User`s manual

Overview
2-4 Single Board Computers SCSI Software UserÕs Manual
2
Primary Functions of the Firmware
The Firmware is designed to manage the SCSI bus protocol when interfacing
to a device on the SCSI bus. The Firmware operates independently of any
specific knowledge of devices on the SCSI bus.
The Firmware handles the following aspects of SCSI protocol.
❏ Interpret Received Messages
The Firmware automatically receives and processes the messages received
from target devices.
❏ Send Required/Response Messages
The Firmware generates and sends any required messages, such as
identify , during the course of command processing. The Firmware also
generates and sends messages in response to received messages (e.g.,
synchronous data transfer request message exchange).
❏ Phase Transition Handling
The Firmware automatically handles all phase transitions that occur
during the normal course of interfacing to a SCSI device.
For example, the Firmware transitions through the following bus phases
to execute a single SCSI read command to a disk drive: ARBITRATION,
SELECTION (WITH ATTENTION), MESSAGE (identify), COMMAND,
DATA-IN, STATUS, MESSAGE (command complete), and BUS FREE. In
addition to this minimal set of phase transitions, the device may
disconnect and reconnect several times during the DATA-IN phase. The
Firmware handles each of these phase changes without direct intervention
from the user.
❏ Multi-Threaded Command Management
The Firmware manages multiple threading of commands to the SCSI bus.
SCSI protocol allows for all devices attached to the bus to have
simultaneously outstanding commands. The logical and physical thread
management used to facilitate this multiple threading is handled by the
Firmware and is transparent to the user.
❏ Device Queue Management
The Firmware provides a command queue management scheme that
allows the user to send an unlimited number of command requests to a
device before receiving status for any of them.