20 Unit Options (08H)

RCE Retry Command Errors - Allows you to select whether the adapter will respond to a device error with a retry of the failed command.

0 ⇒ Do not retry for device errors.

1 ⇒ Retry commands that error from the device.

RBE Retry Bus (SCSI) Errors - Enables retries in the event that a command fails.

0 ⇒ Do not perform Bus Error retries. 1 ⇒ Perform Bus Error retries. Select Time-out

According to SCSI specifications, a target must respond to initiator selection by asserting the BSY signal in response to SEL, with its ID on the bus. With this field you can select the amount of time that the RF3880 adapter will wait for response before timing out with an error.

The select time-out period is specified in 1 millisecond increments. The default value is 250 (FAH), which selects a period of 250 milliseconds.

The longest time-out period possible is 392 milliseconds, selected with a value of 392 (188H) Any larger value placed in this field will still select 392 milliseconds.

A value of 0 will select the shortest time-out period possible, which is about 1 millisecond.

Unit Flags

The Unit Flags field of the Unit Options Parameter Block is where you can define command operation for the unit. With bit settings you can address the issues of: synchronous data transfer, tagged commands, and use of the ATN signal.

Note

If you set the TAG flag (explained below) the adapter will ignore the UNQ bit. Setting the TAG bit implies that you are using a SCSI-2 or SCSI-3 device. The UNQ bit is intended for SCSI-1 devices.

UNQ Untagged Queuing - The SCSI-1 specification allows issue of multiple, simultaneous, commands to a target that has multiple LUN’s, one command per LUN. This bit allows you to select whether the RF3880 will queue commands to a target with multiple LUN’s.

0 ⇒ Send one command at a time to this target.

1 ⇒ Queue commands to this target; it has multiple LUN’s.

SYN Synchronous Negotiation - Either the initiator or the target may introduce negotiation for synchronous operation. How you set this bit determines whether the RF3880 adapter will attempt to negotiate with the device. (Even if you do not set this bit to allow negotiation, if the other device begins negotiation, the adapter will respond.)

0 ⇒ Do not initiate negotiation for synchronous data transfer. 1 ⇒ Negotiate for synchronous data transfer.

BITS

7 6 5 4 3 2 1 0

0 TAG 0 0 WID IAT SYN UNQ

Unit Options (08H) Page 7 - 21

IAT Inhibit ATN Signal - With this bit you can select whether the adapter will assert the ATN signal during selection of a target. (Some older SCSI devices do not respond to the ATN signal and may stop executing commands if it is asserted.) Setting this bit will prevent the adapter from negotiating for synchronous transfers, wide transfers, and SCSI-2 features. Parity checking will also be disabled. If you enable any of these features with this bit set, you will get errors.

0 ⇒ ATN will be asserted.

1 ⇒ ATN will not be asserted during target selection.

WID Wide Transfers - Either the initiator or the target may introduce negotiation for wide data transfers. How you set this bit determines whether the RF3880 adapter will attempt to negotiate with the device. (Even if you do not set this bit to allow negotiation, if the other device begins negotiation, the adapter will respond.)

0 ⇒ Do not initiate negotiation for wide data transfer 1 ⇒ Negotiate for wide data transfer.

TAG - The function of this bit varies depending upon whether the adapter is in initiator or target mode.

Initiator Mode

Tagged Queuing - One of the design options offered with the SCSI-2 specification is the capability to issue multiple simultaneous commands to each logical unit. If you have a peripheral that is designed to this specification, you can use this bit to tell the RF3880 adapter to negotiate for tagged queuing. The tag “type” is specified in the Flags-2 field of the Pass-through command Parameter Block. Refer to Chapter 5. 0 ⇒ Tagged queuing operation not negotiated.

1 ⇒ Peripheral supports tagged queuing - negotiate for it. Target Mode

Selection of Group 2 Commands - During Target Mode

operations, the Tag bit controls whether Group 2’s 6- or 10-byte SCSI-2 commands are accepted.

0 ⇒ 6-byte commands accepted; no SCSI-2 devices configured. 1 ⇒ 10-byte commands accepted; SCSI-2 devices configured. Sense Count

The RF3880 adapter automatically responds to a device Check Condition with a SCSI Request Sense command. (Unless inhibited on a per command basis with the IRS bit of the Flags-1 field which is embedded in the SCSI Pass- through command Parameter Block. See Chapter 5.)

The Request Sense command, issued by the adapter to the device with the Check Condition, can garner Sense information of up to 256 bytes. The number returned depends on the number asked for in the SCSI Request Sense command. The Sense Count field is used to define the number of Sense bytes the adapter will ask for when automatically issuing a Request Sense command.