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// Initialize disk
  detect_and_init();
  // reset_controller();

  select_drive(MASTER_DRIVE);
  read_pio(1, 10, 0);

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void read_pio(uint16_t sector_count, uint32_t LBA_low4, uint16_t LBA_high2){

  // Read LBA mode
  // @TODO this assumes master drive
  outb(PRIMARY_BUS_PORT_BASE + DRIVE_HEAD_REG_OFF, LBA_MODE);

  // Sectorcount high byte
  outb(PRIMARY_BUS_PORT_BASE + SECT_COUNT_REG_OFF, (sector_count >> 8) & 0xFF);

  // LBA bytes 4, 5, 6
  outb(PRIMARY_BUS_PORT_BASE + LBA_LO_REG_OFF, (LBA_low4 >> 24) & 0xFF);
  outb(PRIMARY_BUS_PORT_BASE + LBA_MID_REG_OFF, (LBA_high2) & 0xFF);
  outb(PRIMARY_BUS_PORT_BASE + LBA_HI_REG_OFF, (LBA_high2 >> 8) & 0xFF);

  // Sectorcount low byte
  outb(PRIMARY_BUS_PORT_BASE + SECT_COUNT_REG_OFF, (sector_count) & 0xFF);

  // LBA bytes 1, 2, 3
  outb(PRIMARY_BUS_PORT_BASE + LBA_LO_REG_OFF, (LBA_low4) & 0xFF);
  outb(PRIMARY_BUS_PORT_BASE + LBA_MID_REG_OFF, (LBA_low4 >> 8) & 0xFF);
  outb(PRIMARY_BUS_PORT_BASE + LBA_HI_REG_OFF, (LBA_low4 >> 16) & 0xFF);

  // Read sectors command
  outb(PRIMARY_BUS_PORT_BASE + CMD_REG_OFF, READ_SECTORS_EXT);

  // Poll for DRQ -- when uncommented, this works, DRQ is set
  // if (ata_wait(DRQ, ATA_WAIT)) {
    // read_sectors();
 // }
}

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// Returns status (1 = success, 0 = failure)
uint8_t select_drive(uint8_t drive){

  uint8_t status;

  // No matter which drive is requested, we first must check the
  // status of the currently selected drive to make sure that it
  // is not actively modifying status
  status = inb(PRIMARY_BUS_PORT_BASE + STATUS_REG_OFF);
  uint8_t mask = BSY | DRQ | ERR;
  if (status & mask){
    printf("Not ready to select drive\n");
    return 0;
  }

  // Already selected, nothing to do
  if (drive == CURRENT_DRIVE){
    return 1;
  }

  // Select drive, then delay 400ns
  outb(PRIMARY_BUS_PORT_BASE + DRIVE_HEAD_REG_OFF, drive);
  for (int i = 0; i < 4; i++){
    inb(PRIMARY_BUS_ALT_STATUS);
  }

  // Read the Status register to clear pending interrupts
  // Ignore value
  inb(PRIMARY_BUS_PORT_BASE + STATUS_REG_OFF);

  // Read Status register one more time, use this to determine status
  status = inb(PRIMARY_BUS_PORT_BASE + STATUS_REG_OFF);

  if (status & mask){
    printf("Drive select failed\n");
    return 0;
  }
  
  CURRENT_DRIVE = drive;
  return 1;
}

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// ----------------------------------------
// Controller I/O Port Registers
// ----------------------------------------

#define PRIMARY_BUS_PORT_BASE       0x1F0
#define PRIMARY_BUS_ALT_STATUS      0x3F6

#define MASTER_DRIVE 0xA0

// IO Port register offsets
#define DATA_REG_OFF        0x0
#define ERR_REG_OFF         0x1
#define FEATURE_REG_OFF     0x1
#define SECT_COUNT_REG_OFF  0x2
#define LBA_LO_REG_OFF      0x3
#define LBA_MID_REG_OFF     0x4
#define LBA_HI_REG_OFF      0x5
#define DRIVE_HEAD_REG_OFF  0x6
#define STATUS_REG_OFF      0x7
#define CMD_REG_OFF         0x7

// ----------------------------------------
// Command Port Commands
// ----------------------------------------

#define READ_SECTORS_EXT  0x24

// ----------------------------------------
// Status Register Bitflag Codes
// ----------------------------------------

#define ERR  0x1   // Indicates an error occurred. Send new cmd to clear
#define DRQ  0x8   // Set when drive has PIO dat to transfer, or is ready to accept PIO data
#define SRV  0x10  // Overlapped Mode Service Request
#define RDY  0x40  // Bit is clear when drive is spun down or after err. Set otherwise
#define BSY  0x80  // Indicates drive is preparing to send/receive data (wait for it to clear). 

#define INVALID_ATA_STATUS 0xFF

// ----------------------------------------
// Read / Write Constants
// ----------------------------------------

#define LBA_MODE  0x40

// Polling mode, either once or immediate
#define ATA_ONCE  0x0
#define ATA_WAIT  0x1

extern uint8_t CURRENT_DRIVE;