Specifications

ATAPI For Streaming Tape QIC-157 Rev B

present, the ATAPI Driver must issue the ATAPI Device an ATAPI command, re-enabling DRDY,

before it can issue an ATA Power management command. Operating systems wishing to use a

common ATA power management Driver must also be changed to perform this detection and

recovery sequence, if they intend to power-manage ATAPI Devices.

2.14.3. Special Handling of ATA Read and Identify Drive Commands

In order to provide ATAPI Drivers with the ability to force a Device to initialize its ATAPI

signature (Cylinder High = EBh, Cylinder Low = 14h) without issuing an SRST, ATAPI Devices

shall abort the ATA Read and Identify Drive commands and initialize the task file with the ATAPI

signature before clearing BSY.

2.14.4. ATAPI aware BIOS and Driver Considerations

Pre-ATAPI BIOS will not detect or configure ATAPI Devices. Some of the BIOS is capable of

configuring ATA hard disks for ATA Mode 3 PIO & IORDY operation. This places a special

burden on ATAPI Drivers to detect the presence of any ATA disk drive sharing the same port

address and configure the ATAPI Device for a compatible mode of operation.

Note that a special IDE port configuration Driver must be provided by the IDE card manufacturer to

configure the cards proprietary IDE configuration control registers. These proprietary IDE card

Drivers should be loaded before the ATAPI Driver.

During ATAPI Device detection, ATAPI Device Drivers or ATAPI-aware BIOS should verify that

Status=00h (Not BSY, Not RDY) and that the ATAPI signature Cylinder High = EBh, Cylinder

Low = 14h are present. If an ATAPI Device is detected, then issue an ATAPI Identify Command to

complete the ATAPI detection protocol and re-enable the task file (DRDY=1). If the Device is

ready to accept an ATA command but no ATAPI signature is detected, then issue an ATA Read or

Identify Drive command to the Device to force the ATAPI Device to initialize it’s signature. Then

wait for BSY=0 and re-verify the presence of the ATAPI signature. If there is still no ATAPI

signature present, do not configure the Device.

ATAPI-aware BIOS and Drivers should give special attention to managing configurations where

ATAPI Drivers share an IDE port address (Cable) with ATA IDE Drives and their Drivers. ATA

IDE Drivers frequently issue SRSTs to manage errors thereby causing ATAPI Devices to clear

DRDY as part of their SRST ATAPI signature initialization sequence. If the ATAPI Driver already

knows that the Device it wishes to issue an ATAPI command to is an ATAPI Device, then it need

not take special action since issuing any of the ATAPI commands that do not require DRDY=1, will

restore the ATAPI Device’s ability to accept ATA commands. If, however, the ATAPI Driver

wishes to issue an ATA command to an ATAPI Device that has received an SRST from an ATA

IDE Driver, it should issue the ATAPI Device an ATAPI packet command or Identify to restore the

ATAPI Device’s ability to accept ATA commands.

Note that “Newer” BIOS detects the presence of a Drive (see 1.3 ATA Compatibility on page 1) by

using the Identify Drive command, but older BIOS use configuration information from outside the

IDE/ATA interface. It has also been discovered that very old BIOS may issue an ATA Read

command to detect the presence of an ATA IDE Drive. Therefore, the ATA Read and Identify

Drive commands shall be aborted by ATAPI Devices. It has also been discovered that some BIOS

looks at the status register to detect the presence of an ATA Drive.