Specifications

ATAPI For Streaming Tape QIC-157 Rev B
1
1. ATAPI Overview
The purpose of the ATAPI is to provide a more extensible and general purpose interface than the
ATA Task file.
Although the attachment of a Streaming Tape on the ATAPI Interface will utilize the ATA Host
Hardware and Task File, the logical interface will differ slightly and will need to support additional
capabilities. The Mass Storage devices connected to the ATA make use of eight registers (Task
File) that contain the command and all parameters needed for operation. However, eight registers is
not enough to pass all the needed information for commanding other peripheral types. To remedy
this, the ATAPI Device will receive its commands through the use of a Packet mode, in addition to
the normal ATA protocol. The Packet Command will complement the existing ATA commands.
The ATAPI Device shall support all of the ATA specified protocol, including the Reset
Master/Slave Diagnostic Sequence, Diagnostic Command, and Command Abort for unsupported
Commands. The ATAPI Device shall also support both the Master and Slave modes of operation.
1.1. ATA Signal Utilization
ATAPI Devices shall utilize the same signals and timing from the ATA Standard and Extensions.
1.2. ATA Command Utilization
The ATA Task File concept does not contain enough bytes to support some of the Streaming Tape
command structures, so a new command called “Packet Command” has been added to allow a
Packet to be sent to the Device. The Packet shall be transferred by writing multiple times to the
Data Register. No random access to the register file in the Peripheral can be done. This technique
reduces the number of register addresses needed, but not the actual space needed. Although all the
commands for the Device could be sent via this packet mode, it is believed that some of the existing
ATA commands and the full ATA command protocol must be provided for the existing drivers to
operate correctly. The Device will therefore support some existing ATA commands in addition to
the new “Packet command”, so that there will be minimal changes to the existing drivers. This
minimal set of ATA commands is different than the minimum as defined in the ATA standard, but
should be sufficient for normal operation.
1.3. ATA Compatibility
There are several backward compatibility issues with the existing ATA commands, and therefore
the ATAPI Device shall respond to the existing ATA Reset Master/Slave Diagnostic Sequence, but
not the Identify Drive or Read commands. This will allow the BIOS and older drivers to ignore the
ATAPI Device and not confuse ATAPI data with normal ATA Drive format data. All unsupported
ATA commands shall be Aborted, and not executed. As with aborted commands in ATA, an
interrupt shall be generated to signal the completion with an “Aborted” error status.