b1; |
| end |
| end |
| |
| // Instruction in writeback is generating an exception so instruction in ID must not execute |
| assign wb_exception_o = load_err_q | store_err_q | load_err_i | store_err_i; |
| end else begin : g_no_wb_exceptions |
| always_comb begin |
| instr_fetch_err_prio = 0; |
| illegal_insn_prio = 0; |
| ecall_insn_prio = 0; |
| ebrk_insn_prio = 0; |
| store_err_prio = 0; |
| load_err_prio = 0; |
| |
| if (instr_fetch_err) begin |
| instr_fetch_err_prio = 1'b1; |
| end else if (illegal_insn_q) begin |
| illegal_insn_prio = 1'b1; |
| end else if (ecall_insn) begin |
| ecall_insn_prio = 1'b1; |
| end else if (ebrk_insn) begin |
| ebrk_insn_prio = 1'b1; |
| end else if (store_err_q) begin |
| store_err_prio = 1'b1; |
| end else if (load_err_q) begin |
| load_err_prio = 1'b1; |
| end |
| end |
| assign wb_exception_o = 1'b0; |
| end |
| |
| |
| //////////////// |
| // Interrupts // |
| //////////////// |
| |
| // Enter debug mode due to an external debug_req_i or because the core is in |
| // single step mode (dcsr.step == 1). Single step must be qualified with |
| // instruction valid otherwise the core will immediately enter debug mode |
| // due to a recently flushed IF (or a delay in an instruction returning from |
| // memory) before it has had anything to single step. |
| // Also enter debug mode on a trigger match (hardware breakpoint) |
| assign enter_debug_mode = (debug_req_i | (debug_single_step_i & instr_valid_i) | |
| trigger_match_i) & ~debug_mode_q; |
| |
| // Set when an ebreak should enter debug mode rather than jump to exception |
| // handler |
| assign ebreak_into_debug = priv_mode_i == PRIV_LVL_M ? debug_ebreakm_i : |
| priv_mode_i == PRIV_LVL_U ? debug_ebreaku_i : |
| 1'b0; |
| |
| // Interrupts including NMI are ignored, |
| // - while in debug mode [Debug Spec v0.13.2, p.39], |
| // - while in NMI mode (nested NMIs are not supported, NMI has highest priority and |
| // cannot be interrupted by regular interrupts). |
| assign handle_irq = ~debug_mode_q & ~nmi_mode_q & |
| (irq_nm_i | (irq_pending_i & csr_mstatus_mie_i)); |
| |
| // generate ID of fast interrupts, highest priority to highest ID |
| always_comb begin : gen_mfip_id |
| if (irqs_i.irq_fast[14]) mfip_id = 4'd14; |
| else if (irqs_i.irq_fast[13]) mfip_id = 4'd13; |
| else if (irqs_i.irq_fast[12]) mfip_id = 4'd12; |
| else if (irqs_i.irq_fast[11]) mfip_id = 4'd11; |
| else if (irqs_i.irq_fast[10]) mfip_id = 4'd10; |
| else if (irqs_i.irq_fast[ 9]) mfip_id = 4'd9; |
| else if (irqs_i.irq_fast[ 8]) mfip_id = 4'd8; |
| else if (irqs_i.irq_fast[ 7]) mfip_id = 4'd7; |
| else if (irqs_i.irq_fast[ 6]) mfip_id = 4'd6; |
| else if (irqs_i.irq_fast[ 5]) mfip_id = 4'd5; |
| else if (irqs_i.irq_fast[ 4]) mfip_id = 4'd4; |
| else if (irqs_i.irq_fast[ 3]) mfip_id = 4'd3; |
| else if (irqs_i.irq_fast[ 2]) mfip_id = 4'd2; |
| else if (irqs_i.irq_fast[ 1]) mfip_id = 4'd1; |
| else mfip_id = 4'd0; |
| end |
| |
| assign unused_irq_timer = irqs_i.irq_timer; |
| |
| ///////////////////// |
| // Core controller // |
| ///////////////////// |
| |
| always_comb begin |
| // Default values |
| instr_req_o = 1'b1; |
| |
| csr_save_if_o = 1'b0; |
| csr_save_id_o = 1'b0; |
| csr_save_wb_o = 1'b0; |
| csr_restore_mret_id_o = 1'b0; |
| csr_restore_dret_id_o = 1'b0; |
| csr_save_cause_o = 1'b0; |
| csr_mtval_o = '0; |
| |
| // The values of pc_mux and exc_pc_mux are only relevant if pc_set is set. Some of the states |
| // below always set pc_mux and exc_pc_mux but only set pc_set if certain conditions are met. |
| // This avoid having to factor those conditions into the pc_mux and exc_pc_mux select signals |
| // helping timing. |
| pc_mux_o = PC_BOOT; |
| pc_set_o = 1'b0; |
| pc_set_spec_o = 1'b0; |
| nt_branch_mispredict_o = 1'b0; |
| |
| exc_pc_mux_o = EXC_PC_IRQ; |
| exc_cause_o = EXC_CAUSE_INSN_ADDR_MISA; // = 6'h00 |
| |
| ctrl_fsm_ns = ctrl_fsm_cs; |
| |
| ctrl_busy_o = 1'b1; |
| |
| halt_if = 1'b0; |
| retain_id = 1'b0; |
| flush_id = 1'b0; |
| |
| debug_csr_save_o = 1'b0; |
| debug_cause_o = DBG_CAUSE_EBREAK; |
| debug_mode_d = debug_mode_q; |
| nmi_mode_d = nmi_mode_q; |
| |
| perf_tbranch_o = 1'b0; |
| perf_jump_o = 1'b0; |
| |
| controller_run_o = 1'b0; |
| |
| unique case (ctrl_fsm_cs) |
| RESET: begin |
| instr_req_o = 1'b0; |
| pc_mux_o = PC_BOOT; |
| pc_set_o = 1'b1; |
| pc_set_spec_o = 1'b1; |
| ctrl_fsm_ns = BOOT_SET; |
| end |
| |
| BOOT_SET: begin |
| // copy boot address to instr fetch address |
| instr_req_o = 1'b1; |
| pc_mux_o = PC_BOOT; |
| pc_set_o = 1'b1; |
| pc_set_spec_o = 1'b1; |
| |
| ctrl_fsm_ns = FIRST_FETCH; |
| end |
| |
| WAIT_SLEEP: begin |
| ctrl_busy_o = 1'b0; |
| instr_req_o = 1'b0; |
| halt_if = 1'b1; |
| flush_id = 1'b1; |
| ctrl_fsm_ns = SLEEP; |
| end |
| |
| SLEEP: begin |
| // instruction in IF stage is already valid |
| // we begin execution when an interrupt has arrived |
| instr_req_o = 1'b0; |
| halt_if = 1'b1; |
| flush_id = 1'b1; |
| |
| // normal execution flow |
| // in debug mode or single step mode we leave immediately (wfi=nop) |
| if (irq_nm_i || irq_pending_i || debug_req_i || debug_mode_q || debug_single_step_i) begin |
| ctrl_fsm_ns = FIRST_FETCH; |
| end else begin |
| // Make sure clock remains disabled. |
| ctrl_busy_o = 1'b0; |
| end |
| end |
| |
| FIRST_FETCH: begin |
| // Stall because of IF miss |
| if (id_in_ready_o) begin |
| ctrl_fsm_ns = DECODE; |
| end |
| |
| // handle interrupts |
| if (handle_irq) begin |
| // We are handling an interrupt. Set halt_if to tell IF not to give |
| // us any more instructions before it redirects to the handler, but |
| // don't set flush_id: we must allow this instruction to complete |
| // (since it might have outstanding loads or stores). |
| ctrl_fsm_ns = IRQ_TAKEN; |
| halt_if = 1'b1; |
| end |
| |
| // enter debug mode |
| if (enter_debug_mode) begin |
| ctrl_fsm_ns = DBG_TAKEN_IF; |
| // Halt IF only for now, ID will be flushed in DBG_TAKEN_IF as the |
| // ID state is needed for correct debug mode entry |
| halt_if = 1'b1; |
| end |
| end |
| |
| DECODE: begin |
| // normal operating mode of the ID stage, in case of debug and interrupt requests, |
| // priorities are as follows (lower number == higher priority) |
| // 1. currently running (multicycle) instructions and exceptions caused by these |
| // 2. debug requests |
| // 3. interrupt requests |
| |
| controller_run_o = 1'b1; |
| |
| // Set PC mux for branch and jump here to ease timing. Value is only relevant if pc_set_o is |
| // also set. Setting the mux value here avoids factoring in special_req and instr_valid_i |
| // which helps timing. |
| pc_mux_o = PC_JUMP; |
| |
| |
| // Get ready for special instructions, exceptions, pipeline flushes |
| if (special_req_all) begin |
| // Halt IF but don't flush ID. This leaves a valid instruction in |
| // ID so controller can determine appropriate action in the |
| // FLUSH state. |
| retain_id = 1'b1; |
| |
| // Wait for the writeback stage to either be ready for a new instruction or raise its own |
| // exception before going to FLUSH. If the instruction in writeback raises an exception it |
| // must take priority over any exception from an instruction in ID/EX. Only once the |
| // writeback stage is ready can we be certain that won't happen. Without a writeback |
| // stage ready_wb_i == 1 so the FSM will always go directly to FLUSH. |
| |
| if (ready_wb_i | wb_exception_o) begin |
| ctrl_fsm_ns = FLUSH; |
| end |
| end |
| |
| if (!special_req_branch) begin |
| if (branch_set_i || jump_set_i) begin |
| // Only set the PC if the branch predictor hasn't already done the branch for us |
| pc_set_o = BranchPredictor ? ~instr_bp_taken_i : 1'b1; |
| |
| perf_tbranch_o = branch_set_i; |
| perf_jump_o = jump_set_i; |
| end |
| |
| if (BranchPredictor) begin |
| if (instr_bp_taken_i & branch_not_set_i) begin |
| // If the instruction is a branch that was predicted to be taken but was not taken |
| // signal a mispredict. |
| nt_branch_mispredict_o = 1'b1; |
| end |
| end |
| end |
| |
| // pc_set signal excluding branch taken condition |
| if ((branch_set_spec_i || jump_set_i) && !special_req_branch) begin |
| // Only speculatively set the PC if the branch predictor hasn't already done the branch |
| // for us |
| pc_set_spec_o = BranchPredictor ? ~instr_bp_taken_i : 1'b1; |
| end |
| |
| // If entering debug mode or handling an IRQ the core needs to wait |
| // until the current instruction has finished executing. Stall IF |
| // during that time. |
| if ((enter_debug_mode || handle_irq) && stall) begin |
| halt_if = 1'b1; |
| end |
| |
| if (!stall && !special_req_all) begin |
| if (enter_debug_mode) begin |
| // enter debug mode |
| ctrl_fsm_ns = DBG_TAKEN_IF; |
| // Halt IF only for now, ID will be flushed in DBG_TAKEN_IF as the |
| // ID state is needed for correct debug mode entry |
| halt_if = 1'b1; |
| end else if (handle_irq) begin |
| // handle interrupt (not in debug mode) |
| ctrl_fsm_ns = IRQ_TAKEN; |
| // We are handling an interrupt (not in debug mode). Set halt_if to |
| // tell IF not to give us any more instructions before it redirects |
| // to the handler, but don't set flush_id: we must allow this |
| // instruction to complete (since it might have outstanding loads |
| // or stores). |
| halt_if = 1'b1; |
| end |
| end |
| |
| end // DECODE |
| |
| IRQ_TAKEN: begin |
| pc_mux_o = PC_EXC; |
| exc_pc_mux_o = EXC_PC_IRQ; |
| |
| if (handle_irq) begin |
| pc_set_o = 1'b1; |
| pc_set_spec_o = 1'b1; |
| |
| csr_save_if_o = 1'b1; |
| csr_save_cause_o = 1'b1; |
| |
| // interrupt priorities according to Privileged Spec v1.11 p.31 |
| if (irq_nm_i && !nmi_mode_q) begin |
| exc_cause_o = EXC_CAUSE_IRQ_NM; |
| nmi_mode_d = 1'b1; // enter NMI mode |
| end else if (irqs_i.irq_fast != 15'b0) begin |
| // generate exception cause ID from fast interrupt ID: |
| // - first bit distinguishes interrupts from exceptions, |
| // - second bit adds 16 to fast interrupt ID |
| // for example EXC_CAUSE_IRQ_FAST_0 = {1'b1, 5'd16} |
| exc_cause_o = exc_cause_e'({2'b11, mfip_id}); |
| end else if (irqs_i.irq_external) begin |
| exc_cause_o = EXC_CAUSE_IRQ_EXTERNAL_M; |
| end else if (irqs_i.irq_software) begin |
| exc_cause_o = EXC_CAUSE_IRQ_SOFTWARE_M; |
| end else begin // irqs_i.irq_timer |
| exc_cause_o = EXC_CAUSE_IRQ_TIMER_M; |
| end |
| end |
| |
| ctrl_fsm_ns = DECODE; |
| end |
| |
| DBG_TAKEN_IF: begin |
| pc_mux_o = PC_EXC; |
| exc_pc_mux_o = EXC_PC_DBD; |
| |
| // enter debug mode and save PC in IF to dpc |
| // jump to debug exception handler in debug memory |
| if (debug_single_step_i || debug_req_i || trigger_match_i) begin |
| flush_id = 1'b1; |
| pc_set_o = 1'b1; |
| pc_set_spec_o = 1'b1; |
| |
| csr_save_if_o = 1'b1; |
| debug_csr_save_o = 1'b1; |
| |
| csr_save_cause_o = 1'b1; |
| if (trigger_match_i) begin |
| debug_cause_o = DBG_CAUSE_TRIGGER; |
| end else if (debug_single_step_i) begin |
| debug_cause_o = DBG_CAUSE_STEP; |
| end else begin |
| debug_cause_o = DBG_CAUSE_HALTREQ; |
| end |
| |
| // enter debug mode |
| debug_mode_d = 1'b1; |
| end |
| |
| ctrl_fsm_ns = DECODE; |
| end |
| |
| DBG_TAKEN_ID: begin |
| // enter debug mode and save PC in ID to dpc, used when encountering |
| // 1. EBREAK during debug mode |
| // 2. EBREAK with forced entry into debug mode (ebreakm or ebreaku set). |
| // regular ebreak's go through FLUSH. |
| // |
| // for 1. do not update dcsr and dpc, for 2. do so [Debug Spec v0.13.2, p.39] |
| // jump to debug exception handler in debug memory |
| flush_id = 1'b1; |
| pc_mux_o = PC_EXC; |
| pc_set_o = 1'b1; |
| pc_set_spec_o = 1'b1; |
| exc_pc_mux_o = EXC_PC_DBD; |
| |
| // update dcsr and dpc |
| if (ebreak_into_debug && !debug_mode_q) begin // ebreak with forced entry |
| |
| // dpc (set to the address of the EBREAK, i.e. set to PC in ID stage) |
| csr_save_cause_o = 1'b1; |
| csr_save_id_o = 1'b1; |
| |
| // dcsr |
| debug_csr_save_o = 1'b1; |
| debug_cause_o = DBG_CAUSE_EBREAK; |
| end |
| |
| // enter debug mode |
| debug_mode_d = 1'b1; |
| |
| ctrl_fsm_ns = DECODE; |
| end |
| |
| FLUSH: begin |
| // flush the pipeline |
| halt_if = 1'b1; |
| flush_id = 1'b1; |
| ctrl_fsm_ns = DECODE; |
| |
| // As pc_mux and exc_pc_mux can take various values in this state they aren't set early |
| // here. |
| |
| // exceptions: set exception PC, save PC and exception cause |
| // exc_req_lsu is high for one clock cycle only (in DECODE) |
| if (exc_req_q || store_err_q || load_err_q) begin |
| pc_set_o = 1'b1; |
| pc_set_spec_o = 1'b1; |
| pc_mux_o = PC_EXC; |
| exc_pc_mux_o = debug_mode_q ? EXC_PC_DBG_EXC : EXC_PC_EXC; |
| |
| if (WritebackStage) begin : g_writeback_mepc_save |
| // With the writeback stage present whether an instruction accessing memory will cause |
| // an exception is only known when it is in writeback. So when taking such an exception |
| // epc must come from writeback. |
| csr_save_id_o = ~(store_err_q | load_err_q); |
| csr_save_wb_o = store_err_q | load_err_q; |
| end else begin : g_no_writeback_mepc_save |
| csr_save_id_o = 1'b0; |
| end |
| |
| csr_save_cause_o = 1'b1; |
| |
| // Exception/fault prioritisation logic will have set exactly 1 X_prio signal |
| unique case (1'b1) |
| instr_fetch_err_prio: begin |
| exc_cause_o = EXC_CAUSE_INSTR_ACCESS_FAULT; |
| csr_mtval_o = instr_fetch_err_plus2_i ? (pc_id_i + 32'd2) : pc_id_i; |
| end |
| illegal_insn_prio: begin |
| exc_cause_o = EXC_CAUSE_ILLEGAL_INSN; |
| csr_mtval_o = instr_is_compressed_i ? {16'b0, instr_compressed_i} : instr_i; |
| end |
| ecall_insn_prio: begin |
| exc_cause_o = (priv_mode_i == PRIV_LVL_M) ? EXC_CAUSE_ECALL_MMODE : |
| EXC_CAUSE_ECALL_UMODE; |
| end |
| ebrk_insn_prio: begin |
| if (debug_mode_q | ebreak_into_debug) begin |
| /* |
| * EBREAK in debug mode re-enters debug mode |
| * |
| * "The only exception is EBREAK. When that is executed in Debug |
| * Mode, it halts the hart again but without updating dpc or |
| * dcsr." [Debug Spec v0.13.2, p.39] |
| */ |
| |
| /* |
| * dcsr.ebreakm == 1: |
| * "EBREAK instructions in M-mode enter Debug Mode." |
| * [Debug Spec v0.13.2, p.42] |
| */ |
| pc_set_o = 1'b0; |
| pc_set_spec_o = 1'b0; |
| csr_save_id_o = 1'b0; |
| csr_save_cause_o = 1'b0; |
| ctrl_fsm_ns = DBG_TAKEN_ID; |
| flush_id = 1'b0; |
| end else begin |
| /* |
| * "The EBREAK instruction is used by debuggers to cause control |
| * to be transferred back to a debugging environment. It |
| * generates a breakpoint exception and performs no other |
| * operation. [...] ECALL and EBREAK cause the receiving |
| * privilege mode's epc register to be set to the address of the |
| * ECALL or EBREAK instruction itself, not the address of the |
| * following instruction." [Privileged Spec v1.11, p.40] |
| */ |
| exc_cause_o = EXC_CAUSE_BREAKPOINT; |
| end |
| end |
| store_err_prio: begin |
| exc_cause_o = EXC_CAUSE_STORE_ACCESS_FAULT; |
| csr_mtval_o = lsu_addr_last_i; |
| end |
| load_err_prio: begin |
| exc_cause_o = EXC_CAUSE_LOAD_ACCESS_FAULT; |
| csr_mtval_o = lsu_addr_last_i; |
| end |
| default: ; |
| endcase |
| end else begin |
| // special instructions and pipeline flushes |
| if (mret_insn) begin |
| pc_mux_o = PC_ERET; |
| pc_set_o = 1'b1; |
| pc_set_spec_o = 1'b1; |
| csr_restore_mret_id_o = 1'b1; |
| if (nmi_mode_q) begin |
| nmi_mode_d = 1'b0; // exit NMI mode |
| end |
| end else if (dret_insn) begin |
| pc_mux_o = PC_DRET; |
| pc_set_o = 1'b1; |
| pc_set_spec_o = 1'b1; |
| debug_mode_d = 1'b0; |
| csr_restore_dret_id_o = 1'b1; |
| end else if (wfi_insn) begin |
| ctrl_fsm_ns = WAIT_SLEEP; |
| end else if (csr_pipe_flush && handle_irq) begin |
| // start handling IRQs when doing CSR-related pipeline flushes |
| ctrl_fsm_ns = IRQ_TAKEN; |
| end |
| end // exc_req_q |
| |
| // Entering debug mode due to either single step or debug_req. Ensure |
| // registers are set for exception but then enter debug handler rather |
| // than exception handler [Debug Spec v0.13.2, p.44] |
| // Leave all other signals as is to ensure CSRs and PC get set as if |
| // core was entering exception handler, entry to debug mode will then |
| // see the appropriate state and setup dpc correctly. |
| // If an EBREAK instruction is causing us to enter debug mode on the |
| // same cycle as a debug_req or single step, honor the EBREAK and |
| // proceed to DBG_TAKEN_ID. |
| if (enter_debug_mode && !(ebrk_insn_prio && ebreak_into_debug)) begin |
| ctrl_fsm_ns = DBG_TAKEN_IF; |
| end |
| end // FLUSH |
| |
| default: begin |
| instr_req_o = 1'b0; |
| ctrl_fsm_ns = RESET; |
| end |
| endcase |
| end |
| |
| assign flush_id_o = flush_id; |
| |
| // signal to CSR when in debug mode |
| assign debug_mode_o = debug_mode_q; |
| |
| // signal to CSR when in an NMI handler (for nested exception handling) |
| assign nmi_mode_o = nmi_mode_q; |
| |
| /////////////////// |
| // Stall control // |
| /////////////////// |
| |
| // If high current instruction cannot complete this cycle. Either because it needs more cycles to |
| // finish (stall_id_i) or because the writeback stage cannot accept it yet (stall_wb_i). If there |
| // is no writeback stage stall_wb_i is a constant 0. |
| assign stall = stall_id_i | stall_wb_i | fpu_busy_i; |
| |
| // signal to IF stage that ID stage is ready for next instr |
| assign id_in_ready_o = ~stall & ~halt_if & ~retain_id; |
| |
| // kill instr in IF-ID pipeline reg that are done, or if a |
| // multicycle instr causes an exception for example |
| // retain_id is another kind of stall, where the instr_valid bit must remain |
| // set (unless flush_id is set also). It cannot be factored directly into |
| // stall as this causes a combinational loop. |
| assign instr_valid_clear_o = ~(stall | retain_id) | flush_id; |
| |
| // update registers |
| always_ff @(posedge clk_i or negedge rst_ni) begin : update_regs |
| if (!rst_ni) begin |
| ctrl_fsm_cs <= RESET; |
| nmi_mode_q <= 1'b0; |
| debug_mode_q <= 1'b0; |
| load_err_q <= 1'b0; |
| store_err_q <= 1'b0; |
| exc_req_q <= 1'b0; |
| illegal_insn_q <= 1'b0; |
| end else begin |
| ctrl_fsm_cs <= ctrl_fsm_ns; |
| nmi_mode_q <= nmi_mode_d; |
| debug_mode_q <= debug_mode_d; |
| load_err_q <= load_err_d; |
| store_err_q <= store_err_d; |
| exc_req_q <= exc_req_d; |
| illegal_insn_q <= illegal_insn_d; |
| end |
| end |
| |
| |
| |
| endmodule |
