diff --git a/inc/CPU.h b/inc/CPU.h
index d95cb9f..5843109 100644
--- a/inc/CPU.h
+++ b/inc/CPU.h
@@ -15,10 +15,11 @@
 #include "tlm_utils/simple_initiator_socket.h"
 
 #include "memory.h"
-#include "Instruction.h"
 #include "Execute.h"
 #include "Registers.h"
 #include "Log.h"
+#include "Instruction.h"
+#include "C_Instruction.h"
 
 using namespace sc_core;
 using namespace sc_dt;
@@ -52,10 +53,11 @@ private:
    * @param  inst instruction to execute
    * @return  true if PC is affected by instruction
    */
-  bool process_default_instruction(Instruction &inst);
+  bool process_base_instruction(Instruction &inst);
+
+  bool process_c_instruction(Instruction &inst);
 
 
-  
   void CPU_thread(void);
 };
 
diff --git a/inc/Execute.h b/inc/Execute.h
index bf2a7a2..53de892 100644
--- a/inc/Execute.h
+++ b/inc/Execute.h
@@ -16,6 +16,7 @@
 
 #include "memory.h"
 #include "Instruction.h"
+#include "C_Instruction.h"
 #include "Registers.h"
 #include "Log.h"
 
@@ -43,7 +44,7 @@ public:
   void LUI(Instruction &inst);
   void AUIPC(Instruction &inst);
 
-  void JAL(Instruction &inst);
+  void JAL(Instruction &inst, bool c_extension = false, int m_rd = 1);
   void JALR(Instruction &inst);
 
   void BEQ(Instruction &inst);
@@ -55,7 +56,7 @@ public:
 
   void LB(Instruction &inst);
   void LH(Instruction &inst);
-  void LW(Instruction &inst);
+  void LW(Instruction &inst, bool c_extension = false);
   void LBU(Instruction &inst);
   void LHU(Instruction &inst);
 
@@ -65,7 +66,7 @@ public:
   void SBU(Instruction &inst);
   void SHU(Instruction &inst);
 
-  void ADDI(Instruction &inst);
+  void ADDI(Instruction &inst, bool c_extension = false);
   void SLTI(Instruction &inst);
   void SLTIU(Instruction &inst);
   void XORI(Instruction &inst);
@@ -87,6 +88,9 @@ public:
   void OR(Instruction &inst);
   void AND(Instruction &inst);
 
+  void FENCE(Instruction &inst);
+  void ECALL(Instruction &inst);
+
   void CSRRW(Instruction &inst);
   void CSRRS(Instruction &inst);
   void CSRRC(Instruction &inst);
@@ -94,6 +98,19 @@ public:
   void CSRRSI(Instruction &inst);
   void CSRRCI(Instruction &inst);
 
+  void MRET(Instruction &inst);
+
+  /* C Extensions */
+  void C_JR(Instruction &inst);
+  void C_MV(Instruction &inst);
+  void C_LWSP(Instruction &inst);
+  void C_ADDI4SPN(Instruction &inst);
+  void C_ADDI16SP(Instruction &inst);
+  void C_SWSP(Instruction &inst);
+  void C_BEQZ(Instruction &inst);
+  void C_BNEZ(Instruction &inst);
+  void C_LI(Instruction &inst);
+
   void NOP(Instruction &inst);
 
 private:
diff --git a/inc/Instruction.h b/inc/Instruction.h
index 9c22365..897b52e 100644
--- a/inc/Instruction.h
+++ b/inc/Instruction.h
@@ -14,6 +14,23 @@ using namespace sc_core;
 using namespace sc_dt;
 using namespace std;
 
+typedef enum {
+  BASE_EXTENSION,
+  M_EXTENSION,
+  A_EXTENSION,
+  F_EXTENSION,
+  D_EXTENSION,
+  Q_EXTENSION,
+  L_EXTENSION,
+  C_EXTENSION,
+  R_EXTENSION,
+  J_EXTENSION,
+  P_EXTENSION,
+  V_EXTENSION,
+  N_EXTENSION,
+  UNKNOWN_EXTENSION
+} extension_t;
+
 typedef enum {
 OP_LUI,
 OP_AUIPC,
@@ -58,6 +75,21 @@ OP_SRA,
 OP_OR,
 OP_AND,
 
+OP_FENCE,
+OP_ECALL,
+OP_EBREAK,
+
+OP_CSRRW,
+OP_CSRRS,
+OP_CSRRC,
+OP_CSRRWI,
+OP_CSRRSI,
+OP_CSRRCI,
+
+OP_URET,
+OP_SRET,
+OP_MRET,
+
 OP_ERROR
 } opCodes;
 
@@ -116,6 +148,21 @@ typedef enum {
   SRA_F7  = 0b0100000,
   OR_F    = 0b110,
   AND_F   = 0b111,
+
+  FENCE   = 0b0001111,
+  ECALL   = 0b1110011,
+  ECALL_F = 0b000000000000,
+  EBREAK_F= 0b000000000001,
+  URET_F  = 0b000000000010,
+  SRET_F  = 0b000100000010,
+  MRET_F  = 0b001100000010,
+  ECALL_F3= 0b000,
+  CSRRW   = 0b001,
+  CSRRS   = 0b010,
+  CSRRC   = 0b011,
+  CSRRWI  = 0b101,
+  CSRRSI  = 0b110,
+  CSRRCI  = 0b111,
 } Codes;
 
 /**
@@ -311,7 +358,11 @@ public:
   }
 
   inline int32_t get_csr() {
-    return get_imm_I();
+    int32_t aux = 0;
+
+    aux = m_instr.range(31, 20);
+
+    return aux;
   }
 
   /**
@@ -320,6 +371,18 @@ public:
    */
   opCodes decode();
 
+  /**
+   * @brief returns what instruction extension
+   * @return extension
+   */
+  extension_t check_extension();
+
+
+  uint32_t getInstr() {
+    return m_instr;
+  }
+
+
   inline void dump() {
     cout << hex << "0x" << m_instr << dec << endl;
   }
diff --git a/inc/Memory.h b/inc/Memory.h
index 7245a61..9f9f5b9 100644
--- a/inc/Memory.h
+++ b/inc/Memory.h
@@ -48,14 +48,12 @@ public:
   // *********************************************
   // TLM-2 forward DMI method
   // *********************************************
-
   virtual bool get_direct_mem_ptr(tlm::tlm_generic_payload& trans,
                                   tlm::tlm_dmi& dmi_data);
 
   // *********************************************
   // TLM-2 debug transport method
   // *********************************************
-
   virtual unsigned int transport_dbg(tlm::tlm_generic_payload& trans);
 
 private:
diff --git a/src/CPU.cpp b/src/CPU.cpp
index 9b9192e..7cd2dc2 100644
--- a/src/CPU.cpp
+++ b/src/CPU.cpp
@@ -1,4 +1,3 @@
-
 #include "CPU.h"
 
 SC_HAS_PROCESS(CPU);
@@ -22,7 +21,69 @@ CPU::~CPU() {
   cout << "*********************************************" << endl;
 }
 
-bool CPU::process_default_instruction(Instruction &inst) {
+bool CPU::process_c_instruction(Instruction &inst) {
+  bool PC_not_affected = true;
+
+  C_Instruction c_inst(inst.getInstr());
+
+  switch(c_inst.decode()) {
+    case OP_C_ADDI4SPN:
+      exec->C_ADDI4SPN(inst);
+      break;
+    case OP_C_LW:
+      exec->LW(inst, true);
+      break;
+    case OP_C_ADDI:
+      exec->ADDI(inst, true);
+      break;
+    case OP_C_JAL:
+      exec->JAL(inst, true, 1);
+      PC_not_affected = false;
+      break;
+    case OP_C_J:
+      exec->JAL(inst, true, 0);
+      PC_not_affected = false;
+      break;
+    case OP_C_LI:
+      exec->C_LI(inst);
+      break;
+    case OP_C_LWSP:
+      exec->C_LWSP(inst);
+      break;
+    case OP_C_JR:
+      exec->C_JR(inst);
+      PC_not_affected = false;
+      break;
+    case OP_C_MV:
+      exec->C_MV(inst);
+      break;
+    case OP_C_SWSP:
+      exec->C_SWSP(inst);
+      break;
+    case OP_C_ADDI16SP:
+      exec->C_ADDI16SP(inst);
+      break;
+    case OP_C_BEQZ:
+      exec->C_BEQZ(inst);
+      PC_not_affected = false;
+      break;
+    case OP_C_BNEZ:
+      exec->C_BNEZ(inst);
+      PC_not_affected = false;
+      break;
+    default:
+      std::cout << "C instruction not implemented yet" << endl;
+      inst.dump();
+      exec->NOP(inst);
+      //sc_stop();
+      break;
+
+  }
+
+  return PC_not_affected;
+}
+
+bool CPU::process_base_instruction(Instruction &inst) {
   bool PC_not_affected = true;
 
   switch(inst.decode()) {
@@ -156,7 +217,40 @@ bool CPU::process_default_instruction(Instruction &inst) {
       exec->CSRRC(inst);
       break;
 #endif
+    case OP_FENCE:
+      exec->FENCE(inst);
+      break;
+    case OP_ECALL:
+      exec->ECALL(inst);
+      break;
+    case OP_CSRRW:
+      exec->CSRRW(inst);
+      break;
+    case OP_CSRRS:
+      exec->CSRRS(inst);
+      break;
+    case OP_CSRRC:
+      exec->CSRRC(inst);
+      break;
+    case OP_CSRRWI:
+      exec->CSRRWI(inst);
+      break;
+    case OP_CSRRSI:
+      exec->CSRRSI(inst);
+      break;
+    case OP_CSRRCI:
+      exec->CSRRCI(inst);
+      break;
+
+    case OP_MRET:
+      exec->MRET(inst);
+      PC_not_affected = false;
+      break;
     default:
+      std::cout << "Wrong instruction" << endl;
+      inst.dump();
+      exec->NOP(inst);
+      //sc_stop();
       break;
   }
 
@@ -173,6 +267,7 @@ void CPU::CPU_thread(void) {
   uint32_t INSTR;
   sc_time delay = SC_ZERO_TIME;
   bool PC_not_affected;
+  bool incPCby2 = false;
 
   trans->set_command( tlm::TLM_READ_COMMAND );
   trans->set_data_ptr( reinterpret_cast<unsigned char*>(&INSTR) );
@@ -197,14 +292,26 @@ void CPU::CPU_thread(void) {
         log->SC_log(Log::INFO) << "PC: " << hex << register_bank->getPC()
               << dec << endl;
 
-
         Instruction inst(INSTR);
 
         /* check what type of instruction is and execute it */
+        switch(inst.check_extension()) {
+          case BASE_EXTENSION:
+            PC_not_affected = process_base_instruction(inst);
+            incPCby2 = false;
+            break;
+          case C_EXTENSION:
+            PC_not_affected = process_c_instruction(inst);
+            incPCby2 = true;
+            break;
+          default:
+            std::cout << "Extension not implemented yet" << std::endl;
+            inst.dump();
+            exec->NOP(inst);
+        }
 
 
 
-        PC_not_affected = process_default_instruction(inst);
 
 
           // default:
@@ -215,7 +322,7 @@ void CPU::CPU_thread(void) {
         perf->instructionsInc();
 
         if (PC_not_affected == true) {
-          register_bank->incPC();
+          register_bank->incPC(incPCby2);
         }
   } // while(1)
 } // CPU_thread
diff --git a/src/Execute.cpp b/src/Execute.cpp
index a949e2c..4b6f8db 100644
--- a/src/Execute.cpp
+++ b/src/Execute.cpp
@@ -30,28 +30,39 @@ void Execute::AUIPC(Instruction &inst) {
   imm = inst.get_imm_U() << 12;
   new_pc = regs->getPC() + imm;
 
-  regs->setPC(new_pc);
   regs->setValue(rd, new_pc);
 
   log->SC_log(Log::INFO) << "AUIPC x" << rd << " + PC -> PC (" << new_pc << ")" << endl;
 }
 
-void Execute::JAL(Instruction &inst) {
+void Execute::JAL(Instruction &inst, bool c_extension, int m_rd) {
   int32_t mem_addr = 0;
   int rd;
   int new_pc, old_pc;
 
-  rd = inst.get_rd();
-  mem_addr = inst.get_imm_J();
+  if (c_extension == false) {
+    rd = inst.get_rd();
+    mem_addr = inst.get_imm_J();
+    old_pc = regs->getPC();
+    new_pc = old_pc + mem_addr;
 
-  old_pc = regs->getPC();
+    regs->setPC(new_pc);
 
+    old_pc = old_pc + 4;
+    regs->setValue(rd, old_pc);
+  } else {
+    C_Instruction c_inst(inst.getInstr());
 
-  new_pc = old_pc + mem_addr;
-  regs->setPC(new_pc);
+    rd = m_rd;
+    mem_addr = c_inst.get_imm_J();
+    old_pc = regs->getPC();
 
-  old_pc = old_pc + 4;
-  regs->setValue(rd, old_pc);
+    new_pc = old_pc + mem_addr;
+    regs->setPC(new_pc);
+
+    old_pc = old_pc + 2;
+    regs->setValue(rd, old_pc);
+  }
 
   log->SC_log(Log::INFO) << dec << "JAL: x" << rd << " <- 0x" << hex << old_pc
           << dec << " PC + " << mem_addr << " -> PC (0x"
@@ -226,21 +237,29 @@ void Execute::LH(Instruction &inst) {
           << hex <<mem_addr << dec << ") -> x" << rd << endl;
 }
 
-void Execute::LW(Instruction &inst) {
+void Execute::LW(Instruction &inst, bool c_extension) {
   uint32_t mem_addr = 0;
   int rd, rs1;
   int32_t imm = 0;
   uint32_t data;
 
-  rd = inst.get_rd();
-  rs1 = inst.get_rs1();
-  imm = inst.get_imm_I();
+  if (c_extension == false) {
+    rd = inst.get_rd();
+    rs1 = inst.get_rs1();
+    imm = inst.get_imm_I();
+  } else {
+    C_Instruction c_inst(inst.getInstr());
+
+    rd = c_inst.get_rdp();
+    rs1 = c_inst.get_rs1p();
+    imm = c_inst.get_imm_L();
+  }
 
   mem_addr = imm + regs->getValue(rs1);
   data = readDataMem(mem_addr, 4);
   regs->setValue(rd, data);
 
-  log->SC_log(Log::INFO) << "LW: x" << rs1 << " + " << imm << " (@0x"
+  log->SC_log(Log::INFO) << "C.LW: x" << rs1 << " + " << imm << " (@0x"
           << hex <<mem_addr << dec << ") -> x" << rd << endl;
 }
 
@@ -338,14 +357,22 @@ void Execute::SW(Instruction &inst) {
           << " (@0x" << hex << mem_addr << dec << ")" <<  endl;
 }
 
-void Execute::ADDI(Instruction &inst) {
+void Execute::ADDI(Instruction &inst, bool c_extension) {
   int rd, rs1;
   int32_t imm = 0;
   int32_t calc;
 
-  rd = inst.get_rd();
-  rs1 = inst.get_rs1();
-  imm = inst.get_imm_I();
+  if (c_extension == false) {
+    rd = inst.get_rd();
+    rs1 = inst.get_rs1();
+    imm = inst.get_imm_I();
+  } else {
+    C_Instruction c_inst(inst.getInstr());
+
+    rd = c_inst.get_rd();
+    rs1 = rd;
+    imm = c_inst.get_imm_I();
+  }
 
   calc = regs->getValue(rs1) + imm;
   regs->setValue(rd, calc);
@@ -658,6 +685,20 @@ void Execute::AND(Instruction &inst) {
           << "-> x" << rd << endl;
 }
 
+void Execute::FENCE(Instruction &inst) {
+  log->SC_log(Log::INFO) << "FENCE" << endl;
+}
+
+void Execute::ECALL(Instruction &inst) {
+
+  log->SC_log(Log::INFO) << "ECALL" << endl;
+  std::cout << "ECALL Instruction called, stopping simulation" << endl;
+  regs->dump();
+  cout << "Simulation time " << sc_time_stamp() << endl;
+  perf->dump();
+
+  SC_REPORT_ERROR("Execute", "ECALL");
+}
 void Execute::CSRRW(Instruction &inst) {
   int rd, rs1;
   int csr;
@@ -667,13 +708,11 @@ void Execute::CSRRW(Instruction &inst) {
   rs1 = inst.get_rs1();
   csr = inst.get_csr();
 
-  if (rd == 0) {
-    return;
-  }
-
   /* These operations must be atomical */
-  aux = regs->getCSR(csr);
-  regs->setValue(rd, aux);
+  if (rd != 0) {
+    aux = regs->getCSR(csr);
+    regs->setValue(rd, aux);
+  }
   aux = regs->getValue(rs1);
   regs->setCSR(csr, aux);
 
@@ -731,6 +770,267 @@ void Execute::CSRRC(Instruction &inst) {
           << ". x" << rs1 << " & CSR #" << csr << endl;
 }
 
+void Execute::CSRRWI(Instruction &inst) {
+  int rd, rs1;
+  int csr;
+  uint32_t aux;
+
+  rd = inst.get_rd();
+  rs1 = inst.get_rs1();
+  csr = inst.get_csr();
+
+
+  /* These operations must be atomical */
+  if (rd != 0) {
+    aux = regs->getCSR(csr);
+    regs->setValue(rd, aux);
+  }
+  aux = rs1;
+  regs->setCSR(csr, aux);
+
+  log->SC_log(Log::INFO) << "CSRRWI: CSR #" << csr << " -> x" << rd
+          << ". x" << rs1 << "-> CSR #" << csr << endl;
+}
+
+void Execute::CSRRSI(Instruction &inst) {
+  int rd, rs1;
+  int csr;
+  uint32_t bitmask, aux;
+
+  rd = inst.get_rd();
+  rs1 = inst.get_rs1();
+  csr = inst.get_csr();
+
+  if (rs1 == 0) {
+    return;
+  }
+
+  /* These operations must be atomical */
+  aux = regs->getCSR(csr);
+  regs->setValue(rd, aux);
+
+  bitmask = rs1;
+  aux = aux | bitmask;
+  regs->setCSR(csr, aux);
+
+  log->SC_log(Log::INFO) << "CSRRSI: CSR #" << csr << " -> x" << rd
+          << ". x" << rs1 << " & CSR #" << csr << endl;
+}
+
+void Execute::CSRRCI(Instruction &inst) {
+  int rd, rs1;
+  int csr;
+  uint32_t bitmask, aux;
+
+  rd = inst.get_rd();
+  rs1 = inst.get_rs1();
+  csr = inst.get_csr();
+
+  if (rs1 == 0) {
+    return;
+  }
+
+  /* These operations must be atomical */
+  aux = regs->getCSR(csr);
+  regs->setValue(rd, aux);
+
+  bitmask = rs1;
+  aux = aux & ~bitmask;
+  regs->setCSR(csr, aux);
+
+  log->SC_log(Log::INFO) << "CSRRCI: CSR #" << csr << " -> x" << rd
+          << ". x" << rs1 << " & CSR #" << csr << endl;
+}
+
+void Execute::MRET(Instruction &inst) {
+  uint32_t new_pc = 0;
+
+  new_pc = regs->getCSR(0x341);
+  regs->setPC(new_pc);
+
+  log->SC_log(Log::INFO) << "MRET: PC <- 0x" << hex << new_pc << endl;
+}
+
+void Execute::C_JR(Instruction &inst) {
+  uint32_t mem_addr = 0;
+  int rd, rs1;
+  int new_pc, old_pc;
+
+  C_Instruction c_inst(inst.getInstr());
+
+  rd = 0;
+  rs1 = c_inst.get_rs1();
+  mem_addr = 0;
+
+  std::cout << "rs1 :" << rs1 << std::endl;
+  old_pc = regs->getPC();
+  regs->setValue(rd, old_pc + 4);
+
+
+  new_pc = (regs->getValue(rs1) + mem_addr) & 0xFFFFFFFE;
+  regs->setPC(new_pc);
+
+  log->SC_log(Log::INFO) << "JR: x" << dec << rd << " <- 0x" << hex << old_pc + 4
+          << " PC <- 0x" << hex << new_pc << endl;
+}
+
+void Execute::C_MV(Instruction &inst) {
+  int rd, rs1, rs2;
+  uint32_t calc;
+
+  C_Instruction c_inst(inst.getInstr());
+
+  rd = c_inst.get_rd();
+  rs1 = 0;
+  rs2 = c_inst.get_rs2();
+
+  calc = regs->getValue(rs1) + regs->getValue(rs2);
+  regs->setValue(rd, calc);
+
+  log->SC_log(Log::INFO) << "MV: x" << rs1 << " + x" << rs2 << " -> x" << rd << endl;
+}
+
+void Execute::C_LWSP(Instruction &inst) {
+  uint32_t mem_addr = 0;
+  int rd, rs1;
+  int32_t imm = 0;
+  uint32_t data;
+
+  C_Instruction c_inst(inst.getInstr());
+
+  rd = c_inst.get_rd();
+  rs1 = c_inst.get_rs1();
+  imm = c_inst.get_imm_LWSP();
+
+  mem_addr = imm + regs->getValue(rs1);
+  data = readDataMem(mem_addr, 4);
+  regs->setValue(rd, data);
+
+  log->SC_log(Log::INFO) << "C.LWSP: x" << rs1 << " + " << imm << " (@0x"
+          << hex <<mem_addr << dec << ") -> x" << rd << endl;
+}
+
+void Execute::C_ADDI4SPN(Instruction  &inst) {
+  int rd, rs1;
+  int32_t imm = 0;
+  int32_t calc;
+
+  C_Instruction c_inst(inst.getInstr());
+
+  rd = c_inst.get_rdp();
+  rs1 = 2;
+  imm = c_inst.get_imm_ADDI4SPN();
+
+  calc = regs->getValue(rs1) + imm;
+  regs->setValue(rd, calc);
+
+  log->SC_log(Log::INFO) << dec << "ADDI4SPN: x" << rs1 << " + " << imm << " -> x" << rd << endl;
+}
+
+void Execute::C_ADDI16SP(Instruction &inst) {
+  // addi x2, x2, nzimm[9:4]
+  int rd, rs1;
+  int32_t imm = 0;
+  int32_t calc;
+
+  C_Instruction c_inst(inst.getInstr());
+
+  rd = 2;
+  rs1 = 2;
+  imm = c_inst.get_imm_ADDI16SP();
+
+
+  calc = regs->getValue(rs1) + imm;
+  regs->setValue(rd, calc);
+
+  log->SC_log(Log::INFO) << dec << "ADDI16SP: x" << rs1 << " + " << imm << " -> x" << rd << endl;
+}
+
+void Execute::C_SWSP(Instruction &inst) {
+  // sw rs2, offset(x2)
+  uint32_t mem_addr = 0;
+  int rs1, rs2;
+  int32_t imm = 0;
+  uint32_t data;
+
+  C_Instruction c_inst(inst.getInstr());
+
+  rs1 = 2;
+  rs2 = 2;
+  imm = c_inst.get_imm_CSS();
+
+  mem_addr = imm + regs->getValue(rs1);
+  data = regs->getValue(rs2);
+
+  writeDataMem(mem_addr, data, 4);
+
+  log->SC_log(Log::INFO) << "SWSP: x" << dec << rs2 << "(0x" << hex << data
+          << ") -> x" << dec << rs1 << " + " << imm
+          << " (@0x" << hex << mem_addr << dec << ")" <<  endl;
+
+}
+
+void Execute::C_BEQZ(Instruction &inst) {
+  int rs1;
+  int new_pc = 0;
+  uint32_t val1;
+  C_Instruction c_inst(inst.getInstr());
+
+  rs1 = c_inst.get_rs1p();
+  val1 = regs->getValue(rs1);
+
+  if (val1 == 0) {
+    new_pc = regs->getPC() + c_inst.get_imm_CB();
+    regs->setPC(new_pc);
+  } else {
+    regs->incPC(true); //PC <- PC +2
+  }
+
+  log->SC_log(Log::INFO) << "C.BEQZ: x" << rs1 << "(" <<  val1
+          << ") == 0? -> PC (" << new_pc << ")" << endl;
+}
+
+void Execute::C_BNEZ(Instruction &inst) {
+  int rs1;
+  int new_pc = 0;
+  uint32_t val1;
+  C_Instruction c_inst(inst.getInstr());
+
+  rs1 = c_inst.get_rs1p();
+  val1 = regs->getValue(rs1);
+
+  if (val1 != 0) {
+    new_pc = regs->getPC() + c_inst.get_imm_CB();
+    regs->setPC(new_pc);
+  } else {
+    regs->incPC(true); //PC <- PC +2
+  }
+
+  log->SC_log(Log::INFO) << "C.BNEZ: x" << rs1 << "(" <<  val1
+          << ") == 0? -> PC (" << new_pc << ")" << endl;
+}
+
+void Execute::C_LI(Instruction &inst) {
+
+  int rd, rs1;
+  int32_t imm = 0;
+  int32_t calc;
+
+  C_Instruction c_inst(inst.getInstr());
+
+  rd = c_inst.get_rd();
+  rs1 = 0;
+  imm = c_inst.get_imm_ADDI();
+
+  calc = regs->getValue(rs1) + imm;
+  regs->setValue(rd, calc);
+
+  log->SC_log(Log::INFO) << dec << "LI: x" << rs1 << " + " << imm << " -> x" << rd << endl;
+
+}
+
+
+
 void Execute::NOP(Instruction &inst) {
   cout << endl;
   regs->dump();
diff --git a/src/Instruction.cpp b/src/Instruction.cpp
index e19e130..503eec8 100644
--- a/src/Instruction.cpp
+++ b/src/Instruction.cpp
@@ -112,8 +112,64 @@ opCodes Instruction::decode() {
           return OP_AND;
       }
     } /* ADD */
-      return OP_ERROR;
+    case FENCE:
+      return OP_FENCE;
+    case ECALL: {
+      switch (get_funct3()) {
+        case ECALL_F3:
+          switch(get_csr()) {
+            case ECALL_F:
+              return OP_ECALL;
+            case EBREAK_F:
+                return OP_EBREAK;
+            case URET_F:
+              return OP_URET;
+            case SRET_F:
+              return OP_SRET;
+            case MRET_F:
+              return OP_MRET;
+          }
+          break;
+        case CSRRW:
+          return OP_CSRRW;
+          break;
+        case CSRRS:
+          return OP_CSRRS;
+          break;
+        case CSRRC:
+          return OP_CSRRC;
+          break;
+        case CSRRWI:
+          return OP_CSRRWI;
+          break;
+        case CSRRSI:
+          return OP_CSRRSI;
+          break;
+        case CSRRCI:
+          return OP_CSRRCI;
+          break;
+      }
+    }
     default:
       return OP_ERROR;
   }
 }
+
+
+extension_t Instruction::check_extension() {
+  if (m_instr.range(1,0) == 0b11) {
+    return BASE_EXTENSION;
+  } else if (m_instr.range(1,0) == 0b00) {
+    return C_EXTENSION;
+  } else if (m_instr.range(1,0) == 0b01) {
+    return C_EXTENSION;
+  } else if (m_instr.range(1,0) == 0b10) {
+    return C_EXTENSION;
+  } else if (m_instr.range(6,0) == 0b0110011) {
+    return M_EXTENSION;
+  } else if (m_instr.range(6,0) == 0b0101111) {
+    return A_EXTENSION;
+  } else {
+    return UNKNOWN_EXTENSION;
+  }
+}
diff --git a/src/Registers.cpp b/src/Registers.cpp
index caceb43..94391f5 100644
--- a/src/Registers.cpp
+++ b/src/Registers.cpp
@@ -2,7 +2,8 @@
 
 Registers::Registers() {
 
-  memset(register_bank, 0, sizeof(int32_t)*32); // 32 registers of 32 bits each
+  memset(register_bank, 0, sizeof(uint32_t)*32); // 32 registers of 32 bits each
+  memset(CSR, 0, sizeof(uint32_t)*4096);
   perf = Performance::getInstance();
 
   register_bank[sp] = 1024-1;  // SP points to end of memory