Specifications

ATAPI For Streaming Tape QIC-157 Rev B

3. ATAPI Transport Mechanism

The Transport Mechanism provides for the hardware support to connect the Host Computer to the

Peripheral. There will ultimately be two “Models” of operation specified, the Compatibility and

Extended Capability Models. The Compatibility Model will look exactly like an ATA/IDE Drive to

all existing Drivers, Operating Systems and Hardware. It will operate under many restrictions and

will be required to support extra capabilities. The Extended Capability Model will be used to

address issues, such as IRQ sharing and multi-threading of commands. The Extended Capability

Model will be defined at a later time and will not be defined in this specification. The Compatibility

Model is described in the remainder of this section.

3.1. Reset Conditions

There are three types of Reset Condition to which ATAPI Devices shall respond:

• Power On Reset or Hardware Reset: the Device executes a series of electrical circuitry

diagnostics and sets default values, as well as executing the Master Slave Diagnostic Protocol.

• ATAPI Soft Reset: ATAPI Devices shall reset the interface circuitry according to the Set

Features requirement upon receipt of the ATAPI Soft Reset Command.

• ATA SRST: ATAPI Devices shall provide the normal ATA PDIAG/ DASP sequence and

initialize the task file with the ATAPI signature upon detection of SRST. No actual reset of the

ATAPI Device shall occur and the DSC bit in the Status Register shall be cleared if any

commands are active. Active commands shall not be aborted or stopped.

The Reset Conditions above are listed in order of precedence. That is, Power On or Hardware Reset

shall take precedence over ATAPI Soft Reset, which shall take precedence over ATA SRST, which

shall take precedence over all other conditions.

3.1.1. Power On or Hardware Reset

Each ATAPI Device, as it is powered on, shall perform appropriate internal reset operations, and

internal test operations.

ATAPI Devices upon detection of reset, shall:

1. Clear all Commands and I/O operations in progress.

2. Return to Device's default configuration.

3. Perform the DASP/PDIAG sequence.

4. Return any ATAPI Device operating modes to their appropriate initial conditions, similar to

those conditions that would be found after a normal power-on reset. MODE SELECT conditions

shall be restored to their last saved values if saved values have been established. MODE

SELECT conditions for which no values have been saved shall be returned to their default

values.

5. Initialize the Task File Registers as follows: Status = 00h, Error = 01h, Sector Count = 01h,

Sector Number = 01h, Cylinder Low = 14h, Cylinder High =EBh and Drive/Head = 00h. A

value other than 00 in the status register prior to the receipt of the first ATAPI Command Packet

from the Host may cause the ATAPI Device to be incorrectly identified by the Host as an ATA

compatible disk Drive. BSY = 0, following any Reset, indicates to the Host that the registers

within the Task File have been initialized.