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
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
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.
User’s Guide | 21020285 D |
