17. ATA Driver


The ATA/IDE Drivers are out of date and should not be used for new BSPs. The preferred alternative is to port the ATA/SATA/SCSI/NVMe support from FreeBSD to RTEMS using the libbsd. Ask on the mailing list if you plan to write a driver for an ATA/IDE device.

17.1. Terms

ATA device - physical device attached to an IDE controller

17.2. Introduction

ATA driver provides generic interface to an ATA device. ATA driver is hardware independent implementation of ATA standard defined in working draft “AT Attachment Interface with Extensions (ATA-2)” X3T10/0948D revision 4c, March 18, 1996. ATA Driver based on IDE Controller Driver and may be used for computer systems with single IDE controller and with multiple as well. Although current implementation has several restrictions detailed below ATA driver architecture allows easily extend the driver. Current restrictions are:

  • Only mandatory (see draft p.29) and two optional (READ/WRITE MULTIPLE) commands are implemented
  • Only PIO mode is supported but both poll and interrupt driven

The reference implementation for ATA driver can be found in cpukit/libblock/src/ata.c.

17.3. Initialization

The ata_initialize routine is responsible for ATA driver initialization. The main goal of the initialization is to detect and register in the system all ATA devices attached to IDE controllers successfully initialized by the IDE Controller driver.

In the implementation of the driver, the following actions are performed:

rtems_device_driver ata_initialize(
  rtems_device_major_number  major,
  rtems_device_minor_number  minor,
  void                      *arg
  initialize internal ATA driver data structure

  for each IDE controller successfully initialized by the IDE Controller driver
    if the controller is interrupt driven
      set up interrupt handler

    obtain information about ATA devices attached to the controller
    with help of EXECUTE DEVICE DIAGNOSTIC command

    for each ATA device detected on the controller
      obtain device parameters with help of DEVICE IDENTIFY command

      register new ATA device as new block device in the system

Special processing of ATA commands is required because of absence of multitasking environment during the driver initialization.

Detected ATA devices are registered in the system as physical block devices (see libblock library description). Device names are formed based on IDE controller minor number device is attached to and device number on the controller (0 - Master, 1 - Slave). In current implementation 64 minor numbers are reserved for each ATA device which allows to support up to 63 logical partitions per device.

controller minor device number device name ata device minor
0 0 hda 0
0 1 hdb 64
1 0 hdc 128
1 1 hdd 172

17.4. ATA Driver Architecture

17.4.1. ATA Driver Main Internal Data Structures

ATA driver works with ATA requests. ATA request is described by the following structure:

/* ATA request */
typedef struct ata_req_s {
  Chain_Node        link;   /* link in requests chain */
  char              type;   /* request type */
  ata_registers_t   regs;   /* ATA command */
  uint32_t          cnt;    /* Number of sectors to be exchanged */
  uint32_t          cbuf;   /* number of current buffer from breq in use */
  uint32_t          pos;    /* current position in 'cbuf' */
  blkdev_request   *breq;   /* blkdev_request which corresponds to the ata request */
  rtems_id          sema;   /* semaphore which is used if synchronous
                             * processing of the ata request is required */
  rtems_status_code status; /* status of ata request processing */
  int               error;  /* error code */
} ata_req_t;

ATA driver supports separate ATA requests queues for each IDE controller (one queue per controller). The following structure contains information about controller’s queue and devices attached to the controller:

 * This structure describes controller state, devices configuration on the
 * controller and chain of ATA requests to the controller.
typedef struct ata_ide_ctrl_s {
  bool          present;   /* controller state */
  ata_dev_t     device[2]; /* ata devices description */
  Chain_Control reqs;      /* requests chain */
} ata_ide_ctrl_t;

Driver uses array of the structures indexed by the controllers minor number.

The following structure allows to map an ATA device to the pair (IDE controller minor number device is attached to, device number on the controller):

 * Mapping of RTEMS ATA devices to the following pairs:
 * (IDE controller number served the device, device number on the controller)
typedef struct ata_ide_dev_s {
  int ctrl_minor;/* minor number of IDE controller serves RTEMS ATA device */
  int device;    /* device number on IDE controller (0 or 1) */
} ata_ide_dev_t;

Driver uses array of the structures indexed by the ATA devices minor number.

ATA driver defines the following internal events:

/* ATA driver events */
typedef enum ata_msg_type_s {
  ATA_MSG_GEN_EVT = 1,     /* general event */
  ATA_MSG_SUCCESS_EVT,     /* success event */
  ATA_MSG_ERROR_EVT,       /* error event */
  ATA_MSG_PROCESS_NEXT_EVT /* process next ata request event */
} ata_msg_type_t;

17.4.2. Brief ATA Driver Core Overview

All ATA driver functionality is available via ATA driver ioctl. Current implementation supports only two ioctls: BLKIO_REQUEST and ATAIO_SET_MULTIPLE_MODE. Each ATA driver ioctl() call generates an ATA request which is appended to the appropriate controller queue depending on ATA device the request belongs to. If appended request is single request in the controller’s queue then ATA driver event is generated.

ATA driver task which manages queue of ATA driver events is core of ATA driver. In current driver version queue of ATA driver events implemented as RTEMS message queue. Each message contains event type, IDE controller minor number on which event happened and error if an error occurred. Events may be generated either by ATA driver ioctl call or by ATA driver task itself. Each time ATA driver task receives an event it gets controller minor number from event, takes first ATA request from controller queue and processes it depending on request and event types. An ATA request processing may also includes sending of several events. If ATA request processing is finished the ATA request is removed from the controller queue. Note, that in current implementation maximum one event per controller may be queued at any moment of the time.

(This part seems not very clear, hope I rewrite it soon)