// Test Arduino (328p) power reduction for power consumption

// mode 0 - Do nothing - leave everything on (although uninitialised)
// mode 1 - switch off the Analogue to Digital Converter (ADC)
// Mode 2 - Switch off the serial UART
// Mode 3 - Switch off Serial Peripheral Interface (SPI)
// Mode 4 - Switch off Timer/counter 1
// Mode 5 - Switch off Timer/counter 0 (which affects delay(), millis() etc)
// Mode 6 - Switch off Timer/counter 2
// Mode 7 - Switch off Two Wire Interface (TWI)
// Mode 8 - Switch off ADC, SPI, TC1, TC2, TWI
// Mode 9 - Switch everything off!

// Results:
// 0 = 39.5 41.0
// 1 = 39.4 40.0
// 2 = 40.1 40.0
// 3 = 39.1 39.9
// 4 = 40.3 40.8
// 5 = 38.3 38.5
// 6 = 39.1 39.4
// 7 = 38.9 39.1
// 8 = 35.9 36.0
// 9 = 33.7 33.6

int test_mode = 8;

// Using this variable works around a bug in some systems
// See: http://arduino.cc/forum/index.php/topic,59965.msg432768.html
int delay_time = 10000;

void setup() {
  // Power reduction register
  // Bit 7 = Two Wire Interface (TWI)
  // Bit 6 = Timer/counter 2
  // Bit 5 = Timer/counter 0
  // Bit 4 = reserved
  // Bit 3 = Timer/counter 1
  // Bit 2 = Serial peripheral interface (SPI)
  // Bit 1 = USART0
  // Bit 0 = ADC
  switch(test_mode) {
    case 0:
      PRR = 0x00;
      break;
    case 1:
      PRR = 0x01;
      break;
    case 2:
      PRR = 0x02;
      break;
    case 3:
      PRR = 0x04;
      break;
    case 4:
      PRR = 0x10;
      break;
    case 5:
      PRR = 0x20;
      break;
    case 6:
      PRR = 0x40;
      break;
    case 7:
      PRR = 0x80;
      break;
    case 8:
      PRR = 0xCD;
      break;
    case 9:
      PRR = 0xEF;
      break;
  }
}

// This is supposed to be a constant 'load'. Looping continuously may
// cause variable current consumption, so I'm hoping a long delay will
// mean the chip is in a 'constant' state.
void loop() {
  delay(delay_time);
}