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T13/2132-D Revision 3 June 23, 2010
66 Working Draft Enhanced Disk Drive - 4 (EDD-4)
8.27 Send Packet Command (FN 50h)
8.27.1 Overview
This function defines a service that the system BIOS shall call for sending data to and from a device
implementing a protocol using packet transfers. The BIOS shall provide this service before the OS is loaded.
When an operating system takes control of the device controller it replaces the BIOS routine for this service to
provide a seamless transfer of control from the BIOS to the operating system. This service allows several BIOS
level services to continue functioning, even after the OS has taken control of the device controller, for example:
a) The INT 13h mass storage interface
b) Power Management
c) Suspend to disk
The BIOS is single threaded. This means that the BIOS shall not process asynchronous requests from other
devices. The BIOS shall send commands to devices and wait for responses. This means that the operating
system may take control of the serial interface with no hand-off information from the system BIOS. The
operating system shall reconfigure the interface and hook the service described above. The system BIOS may
provide INT 13h FN 50h for the 1394, USB, and any other packet oriented bus.
The format of the packet shall be determined by the requirements of the target bus and is beyond the scope of
this document. In the case of USB, the packet format shall be determined by the USB specification. In the case
of 1394, IEEE 1394-1995 shall determine the size of a packet with payload information defined in SBP-2.
8.27.2 Packet Sending Service (PSS) For SCSI Command Descriptor Blocks (CDB)
8.27.2.1 Overview
The purpose of the PSS is to allow an application to send SCSI CDB's using BIOS INT 13h calls to a device,
regardless of the bus on which the device resides. This interface is currently defined for ATAPI, SCSI, 1394, and
USB devices. Future buses that use SCSI CDB's may also adopt this mechanism for transporting commands
This interface shall not retry any operation. If an error occurs either in command format, or operation of the
device, an error shall be returned by INT 13h. The application may choose to retry a command by issuing it
again.
Entry
AH 50h
AL D7h
DL BIOS device number
ES:SI Pointer to formatted command packet (see table 30)
Exit
Carry Clear Function completed without error
AH Shall be cleared to zero
Carry Set Function completed with an error
AH AH = 01 - Function not implemented, 80h - Command failed to complete, 97h
- Subfunction D7h not supported for this device, C3h - Formatted Command
Packet is too short
Table 30 — Formatted Command Packet
Offset Type Description
0 Word Length of this record in bytes
2-n Byte Formatted protocol specific data