xref: /gem5/src/systemc/tests/systemc/misc/sim_tests/simple_cpu/simple_cpu.cpp

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  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
  implied.  See the License for the specific language governing
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/*****************************************************************************

  simple_cpu.cpp --

  Original Author: Martin Janssen, Synopsys, Inc., 2002-02-15

 *****************************************************************************/

/*****************************************************************************

  MODIFICATION LOG - modifiers, enter your name, affiliation, date and
  changes you are making here.

      Name, Affiliation, Date:
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 *****************************************************************************/

#include "systemc.h"

#define READ 0
#define WRITE 1

SC_MODULE( exec_decode )
{
  SC_HAS_PROCESS( exec_decode );

  sc_in<unsigned>  instruction;
  sc_signal<unsigned>& program_counter;

  unsigned pc; // Program counter
  unsigned cpu_reg[32]; // Cpu registers

  unsigned *data_mem; // The data memory

  exec_decode( sc_module_name NAME,
	       sc_signal<unsigned>& INSTRUCTION,
	       sc_signal<unsigned>& PROGRAM_COUNTER )
    : program_counter(PROGRAM_COUNTER)
  {
    instruction(INSTRUCTION);
	SC_METHOD( entry );
    // sensitive only to the clock
    sensitive << instruction;

    pc = 0x000000; // Power up reset value
    for (int i =0; i<32; i++) cpu_reg[i] = 0;

    // Initialize the data memory from file datamem
    FILE *fp = fopen("simple_cpu/datamem", "r");
    if (fp == (FILE *) 0) return; // No data mem file to read
    // First field in this file is the size of data memory desired
    int size;
    fscanf(fp, "%d", &size);
    data_mem = new unsigned[size];
    if (data_mem == (unsigned *) 0) {
      printf("Not enough memory left\n");
      return;
    }
    unsigned mem_word;
    size = 0;
    while (fscanf(fp, "%x", &mem_word) != EOF) {
      data_mem[size++] = mem_word;
    }

    // Start off simulation by writing program_counter
    program_counter.write(pc);
  }

  // Functionality
  void entry();
};

void
exec_decode::entry()
{
  unsigned instr;
  unsigned opcode;
  unsigned regnum1, regnum2, regnum3;
  unsigned addr;

  int i;

  instr = instruction.read();
  opcode = (instr & 0xe0000000) >> 29; // Extract opcode
  switch(opcode) {
  case 0x0: // Halt
    printf("CPU Halted\n");
    printf("\tPC = 0x%x\n", pc);
    for (i = 0; i < 32; i++)
      printf("\tR[%d] = %x\n", i, cpu_reg[i]);
    // Don't write pc and execution will stop
    break;
  case 0x1: // Store
    regnum1 = (instr & 0x1f000000) >> 24; // Extract register number
    addr = (instr & 0x00ffffff); //  Extract address
    printf("Store: Memory[0x%x] = R[%d]\n", addr, regnum1);
    data_mem[addr] = cpu_reg[regnum1];
    pc = pc + 1;
    program_counter.write(pc);
    break;
  case 0x2: // Load
    regnum1 = (instr & 0x1f000000) >> 24; // Extract register number
    addr = (instr & 0x00ffffff); //  Extract address
    printf("Load: R[%d] = Memory[0x%x]\n", regnum1, addr);
    cpu_reg[regnum1] = data_mem[addr];
    pc = pc + 1;
    program_counter.write(pc);
    break;
  case 0x3: // Add
    regnum1 = (instr & 0x1f000000) >> 24; // Extract register number
    regnum2 = (instr & 0x00f80000) >> 19; // Extract register number
    regnum3 = (instr & 0x0007c000) >> 14; // Extract register number
    printf("R[%d] = R[%d] + R[%d]\n", regnum3, regnum1, regnum2);
    cpu_reg[regnum3] = cpu_reg[regnum1] + cpu_reg[regnum2];
    pc = pc + 1;
    program_counter.write(pc);
    break;
  case 0x4: // Subtract
    regnum1 = (instr & 0x1f000000) >> 24; // Extract register number
    regnum2 = (instr & 0x00f80000) >> 19; // Extract register number
    regnum3 = (instr & 0x0007c000) >> 14; // Extract register number
    printf("R[%d] = R[%d] - R[%d]\n", regnum3, regnum1, regnum2);
    cpu_reg[regnum3] = cpu_reg[regnum1] - cpu_reg[regnum2];
    pc = pc + 1;
    program_counter.write(pc);
    break;
  case 0x5: // Multiply
    regnum1 = (instr & 0x1f000000) >> 24; // Extract register number
    regnum2 = (instr & 0x00f80000) >> 19; // Extract register number
    regnum3 = (instr & 0x0007c000) >> 14; // Extract register number
    printf("R[%d] = R[%d] * R[%d]\n", regnum3, regnum1, regnum2);
    cpu_reg[regnum3] = cpu_reg[regnum1] * cpu_reg[regnum2];
    pc = pc + 1;
    program_counter.write(pc);
    break;
  case 0x6: // Divide
    regnum1 = (instr & 0x1f000000) >> 24; // Extract register number
    regnum2 = (instr & 0x00f80000) >> 19; // Extract register number
    regnum3 = (instr & 0x0007c000) >> 14; // Extract register number
    printf("R[%d] = R[%d] / R[%d]\n", regnum3, regnum1, regnum2);
    if (cpu_reg[regnum2] == 0) {
      printf("Division exception - divide by zero\n");
    }
    else {
      cpu_reg[regnum3] = cpu_reg[regnum1] / cpu_reg[regnum2];
    }
    pc = pc + 1;
    program_counter.write(pc);
    break;
  case 0x7: // JNZ
    regnum1 = (instr & 0x1f000000) >> 24; // Extract register number
    addr = (instr & 0x00ffffff); //  Extract address
    printf("JNZ R[%d] 0x%x\n", regnum1, addr);
    if (cpu_reg[regnum1] == 0x0)
      pc = pc + 1;
    else
      pc = addr;
    program_counter.write(pc);
    break;
  default: // Bad opcode
    printf("Bad opcode 0x%x\n", opcode);
    pc = pc + 1;
    program_counter.write(pc);
    break;
  }
}


SC_MODULE( fetch )
{
  SC_HAS_PROCESS( fetch );

  sc_in<unsigned> program_counter;
  sc_signal<unsigned>& instruction;

  unsigned *prog_mem; // The program memory

  fetch( sc_module_name NAME,
	 sc_signal<unsigned>& PROGRAM_COUNTER,
	 sc_signal<unsigned>& INSTRUCTION )
    : instruction(INSTRUCTION)
  {
    program_counter(PROGRAM_COUNTER);
    SC_METHOD( entry );
    sensitive << program_counter;

    // Initialize the program memory from file progmem
    FILE *fp = fopen("simple_cpu/progmem", "r");
    if (fp == (FILE *) 0) return; // No prog mem file to read
    // First field in this file is the size of program memory desired
    int size;
    fscanf(fp, "%d", &size);
    prog_mem = new unsigned[size];
    if (prog_mem == (unsigned *) 0) {
      printf("Not enough memory left\n");
      return;
    }
    unsigned mem_word;
    size = 0;
    while (fscanf(fp, "%x", &mem_word) != EOF) {
      prog_mem[size++] = mem_word;
    }
    instruction.write(0);
  }

  // Functionality
  void entry();
};

void fetch::entry()
{
  unsigned pc, instr;
  pc = program_counter.read();
  instr = prog_mem[pc];
  instruction.write(instr);
}

int
sc_main(int ac, char *av[])
{
  sc_signal<unsigned> pc;
  sc_signal<unsigned> instr;

  exec_decode ED("ED", instr, pc);
  fetch F("F", pc, instr);

  // instead of a testbench routine, we include the testbench here
  sc_start(1, SC_NS);
  sc_start( 10, SC_NS );

  fflush( stdout );

  return 0;
}