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User’s Guide 21020285 D
Chapter 4 Command Operation
What the Adapter must accomplish Page 4 - 3
What the
Adapter must
accomplish
There are several basic operational requirements that the RF3880 adapter must
fulfill:
The Host must have a method to communicate details of command
operation with the adapter — Communication from the host to the RF3880
adapter takes the form of command structures. There are two types of command
structures you can use with the RF3880 adapter: Single Command and
Command List. The latter is preferable in most situations because it boosts the
performance of the adapter. There are instances when you must use the single
command method of communication. Both types of structures are described in
the following sections.
The adapter must have a means to communicate the outcome of a
command process — Reporting the completion status of the command is
accomplished via status blocks which are part of the command structure. Just
as there are two types of RF3880 command structures for you to use when
issuing a command, there are two ways status structures are returned from the
adapter. Each uses slightly different protocol to notify the Host of returned
status. This is described in more detail in a later section.
The Host must have a way to alter the behavior of the adapter to
suit its environment — To meet the versatility required by differing host
operating systems and application needs, the RF3880 adapter has a set of board
level commands for you to use. These commands allow you to select options
relating to the system bus of the host and also tailor operation for the devices
attached to the board. They are referred to as Board-control commands.
The Host must have a defined protocol for issuing commands to
the adapter (acting as an initiator or a target) — The RF3880 adapter
is an interface between the VMEbus and SCSI bus architectures. When the
VMEbus Host requests an operation involving the SCSI bus, the RF3880 issues
a command to a device on the bus, using SCSI protocol, or acts as the
intermediary for an initiator on the bus. The RF3880 uses the defined SCSI
command structure within its own parameter-block command structure. This
allows the RF3880 to pass commands to the SCSI device without modification
(in Initiator Mode) or receive a SCSI command and pass it to the Host for
interpretation (in Target Mode). These are called Pass-through commands.
The adapter must provide status from a device regarding the
command just completed by the device — Just as the defined SCSI
command structure is part of the RF3880 command structure and is passed
through to the device, the Sense Bytes from the SCSI device are reported to the
host within the Status Block returned by the adapter.
Each of these operational requirements is discussed in more detail on the
following pages.