Add mcounteren register

rtl/ibex_cs_registers.sv

@@ -258,6 +258,11 @@ module ibex_cs_registers import ibex_pkg::*; #(
   logic [MHPMCounterNum+3-1:0] mcountinhibit_d, mcountinhibit_q;
   logic                        mcountinhibit_we;
 
+  // mcounteren: machine counter enable (controls U-mode counter access)
+  logic [31:0]                 mcounteren;
+  logic [MHPMCounterNum+3-1:0] mcounteren_d, mcounteren_q;
+  logic                        mcounteren_we;
+
   // mhpmcounter flops are elaborated below providing only the precise number that is required based
   // on MHPMCounterNum/MHPMCounterWidth. This signal connects to the Q output of these flops
   // where they exist and is otherwise 0.
@@ -374,9 +379,7 @@ module ibex_cs_registers import ibex_pkg::*; #(
       end
 
       // mcounteren: machine counter enable
-      CSR_MCOUNTEREN: begin
-        csr_rdata_int = '0;
-      end
+      CSR_MCOUNTEREN: csr_rdata_int = mcounteren;
 
       CSR_MSCRATCH: csr_rdata_int = mscratch_q;
 
@@ -598,6 +601,7 @@ module ibex_cs_registers import ibex_pkg::*; #(
     mstack_cause_d = mcause_q;
 
     mcountinhibit_we = 1'b0;
+    mcounteren_we    = 1'b0;
     mhpmcounter_we   = '0;
     mhpmcounterh_we  = '0;
 
@@ -675,6 +679,7 @@ module ibex_cs_registers import ibex_pkg::*; #(
         CSR_DSCRATCH1: dscratch1_en = 1'b1;
 
         // machine counter/timers
+        CSR_MCOUNTEREN:    mcounteren_we    = 1'b1;
         CSR_MCOUNTINHIBIT: mcountinhibit_we = 1'b1;
 
         CSR_MCYCLE,
@@ -1277,6 +1282,15 @@ module ibex_cs_registers import ibex_pkg::*; #(
     end
   end
 
+  always_comb begin : mcounteren_update
+    if (mcounteren_we == 1'b1) begin
+      // bit 1 must always be 0 (no time CSR implemented)
+      mcounteren_d = {csr_wdata_int[MHPMCounterNum+2:2], 1'b0, csr_wdata_int[0]};
+    end else begin
+      mcounteren_d = mcounteren_q;
+    end
+  end
+
   // event selection (hardwired) & control
   always_comb begin : gen_mhpmcounter_incr
 
@@ -1434,6 +1448,25 @@ module ibex_cs_registers import ibex_pkg::*; #(
     end
   end
 
+  if (MHPMCounterNum < 29) begin : g_mcounteren_reduced
+    assign mcounteren = {{29 - MHPMCounterNum{1'b0}}, mcounteren_q};
+  end else begin : g_mcounteren_full
+    assign mcounteren = mcounteren_q;
+  end
+
+  ibex_csr #(
+    .Width     (MHPMCounterNum+3),
+    .ShadowCopy(1'b0),
+    .ResetValue('0)
+  ) u_mcounteren_csr (
+    .clk_i     (clk_i),
+    .rst_ni    (rst_ni),
+    .wr_data_i (mcounteren_d),
+    .wr_en_i   (mcounteren_we),
+    .rd_data_o (mcounteren_q),
+    .rd_error_o()
+  );
+
   /////////////////////////////
   // Debug trigger registers //
   /////////////////////////////