diff --git a/src/cpu/csr.c b/src/cpu/csr.c
new file mode 100644
index 0000000..bcd159c
--- /dev/null
+++ b/src/cpu/csr.c
@@ -0,0 +1,21 @@
+#include "csr.h"
+#include "rv32cpu.h"
+
+uint32_t csr_read(struct RV32_CPU* cpu, uint32_t csr)
+{
+    switch(csr)
+    {
+        case CSR_TIME:
+            return cpu->sim_ticks_done;
+            break;
+        default:
+            break;
+    }
+
+    return cpu->csr[csr];
+}
+
+void csr_write(struct RV32_CPU* cpu, uint32_t csr, uint32_t value)
+{
+    cpu->csr[csr] = value;
+}
diff --git a/src/cpu/csr.h b/src/cpu/csr.h
index f7d4796..317398d 100644
--- a/src/cpu/csr.h
+++ b/src/cpu/csr.h
@@ -1,9 +1,17 @@
 #ifndef CSR_H
 #define CSR_H
 
+#include <stdint.h>
+
 /* ZICSR : Control and Status Registers */
 #define CSR_COUNT 0x2000
 
+/* Unprivileged CSR */
+#define CSR_CYCLE 0xC00
+#define CSR_TIME 0xC01
+#define CSR_CYCLEH 0xC80
+#define CSR_TIMEH 0xC81
+
 /* Supervisor-level CSR */
 /* Supervisor Trap setup CSR */
 #define CSR_SSTATUS 0x100
diff --git a/src/cpu/rv32cpu.c b/src/cpu/rv32cpu.c
index bea9c9c..744df55 100644
--- a/src/cpu/rv32cpu.c
+++ b/src/cpu/rv32cpu.c
@@ -507,6 +507,7 @@ static void cpu_execute(rv32_cpu_t* cpu, instruction_t* instruction)
 		}
 		case OPCODE_SYSTEM:
 		{
+			uint32_t csr = instruction->immediate;
 			switch(instruction->func3)
 			{
 				case FUNC3_ECALL_EBREAK:
@@ -549,35 +550,39 @@ static void cpu_execute(rv32_cpu_t* cpu, instruction_t* instruction)
 					break;
 				case FUNC3_CSRRW:
 					// CSR atomic Read/Write
-					uint32_t csrrw_old_value = cpu->csr[instruction->immediate];
-					cpu->csr[instruction->immediate] = cpu->regs.x[instruction->rs1];
+					uint32_t csrrw_old_value = 0;
+					if(instruction->rd)
+						csrrw_old_value = csr_read(cpu, csr);
+					csr_write(cpu, csr, cpu->regs.x[instruction->rs1]);
 					cpu->regs.x[instruction->rd] = csrrw_old_value;
 					break;
 				case FUNC3_CSRRS:
 					// CSR atomic Read and Set bits
-					cpu->regs.x[instruction->rd] = cpu->csr[instruction->immediate];
-					cpu->csr[instruction->immediate] |= cpu->regs.x[instruction->rs1];
+					cpu->regs.x[instruction->rd] = csr_read(cpu, csr);
+					csr_write(cpu, csr, cpu->regs.x[instruction->rd] | cpu->regs.x[instruction->rs1]);
 					break;
 				case FUNC3_CSRRC:
 					// CSR atomic Read and Clear bits
-					cpu->regs.x[instruction->rd] = cpu->csr[instruction->immediate];
-					cpu->csr[instruction->immediate] &= (~cpu->regs.x[instruction->rs1]);
+					cpu->regs.x[instruction->rd] = csr_read(cpu, csr);
+					csr_write(cpu, csr, cpu->regs.x[instruction->rd] & (~cpu->regs.x[instruction->rs1]));
 					break;
 				case FUNC3_CSRRWI:
 					// CSR atomic Read/Write Immediate (immediate in rs1)
-					uint32_t csrrwi_old_value = cpu->csr[instruction->immediate];
-					cpu->csr[instruction->immediate] = instruction->rs1;
+					uint32_t csrrwi_old_value = 0;
+					if(instruction->rd)
+						csrrwi_old_value = csr_read(cpu, csr);
+					csr_write(cpu, csr, instruction->rs1);
 					cpu->regs.x[instruction->rd] = csrrwi_old_value;
 					break;
 				case FUNC3_CSRRSI:
 					// CSR atomic Read and Set bits immediate
-					cpu->regs.x[instruction->rd] = cpu->csr[instruction->immediate];
-					cpu->csr[instruction->immediate] |= instruction->rs1;
+					cpu->regs.x[instruction->rd] = csr_read(cpu, csr);
+					csr_write(cpu, csr, cpu->regs.x[instruction->rd] | instruction->rs1);
 					break;
 				case FUNC3_CSRRCI:
 					// CSR atomic Read and Clear bits Immediate (immediate in rs1)
-					cpu->regs.x[instruction->rd] = cpu->csr[instruction->immediate];
-					cpu->csr[instruction->immediate] &= (~((uint32_t) instruction->rs1));
+					cpu->regs.x[instruction->rd] = csr_read(cpu, csr);
+					csr_write(cpu, csr, cpu->regs.x[instruction->rd] & (~((uint32_t) instruction->rs1)));
 					break;
 				default:
 					fprintf(stderr, "FATAL: Unknown func3 0x%x for SYSTEM instruction while executing\n", instruction->func3);
diff --git a/src/cpu/rv32cpu.h b/src/cpu/rv32cpu.h
index f6248ed..e931784 100644
--- a/src/cpu/rv32cpu.h
+++ b/src/cpu/rv32cpu.h
@@ -207,6 +207,9 @@ typedef struct RV32_CPU
 	pthread_cond_t sim_condition;
 } rv32_cpu_t;
 
+uint32_t csr_read(struct RV32_CPU* cpu, uint32_t csr);
+void csr_write(struct RV32_CPU* cpu, uint32_t csr, uint32_t value);
+
 extern rv32_cpu_t* cpu0;
 extern pthread_mutex_t cpu0_mutex;
 void cpu_init();