scsi interface specification - Plasmon

LASER-DRIVE SCSI CHARACTERISTICSCOMMAND TIMEOUTLASER-DRIVE SCSICHARACTERISTICSThis section discusses physical characteristics and logical architecture of SCSI as applied to theLaserDrive. For general information concerning SCSI, refer to the ANSI SCSI document, X3.131-1994.COMMAND TIMEOUTCommand timeout values are dependent on the command being executed. A value of 60 sec is adequatefor all commands except for those listed in the following table. The values listed in the table should be usedwith the command length field in the CDB (bytes 7 and 8) to calculate an adequate timeout when morethan 60 sec is required. These nominal values are only guidelines and do not represent transfer rates.Actual time-out values may significantly change due to hardware and media conditions.COMMAND TYPETIMEOUT VALUEMedia Scan Command 3200 blocks/sec (1)Read Commands 1000 blocks/sec (2)Send Diagnostic Command15 min.Verify Commands 1200 blocks/sec (2)Write Commands 1150 blocks/sec (2)Write/Verify Commands 400 blocks/sec (2)(1) This value was measured for a sequential scan of a completely blank mediasurface. Overhead was added for processing and media management.(2) These values do not include Map Read times.SCSI BUS CONDITIONSThe SCSI bus has two asynchronous conditions: ATTENTION and RESET. These conditions cause theLaserDrive to perform certain actions and can alter the phase sequence.ATTENTION CONDITIONThe ATTENTION condition allows an Initiator to inform the LaserDrive that the Initiator has a messageready. The LaserDrive receives this message by performing a MESSAGE OUT phase.The Initiator creates the ATTENTION condition by asserting ATTN at any time except during theARBITRATION or BUS FREE phases.The Initiator should assert the ATTN signal before releasing ACK for the last byte transferred in a busphase so the ATTENTION condition can be honored before a transition to a new bus phase. An ATTNasserted later might not be honored until a later bus phase and then may result in an unexpected action.The LaserDrive responds with MESSAGE OUT phase as follows:97653978 HPage 9