152 Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E
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[3] The Buffer Full Ratio indicates, on Read commands, how full the disc drive’s buffer shall be before
attempting a reselection. The disc drive rounds the requested ratio up to the nearest whole logical block.
This value is changeable by an initiator.
The buffer full ratio is taken to be a percentage of the smaller of
a) the buffer size
or
b) the remaining transfer length.
For example, if the buffer full ratio is 80h (128 Decimal) (indicating a 128/256 or 50% value), the transfer
length of a read command is 20h blocks, and the buffer size is 30h blocks, the reconnect begins when
10h blocks (50% of the transfer length of 20h blocks) is in the buffer.
[4] The Buffer Empty Ratio indicates, on Write commands, how empty the disc drive’s buffer shall be before
attempting a reselection. The disc drive, rounds the requested ratio down to the nearest whole logical
block. This value is changeable by an initiator.
[5] The Bus Inactivity Limit field (bytes 4 & 5) indicates the time, in 100 microsecond increments, the disc
drive is allowed to assert the Busy signal without handshakes until it shall disconnect. The value of ten
indicates the disc drive is allowed to maintain the Busy signal for one millisecond without handshakes. A
value of zero indicates that there is no bus inactivity limit. This value is not changeable by the initiator.
[6] The Disconnect Time Limit field (bytes 6 and 7) indicates the minimum time, in 100 microsecond incre-
ments, the disc drive shall remain disconnected until it shall attempt to reconnect. A value of zero indi-
cates the disc drive is allowed to reconnect immediately. For the typical disc drive, this is likely to always
be zero and the changeable code is always zero. (See individual Product Manual).
[7] The Connect Time Limit field (bytes 8 and 9) indicates the maximum time in 100 microsecond increments
that the target should remain connected until it attempts to disconnect. A setting of zero indicates that the
disc drive is allowed to remain connected indefinitely until it attempts disconnection.
[8] The maximum burst size field indicates the maximum amount of data that the target shall transfer during
a data phase before disconnecting if the initiator has granted the disconnect privilege. This value is
expressed in increments of 512 bytes (e.g., a value of one means 512 bytes, two means 1024 bytes,
etc.). A value of zero indicates there is no limit on the amount of data transferred per connection.
[9] The data transfer disconnect control (DTDC) field is intended to define further restrictions on when a
disconnect is permitted. A value of 000b indicates the field is not used.
[10] The Enable Modify Data Pointers (EMDP) bit indicates whether or not the initiator allows the Modify Data
Pointers message to be sent by the target. If the EMDP bit is zero, the target shall not issue the Modify
Data Pointers Message. If the EMDP bit is one, the target is allowed to issue Modify Data Pointers
Message.
[11] DImm: Disconnect Immediate. Not used at this time.
