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11. Processor Devices
11.1. Model for Processor Devices
The SCSI processor device is a target with the characteristics of a primary
computing device, typically a personal computer, minicomputer, mainframe
computer, or auxiliary computing device or server. Such a primary computing
device is often called a host. The processor device receives or provides
packets of data as requested by the initiator.
In the SCSI processor device, the target accepts and provides the data
packets transferred according to the commands of the initiator. The initiator
and the processor device are both assumed to know the rules by which
information is exchanged between them, how the information is interpreted by
the processor device, and when it is allowable to exchange the information.
These rules are not specified by this standard.
The initiator requests that the processor device accept a packet of data by
transmitting a SEND command. The initiator requests that the processor device
return a packet of data by transmitting a RECEIVE command. A COPY command can
also be transmitted to the processor device to request that it serve as a copy
manager. The actual data flow can be between the processor device and another
SCSI device or can be between two SCSI devices under control of the processor
device acting as a copy manager.
If a processor device temporarily has no resource available to manage a data
packet from the initiator, has no data packet to provide to the initiator, or
has no resources assigned to perform the operation, the device may then choose
one of the following responses:
1) Terminate the command with CHECK CONDITION status and the sense key NOT
READY with the appropriate additional sense code for the condition. This is
the appropriate response to a TEST UNIT READY command.
2) Disconnect until the necessary resource or data packet becomes available,
and then reconnect to the initiator and resume the operation.
3) Terminate the command with BUSY status.
More than one Logical Unit can be implemented by a processor device.
Logical Units can serve as additional paths to a single resource, and/or each
logical unit can serve as a path to different resources within the device. A
single logical unit may also serve as a path to multiple resources if the
processor device can interpret information within the data packet and route
the packet to the appropriate resource. If the logical unit addressed by the
initiator does not have an available resource or data packet associated with
it, the processor device may choose to treat the logical unit as an invalid
logical unit (see 6.5.3) or respond as described in the previous paragraph.
If the processor device determines that an error or unusual condition has
occurred while performing an operation specified by the contents of a data
packet, the information describing the condition is normally returned as a
part of a data packet. If the processor device determines that an error or
unusual condition has occurred while executing the SCSI command from the
initiator, the command is terminated with a CHECK CONDITION and the failures
are identified through a REQUEST SENSE command.
The SCSI processor device is distinguished from a SCSI communications device
by the fact that the primary destination of the data packets is within the
target device. A SCSI communications device, in contrast, passes the data on
to an ultimate destination outside the target through a network. Many types
of devices may find it convenient to function as processor devices if no other
suitable SCSI device type exists and if the packet exchange protocol dictated
by the processor device model meets their functional requirements. Devices
requiring totally incompatible protocols and command sets should be examined
carefully to be sure that the incompatibilities are based on functional
requirements. If they are, they should be treated as vendor unique device
types.
Several examples of processor device implementations are provided to clarify
the range of utility of the SCSI processor device.
11.1.1. Host to Host Communication, SEND Only
A host system, (Host A), takes the initiator role and selects a processor
device (Host B), transmitting a packet to Host B using the SEND command. The
SEND command contains an operating system call that requests data from the
local storage devices attached to Host B. After performing the functions
required by the data packet, Host B assumes the initiator mode and selects
Host A as a processor device and uses a SEND command to transmit the requested
data back to Host A. Host A thus acts as a primary computer and Host B as a
specialized data server computer. Note that the SEND command is sufficient to
perform a complete transaction if both Host A and Host B are capable of acting
as initiators. This provides the capability of a high bandwidth inter-
communication among nearby host processors.
11.1.2. Host to Host Communication, SEND and RECEIVE
A host system (Host A) takes the initiator role and selects a processor
device (Host B), transmitting a packet using the SEND command to Host B
containing instructions about an operation to be performed. Host A again
takes the initiator role and sends the data to be used by Host B in the
operation. Host A then assumes that a result will be obtained consistent with
rules understood by both devices. Host A generates a RECEIVE command to
obtain the result from Host B. If the result is not yet ready, Host B may
disconnect until the calculation is complete and the requested data packet can
be returned to Host A. Note that Host A need not support target mode and Host
B need not support initiator mode to successfully complete an exchange between
the two devices.
11.1.3. Host to Special Output Peripheral
A special co-processor device which can use the processor device command set
is a high performance graphics display terminal. The initiator sends control
and data packets to the display terminal that contain the image to be
displayed. Only the SEND command would be required. A peripheral failure
would be indicated through the normal CHECK CONDITION / REQUEST SENSE
protocol.
11.1.4. Host to Special Input Peripheral
A second special co-processor device which can use the processor device
command set is a data acquisition subsystem. Such subsystems may multiplex
and compact streams of data from many sources. A host could control the data
acquisition modes and the selection of data streams by transmitting control
packets to the processor device using the SEND command. The host could then
obtain the acquired data by executing a series of RECEIVE commands. The data
acquisition device could also serve as an initiator, selecting peripheral
storage devices and storing the compacted acquired data there for later access
directly by the host or through Host to Host communication protocols. A
peripheral failure would be indicated through the normal CHECK CONDITION /
REQUEST SENSE protocol.
11.2. Commands for Processor Devices
The commands for processor devices shall be as shown in Table 11-1.
Table 11-1: Commands for Processor Devices
==============================================================================
Operation
Command Name Code Type Section Page
------------------------------------------------------------------------------
CHANGE DEFINITION 40h O 7.2.1
COMPARE 39h O 7.2.2
COPY 18h O 7.2.3
COPY AND VERIFY 3Ah O 7.2.4
INQUIRY 12h M 7.2.5
LOG SELECT 4Ch O 7.2.6
LOG SENSE 4Dh O 7.2.7
READ BUFFER 3Ch O 7.2.12
RECEIVE 08h O 11.2.1
RECEIVE DIAGNOSTIC RESULTS 1Ch O 7.2.13
REQUEST SENSE 03h M 7.2.14
SEND 0Ah M 11.2.2
SEND DIAGNOSTIC 1Dh M 7.2.15
TEST UNIT READY 00h M 7.2.16
WRITE BUFFER 3Bh O 7.2.17
==============================================================================
Key: M = Command implementation is mandatory.
O = Command implementation is optional.
The following operation codes are vendor specific: 02h, 05h, 06h, 09h, 0Ch,
0Dh, 0Eh, 0Fh, 10h, 11h, 13h, 14h, 19h, C0h through FFh. All remaining
operation codes for processor devices are reserved for future standardization.
11.2.1. RECEIVE Command
Table 11-2: RECEIVE Command
==============================================================================
Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
Byte | | | | | | | | |
==============================================================================
0 | Operation Code (08h) |
-----|-----------------------------------------------------------------------|
1 | Logical Unit Number | Reserved |
-----|-----------------------------------------------------------------------|
2 | (MSB) |
-----|--- ---|
3 | Allocation Length |
-----|--- ---|
4 | (LSB) |
-----|-----------------------------------------------------------------------|
5 | Control |
==============================================================================
The RECEIVE command (Table 11-2) requests the target transfer data to the
initiator. The contents of the data are not defined by this standard.
11.2.2. SEND Command
Table 11-3: SEND Command
==============================================================================
Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
Byte | | | | | | | | |
==============================================================================
0 | Operation Code (0Ah) |
-----|-----------------------------------------------------------------------|
1 | Logical Unit Number | Reserved | AEN |
-----|-----------------------------------------------------------------------|
2 | (MSB) |
-----|--- ---|
3 | Transfer Length |
-----|--- ---|
4 | (LSB) |
-----|-----------------------------------------------------------------------|
5 | Control |
==============================================================================
The SEND command (Table 11-3 requests the target transfer data from the
initiator.
An asynchronous event notification (AEN) bit of one indicates that the data
to be transferred conforms to AEN data format as defined in Table 11-4. A
SEND command with an AEN bit of one shall only be issued to logical unit zero.
An AEN bit of zero indicates that the data to be transferred are vendor-
specific.
The transfer length specifies the length in bytes of data that shall be sent
during the DATA OUT phase. A transfer length of zero indicates that no data
shall be sent. This condition shall not be considered as an error.
Table 11-4: SEND Command - AEN Data Format
==============================================================================
Bit| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
Byte | | | | | | | | |
==============================================================================
0 | Reserved | LUNTAR | Reserved | LUNTRN |
-----|-----------------------------------------------------------------------|
1 | Reserved |
-----|-----------------------------------------------------------------------|
2 | Reserved |
-----|-----------------------------------------------------------------------|
3 | Reserved |
-----|-----------------------------------------------------------------------|
4 to| Sense Data Byte (0) |
- - -|- - - -|
n+4 | Sense Data Byte (n) |
==============================================================================
A logical unit target (LUNTAR) bit of zero specifies that the asynchronous
event occurred on a logical unit. A LUNTAR bit of one specifies that the
asynchronous event occurred on a target routine.
If the LUNTAR bit is zero, the logical unit number target routine number
(LUNTRN) field specifies on which logical unit the asynchronous event
occurred. If the LUNTAR bit is one, the LUNTRN field specifies on which
target routine the asynchronous event occurred.
The sense data bytes are defined in Table 7-35.
11.3. Parameters for Processor Devices
11.3.1. Diagnostic Parameters
This section defines the descriptors and pages for diagnostic parameters
used with processor devices.
The diagnostic page codes for processor devices are defined in Table 11-5.
Table 11-5: Diagnostic Page Codes
==============================================================================
Page Code Description Section
------------------------------------------------------------------------------
00h List of Supported Parameters Page 7.3.1.1
01h - 3Fh Reserved (for all device type pages)
40h - 7Fh Reserved
80h - FFh Vendor-specific pages
==============================================================================
11.3.2. Log Parameters
This section defines the descriptors and pages for log parameters used with
processor devices.
The log page codes for processor devices are defined in Table 11-6.
Table 11-6: Log Page Codes
==============================================================================
Page Code Description Section
------------------------------------------------------------------------------
01h Buffer Over-Run/Under-Run Page 7.3.2.1
07h Last n Error Events Page 7.3.2.3
00h List of Supported Parameters Page 7.3.2.5
06h Non-Medium Error Page 7.3.2.4
02h - 05h Reserved
08h - 2Fh Reserved
30h - 3Eh Vendor-specific pages
3Fh Reserved
==============================================================================
11.4. Glossary for Processor Devices
host. A device with the characteristics of a primary computing device,
typically a personal computer, workstation, minicomputer, mainframe computer,
or auxiliary computing device or server.
data packet. The data transferred during the DATA IN phase of a RECEIVE
command, or during the DATA OUT phase of a SEND command. A data packet often
contains information at the beginning or end of the packet that describes the
contents of the packet. A data packet might contain control or status
information for the destination device.
resource. A part of the device required to operate on or store the data
packet.
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