lowRISC · SamuelRiedel · Apr 24, 2026 · Apr 24, 2026 · Apr 27, 2026 · Apr 27, 2026
diff --git a/dv/cosim/cosim.h b/dv/cosim/cosim.h
@@ -128,6 +128,17 @@ class Cosim {
   // A full 64-bit value is provided setting both the mcycle and mcycleh CSRs.
   virtual void set_mcycle(uint64_t mcycle) = 0;
 
+  // Set the value of minstret.
+  //
+  // The co-simulation model doesn't alter the value of minstret itself (other
+  // than instructions that do a direct CSR write). minstret should be set to
+  // the correct value before any `step` call that may execute an instruction
+  // that observes the value of minstret.
+  //
+  // A full 64-bit value is provided setting both the minstret and minstreth
+  // CSRs.
+  virtual void set_minstret(uint64_t minstret) = 0;
+
   // Set the value of a CSR. This is used when it is needed to have direct
   // communication between DUT and Spike (e.g. Performance counters).
   virtual void set_csr(const int csr_num, const uint32_t new_val) = 0;

diff --git a/dv/cosim/cosim_dpi.cc b/dv/cosim/cosim_dpi.cc
@@ -52,6 +52,13 @@ void riscv_cosim_set_mcycle(Cosim *cosim, svBitVecVal *mcycle) {
   cosim->set_mcycle(mcycle_full);
 }
 
+void riscv_cosim_set_minstret(Cosim *cosim, svBitVecVal *minstret) {
+  assert(cosim);
+
+  uint64_t minstret_full = minstret[0] | (uint64_t)minstret[1] << 32;
+  cosim->set_minstret(minstret_full);
+}
+
 void riscv_cosim_set_csr(Cosim *cosim, const int csr_id,
                          const svBitVecVal *csr_val) {
   assert(cosim);

diff --git a/dv/cosim/cosim_dpi.h b/dv/cosim/cosim_dpi.h
@@ -23,6 +23,7 @@ void riscv_cosim_set_nmi(Cosim *cosim, svBit nmi);
 void riscv_cosim_set_nmi_int(Cosim *cosim, svBit nmi_int);
 void riscv_cosim_set_debug_req(Cosim *cosim, svBit debug_req);
 void riscv_cosim_set_mcycle(Cosim *cosim, svBitVecVal *mcycle);
+void riscv_cosim_set_minstret(Cosim *cosim, svBitVecVal *minstret);
 void riscv_cosim_set_csr(Cosim *cosim, const int csr_id,
                          const svBitVecVal *csr_val);
 void riscv_cosim_set_ic_scr_key_valid(Cosim *cosim, svBit valid);

diff --git a/dv/cosim/cosim_dpi.svh b/dv/cosim/cosim_dpi.svh
@@ -18,6 +18,7 @@ import "DPI-C" function void riscv_cosim_set_nmi(chandle cosim_handle, bit nmi);
 import "DPI-C" function void riscv_cosim_set_nmi_int(chandle cosim_handle, bit nmi_int);
 import "DPI-C" function void riscv_cosim_set_debug_req(chandle cosim_handle, bit debug_req);
 import "DPI-C" function void riscv_cosim_set_mcycle(chandle cosim_handle, bit [63:0] mcycle);
+import "DPI-C" function void riscv_cosim_set_minstret(chandle cosim_handle, bit [63:0] minstret);
 import "DPI-C" function void riscv_cosim_set_csr(chandle cosim_handle, int csr_id,
   bit [31:0] csr_val);
 import "DPI-C" function void riscv_cosim_set_ic_scr_key_valid(chandle cosim_handle, bit valid);

diff --git a/dv/cosim/spike_cosim.cc b/dv/cosim/spike_cosim.cc
@@ -39,7 +39,10 @@ SpikeCosim::SpikeCosim(const std::string &isa_string, uint32_t start_pc,
                        uint32_t pmp_num_regions, uint32_t pmp_granularity,
                        uint32_t mhpm_counter_num, uint32_t dm_start_addr,
                        uint32_t dm_end_addr)
-    : nmi_mode(false), pending_iside_error(false), insn_cnt(0) {
+    : nmi_mode(false),
+      pending_iside_error(false),
+      insn_cnt(0),
+      mhpm_counter_num(mhpm_counter_num) {
   FILE *log_file = nullptr;
   if (trace_log_path.length() != 0) {
     log = std::make_unique<log_file_t>(trace_log_path.c_str());
@@ -747,6 +750,27 @@ void SpikeCosim::set_mcycle(uint64_t mcycle) {
   // to write all 64 bits at once at least.
 }
 
+void SpikeCosim::set_minstret(uint64_t minstret) {
+  uint32_t upper_minstret = minstret >> 32;
+  uint32_t lower_minstret = minstret & 0xffffffff;
+
+  // Spike decrements the MINSTRET CSR when you write to it. This is the same
+  // issue as with MCYCLE. See `set_mcycle` for more details.
+
+  // Write the lower half first, incremented twice due to the double decrement
+  processor->get_state()->csrmap[CSR_MINSTRET]->write(lower_minstret + 2);
+
+  if ((processor->get_state()->csrmap[CSR_MINSTRET]->read() & 0xffffffff) ==
+      0) {
+    // If the lower half is 0 at this point then the upper half will get
+    // decremented, so increment it first.
+    upper_minstret++;
+  }
+
+  // Set the upper half
+  processor->get_state()->csrmap[CSR_MINSTRETH]->write(upper_minstret);
+}
+
 void SpikeCosim::set_csr(const int csr_num, const uint32_t new_val) {
   // Note that this is tested with ibex-cosim-v0.3 version of Spike. 'set_csr'
   // method might have a hardwired zero for mhpmcounterX registers.
@@ -832,6 +856,19 @@ void SpikeCosim::fixup_csr(int csr_num, uint32_t csr_val) {
       processor->set_csr(csr_num, new_val);
 #else
       processor->put_csr(csr_num, new_val);
+#endif
+      break;
+    }
+    case CSR_MCOUNTEREN: {
+      // Bits 3..3+mhpm_counter_num-1 correspond to implemented HPM counters
+      reg_t hpm_mask = ((1 << mhpm_counter_num) - 1) << 3;
+      // Bit 0 and 2 are for mcycle and minstret which are always implemented
+      // Bit 1 is for time which is not implemented, hence the mask 0x5
+      reg_t new_val = csr_val & (0x5 | hpm_mask);
+#ifdef OLD_SPIKE
+      processor->set_csr(csr_num, new_val);
+#else
+      processor->put_csr(csr_num, new_val);
 #endif
       break;
     }

diff --git a/dv/cosim/spike_cosim.h b/dv/cosim/spike_cosim.h
@@ -98,6 +98,7 @@ class SpikeCosim : public simif_t, public Cosim {
   void misaligned_pmp_fixup();
 
   unsigned int insn_cnt;
+  uint32_t mhpm_counter_num;
 
  public:
   SpikeCosim(const std::string &isa_string, uint32_t start_pc,
@@ -131,6 +132,7 @@ class SpikeCosim : public simif_t, public Cosim {
   void set_nmi_int(bool nmi_int) override;
   void set_debug_req(bool debug_req) override;
   void set_mcycle(uint64_t mcycle) override;
+  void set_minstret(uint64_t minstret) override;
   void set_csr(const int csr_num, const uint32_t new_val) override;
   void set_ic_scr_key_valid(bool valid) override;
   void notify_dside_access(const DSideAccessInfo &access_info) override;

diff --git a/dv/formal/check/top.sv b/dv/formal/check/top.sv
@@ -103,6 +103,7 @@ module top import ibex_pkg::*; #(
 
   // CPU Control Signals
   input  ibex_mubi_t                                                   fetch_enable_i,
+  input  ibex_mubi_t                                                   mcounteren_writable_i,
   output logic                                                         core_sleep_o,
   output logic                                                         alert_minor_o,
   output logic                                                         alert_major_internal_o,

diff --git a/dv/riscv_compliance/rtl/ibex_riscv_compliance.sv b/dv/riscv_compliance/rtl/ibex_riscv_compliance.sv
@@ -216,6 +216,7 @@ module ibex_riscv_compliance (
       .double_fault_seen_o       (                     ),
 
       .fetch_enable_i            (ibex_pkg::IbexMuBiOn ),
+      .mcounteren_writable_i     (ibex_pkg::IbexMuBiOn ),
       .alert_minor_o             (                     ),
       .alert_major_internal_o    (                     ),
       .alert_major_bus_o         (                     ),

diff --git a/dv/uvm/core_ibex/common/ibex_cosim_agent/ibex_cosim_scoreboard.sv b/dv/uvm/core_ibex/common/ibex_cosim_agent/ibex_cosim_scoreboard.sv
@@ -151,6 +151,7 @@ class ibex_cosim_scoreboard extends uvm_scoreboard;
       riscv_cosim_set_nmi_int(cosim_handle, rvfi_instr.nmi_int);
       riscv_cosim_set_mip(cosim_handle, rvfi_instr.pre_mip, rvfi_instr.post_mip);
       riscv_cosim_set_mcycle(cosim_handle, rvfi_instr.mcycle);
+      riscv_cosim_set_minstret(cosim_handle, rvfi_instr.minstret);
 
       // Set performance counters through a pseudo-backdoor write
       for (int i=0; i < 10; i++) begin

diff --git a/dv/uvm/core_ibex/common/ibex_cosim_agent/ibex_rvfi_monitor.sv b/dv/uvm/core_ibex/common/ibex_cosim_agent/ibex_rvfi_monitor.sv
@@ -44,6 +44,7 @@ class ibex_rvfi_monitor extends uvm_monitor;
       trans_collected.debug_req        = vif.monitor_cb.ext_debug_req;
       trans_collected.rf_wr_suppress   = vif.monitor_cb.ext_rf_wr_suppress;
       trans_collected.mcycle           = vif.monitor_cb.ext_mcycle;
+      trans_collected.minstret         = vif.monitor_cb.ext_minstret;
       trans_collected.ic_scr_key_valid = vif.monitor_cb.ext_ic_scr_key_valid;
 
       for (int i=0; i < 10; i++) begin

diff --git a/dv/uvm/core_ibex/common/ibex_cosim_agent/ibex_rvfi_seq_item.sv b/dv/uvm/core_ibex/common/ibex_cosim_agent/ibex_rvfi_seq_item.sv
@@ -16,6 +16,7 @@ class ibex_rvfi_seq_item extends uvm_sequence_item;
   bit        debug_req;
   bit        rf_wr_suppress;
   bit [63:0] mcycle;
+  bit [63:0] minstret;
 
   bit [31:0] mhpmcounters  [10];
   bit [31:0] mhpmcountersh [10];
@@ -34,6 +35,7 @@ class ibex_rvfi_seq_item extends uvm_sequence_item;
     `uvm_field_int (debug_req, UVM_DEFAULT)
     `uvm_field_int (rf_wr_suppress, UVM_DEFAULT)
     `uvm_field_int (mcycle, UVM_DEFAULT)
+    `uvm_field_int (minstret, UVM_DEFAULT)
     `uvm_field_sarray_int (mhpmcounters, UVM_DEFAULT)
     `uvm_field_sarray_int (mhpmcountersh, UVM_DEFAULT)
     `uvm_field_int (ic_scr_key_valid, UVM_DEFAULT)