Arduino & the ISD4002

I've been taking an engineering class this semester that focuses on designing electronics that produce music. We're all using the Arduino microcontroller platform, and one of our tasks is to get the ISD4002 chip (a sound recorder) communicating with the Arduino through SPI. I haven't been able to find any evidence of the ISD4002 chip working with the Arduino on Google, so hopefully this code will be useful to someone.

The following program first initializes SPI, Serial, and the ISD chip. The flow of the main loop is:
Record for 10 sec --> Pause 2 sec --> Play for 10 sec --> Pause for 2 sec.

#define DATAOUT     11  // MOSI
#define DATAIN      12  // MISO
#define SPICLOCK    13  // SCK
#define SLAVESELECT 10  // SS

#define ISD_OPCODE_POWERUP   B00100
#define ISD_OPCODE_SETPLAY   B00111
#define ISD_OPCODE_PLAY      B01111
#define ISD_OPCODE_SETREC    B00101
#define ISD_OPCODE_REC       B01101
#define ISD_OPCODE_STOP      B01100
#define ISD_OPCODE_POWERDOWN B00000
#define ISD_POWERUP_DELAY    25

char spi_transfer(volatile char data) {
  SPDR = data;
  while (!(SPSR & (1<<SPIF))) { }
  return SPDR;
}

void spi_init() {
  byte clr;
  pinMode(DATAOUT, OUTPUT);
  pinMode(DATAIN, INPUT);
  pinMode(SPICLOCK, OUTPUT);
  pinMode(SLAVESELECT, OUTPUT);

  digitalWrite(SLAVESELECT, HIGH); // Disable device

  SPCR = (1<<SPE)|(1<<MSTR);
  clr=SPSR;
  clr=SPDR;
  delay(10);
}

void isd_send_command(unsigned char command, unsigned int address) {
  digitalWrite(SLAVESELECT, LOW);
  spi_transfer(address & 0xff);
  spi_transfer(((address & 0xff00) >> 3) | command);
  digitalWrite(SLAVESELECT, HIGH);
}

void isd_powerdown() {
  Serial.println("Powering down...");
  isd_send_command(ISD_OPCODE_POWERDOWN, 0);
}

void isd_powerup() {
  Serial.println("Powering up...");
  isd_send_command(ISD_OPCODE_POWERUP, 0);
  delay(ISD_POWERUP_DELAY);
}

void isd_play(unsigned int address) {
  Serial.println("Playing...");
  isd_send_command(ISD_OPCODE_SETPLAY, address);
  isd_send_command(ISD_OPCODE_PLAY, 0);
}

void isd_record(unsigned int address) {
  Serial.println("Recording...");
  isd_send_command(ISD_OPCODE_SETREC, address);
  isd_send_command(ISD_OPCODE_REC, 0);
}

void isd_stop() {
  Serial.println("Stopping...");
  isd_send_command(ISD_OPCODE_STOP, 0);
}

void setup() {
  spi_init();
  Serial.begin(9600);
  isd_powerup();
}

void loop() {
  isd_record(0);
  delay(10000);

  isd_stop();
  delay(2000);

  isd_play(0);
  delay(10000);

  isd_stop();
  delay(2000);
}