5.3 Terminal Function Codes

Eight function modifiers can be specified with IO$_READVBLK, IO$_READLBLK, and IO$_READPROMPT. Table 5-6 lists these function modifiers and IO$_EXTEND, which is described in Section “Itemlist Read Operations”. All read function modifiers are supported for LAT devices.

The P4 argument to a read QIO function either specifies the terminator set for the read function or points to the location containing the terminator set. If P4 is 0, all ASCII characters with a code in the range 0 through 31 (hexadecimal 0 through 1F), except LF, VT, FF, TAB, and BS, are terminators (see Appendix C). This is the RMS standard terminator set. The delete character (hexadecimal 7F) and 8-bit controls in the range 128 through 159, and 255 (hexadecimal 80 through 9F, and FF) are also terminators. If line editing is enabled, only Return, Ctrl/Z, or an escape sequence terminates a read operation.

If P4 does not equal 0, it contains the address of a quadword that either specifies a terminator character bit mask or points to a location containing that mask. (Note that if P4 references an address in a MACRO program, a number sign (#) must precede the address; for example, P4=#TMASK.) The quadword has a short form and a long form, as shown in Figure 5-3. In the short form, the correspondence is between the bit number and the binary value of the character; the character is a terminator if the bit is set. For example, if bit 0 is set, NULL is a terminator; if bit 9 is set, TAB is a terminator. If a character is not specified, it is not a terminator. Since ASCII control characters are in the range 0 through 31, the short form can be used in most cases.

The long form allows use of a more comprehensive set of terminator characters. Any mask equal to or greater than 1 byte is acceptable. For example, a mask size of 16 bytes allows all 7-bit ASCII characters to be used as terminators; a mask size of 32 bytes allows all 8-bit characters to be used as terminators for 8-bit terminals.

If the terminator mask is all zeros, there are no specified terminators. The read operation ends when the specified number of bytes (characters) have been transferred to the input buffer.

Certain control keys will not act as terminators unless IO$M_NOFILTR is specified or the line has the TT2$M_PASTHRU characteristic (see “Control Characters and Special Keys”).

Figure 5-3 Short and Long Forms of Terminator Mask Quadwords

Itemlist read operations provide expanded software features to read QIO requests. The operating system provides the following combination of function code and modifier:

No other function modifiers can be specified in an itemlist read request.

	NOTE: Itemlist read features supported by the terminal driver are not supported by all DECnet terminal emulators.

The itemlist read function code and modifier combination takes the following device- or function-dependent arguments:

P4 is not meaningful for itemlist read operations. P5 points to a series of item descriptors. Figure 5-4 shows the format for these descriptors. You cannot repeat the same item code in the same item list.

Figure 5-4 Itemlist Read Descriptor

Table 5-7 lists the item codes that can be specified in the first longword of the item descriptors.

When using the read verify function, the terminal driver performs input validation based on character attributes. (Read verification bypasses the optionally specified termination mask (TRM$_TERM).) Validation is performed one character at a time as data is entered. Invalid characters are not echoed, and cause the read operation to complete. It is then up to the application program to handle the error appropriately.

The initial string describes the initial contents of the input field. This string may consist of data and marker characters. The clear character is displayed on the screen for each occurrence of the fill character in the initial string buffer.

The picture string is a string of bytes where each byte corresponds to one character of the field being entered. Each byte specifies a mask of legal character types for that character position. If the byte is left as zero, then that position is a marker character, and the character from the initial string is echoed for that position.

For left-justified fields, the prompt data is output to the terminal, followed by an optional number (TRM$_INIOFFSET) of initial string characters. Leading marker characters are always output following the prompt, leaving the cursor at the leftmost data position. As each character is entered, it is validated and then echoed, advancing the cursor position. Additional marker characters are skipped as they are encountered. If an input character fails the validation, the read operation is completed with the invalid character as the terminator.

For right-justified fields, the prompt is output and is followed by the initial string. (In general, TRM$_INIOFFSET is set to the length of TRM$_INISTRNG for right-justified fields.) The cursor position remains one position to the right of the initial string. For proper operation, right-justified fields cannot have mixed picture definitions. After each character is input, the entire prompt and input fields are output. Therefore, the prompt should include a cursor positioning escape sequence.

The definition of full field is different for left- and right-justified read operations. For left-justified fields, full field is detected when the character corresponding to the last nonmarker position in the picture string has been entered. For right-justified fields, full field is detected when a character other than the fill character is shifted into the leftmost, nonmarker position in the field.

If the modifier TRM$M_TM_AUTO_TAB is set in TRM$_MODIFIERS, then detection of a full field terminates the read operation. In the event of autotab termination, the terminator character in the IOSB is null. If the autotab option is not selected, then termination occurs when one more character is typed to a full field. Applications can detect this condition when the terminating character index is one character beyond the end of the field. The extra character is reported as the terminator. In a left-justified field, the IOSB index to the terminator is zero-based; in a right-justified field, this index is one-based.

If a read verify function is interrupted by an asynchronous write operation, the read verify is completed with status SS$_OPINCOMPL.

No line editing functions other than the delete character function are supported for read verify.

Five function modifiers can be specified with IO$_WRITEVBLK, IO$_WRITELBLK, and IO$_WRITEPBLK. Table 5-8 lists these function modifiers. All write function modifiers are supported for LAT devices.

The P4 argument is a longword that specifies carriage control. Carriage control determines the next printing position on the terminal. P4 is ignored in a write physical block operation. Figure 5-5 shows the P4 longword format.

Figure 5-5 P4 Carriage Control Specifier

Only bytes 0, 2, and 3 in the longword are used. Byte 1 is ignored. If the low-order byte (byte 0) is not 0, the contents of the longword are interpreted as a FORTRAN carriage control specifier. Table 5-9 lists the possible byte 0 values (in hexadecimal) and their meanings.

If the low-order byte (byte 0) is 0, bytes 2 and 3 of the P4 longword are interpreted as the prefix and postfix carriage control specifiers. The prefix (byte 2) specifies the carriage control before the buffer contents are printed. The postfix (byte 3) specifies the carriage control after the buffer contents are printed. The sequence is as follows:

The prefix and postfix bytes, although interpreted separately, use the same encoding scheme. Table 5-10 shows this encoding scheme in hexadecimal.

With several exceptions, Figure 5-6 shows the prefix and postfix hexadecimal coding that produces the carriage control functions listed in Table 5-9. Prefix and postfix coding provides an alternative way to achieve these controls.

In the first example in Figure 5-6, the prefix/postfix hexadecimal coding for a single-space carriage control (carriage-return/line-feed combination, print buffer contents, return) is obtained by placing the value 1 in the second (prefix) byte and the sum of the bit 7 value (80) and the return value (D) in the third postfix byte.

 80  (bit 7 = 1)
+ D  (return)
—-
 8D  (postfix = return)

Figure 5-6 Write Function Carriage Control (Prefix and Postfix Coding)

The hangup function disconnects a terminal that is on a dialup line. (Dialup lines are described in “Set Mode”.) The following combinations of function code and modifier are provided:

The hangup function modifier takes no arguments. SS$_NORMAL is returned in the I/O status block.

	NOTE: For remote terminals, the hangup function breaks the network connection to the local system, ending the remote terminal session.

Both set mode functions can take the enable Ctrl/C AST and enable Ctrl/Y AST function modifiers. These function modifiers request the terminal driver to queue an AST for the requesting process when you press Ctrl/C or Ctrl/Y. The following combinations of function code and modifier are provided:

These function code modifier pairs take the following device- or function-dependent arguments:

If the respective enabling is in effect, pressing Ctrl/C or Ctrl/Y gains the attention of the enabling process (see Table 5-1).

Enable Ctrl/C and Ctrl/Y AST are one-time enabling function modifiers. After the AST occurs, it must be explicitly reenabled by one of the two function code combinations before an AST can occur again. This function code is also used to disable the AST. The function is subject to AST quotas.

You can have more than one Ctrl/C or Ctrl/Y enabled; pressing Ctrl/C, for example, results in the delivery of all Ctrl/C ASTs. ASTs are queued and delivered to the user process on a first-in/first-out basis for each access mode. However, ASTs are processed in the reverse order of the Ctrl/C AST or Ctrl/Y AST requests that have been issued to the terminal driver (on a last-in/first-out basis).

If no enable Ctrl/C AST is present, the holder of an enable Ctrl/Y AST receives an AST when Ctrl/C is pressed; carriage-return/line-feed combination, Ctrl/Y, and Return are echoed.

Figure 5-9 shows the relationship of Ctrl/C and Ctrl/Y with the out-of-band function. If Ctrl/C or Ctrl/Y is an enabled out-of-band character, any out-of-band ASTs specified for this character are delivered. If IO$M_INCLUDE function modifier is included in the out-of-band AST request for this character, an enabled Ctrl/C or Ctrl/Y AST is also delivered.

Enable Ctrl/C AST requests are flushed by the Cancel I/O on the Channel ($CANCEL) system service. Enable Ctrl/Y AST requests are flushed by the Deassign I/O Channel ($DASSGN) system service.

Ctrl/Y is normally used to gain the attention of the command interpreter and to input special commands such as DEBUG, STOP, and CONTINUE. Programs that are run from a command interpreter should not enable Ctrl/Y. Because ASTs are delivered on a first-in/first-out basis, the command interpreter's AST routine gets control first, and might not allow the program's AST to be delivered at all. Programs that require the use of Ctrl/Y should use the LIB$DISABLE_CTRL RTL routine to disable DCL recognition of Ctrl/Y.

See Example 5-4 for a programming example that demonstrates Ctrl/Y and Ctrl/C handling under OpenVMS.

“Control Characters and Special Keys” describes other effects of Ctrl/C and Ctrl/Y.

The set modem function modifier is used in maintenance operations to allow a process to activate and deactivate modem control signals. Both set mode and set characteristics functions can take the set modem function modifier. The following combinations of function code and modifier are provided:

	NOTE: For LAT devices, the set modem field for maintenance operations of the IO$M_SET_MODEM!IO$M_MAINT function modifier is unsupported and may return unpredictable results.

These function code modifier pairs take the following device- or function-dependent argument:

Figure 5-8 shows the format of this block.

The modem on and modem off fields, in combination or separately, can specify one or more of the following values:

The $TTDEF macro defines the values for these values. These values can only be specified if the terminal characteristic TT$M_MODEM is not set. Otherwise, an error (SS$_ABORT) occurs.

	NOTE: The set modem function is not supported for remote terminals. The status SS$_DEVREQERR is returned in the I/O status block. Because the DMF32 does not provide the secondary transmitted data signal (Sec Txd), the driver sets the secondary request to send the signal. Users should connect a jumper cable between pins 14 and 19 on the DMF32.

The loopback function modifier is used in maintenance operations to place the terminal line in a hardware loopback mode. Data transmitted to a line in this mode is returned as receive data. If the controller does not support loopback mode or the terminal line has the TT$M_MODEM characteristic set, an error status (SS$_ABORT) is returned. Both set mode functions can take the loopback function modifier.

	NOTE: The loopback function is not supported for remote terminals. The status SS$_DEVREQERR is returned in the I/O status block.

The following combinations of function code and modifier are provided:

Data transmitted in the loopback mode should only be written in records less than or equal to the size of the type-ahead buffer (see “Type-Ahead Feature”). Programs that use the loopback function modifier should incorporate a 1-second delay to allow the controller to enable the loopback mode after the request is posted. Write requests should also include the IO$M_NOFORMAT function modifier to prevent terminal driver from formatting input or output data.

The operating system provides another function modifier to reset a terminal line previously placed in loopback mode. The following combinations of function code and modifier are provided:

Programs that use the unloop function modifier should incorporate a 1-second delay to allow the controller to reset the loopback mode after the request is posted.

	NOTE: IO$M_LOOP and IO$M_UNLOOP are not supported for LAT devices.

The enable out-of-band AST function modifier requests that the terminal driver queue an AST for the requesting process when you enter any one of 32 control characters. The following combinations of function code and modifier are provided:

These function code modifier pairs take the following device- or function-dependent arguments:

The IO$_SETMODE!IO$M_OUTBAND function can optionally take the following function modifiers:

If an out-of-band AST is in effect, pressing any control character specified in the P2 mask gains the attention of the enabling process. Figure 5-9 shows the relationship of the out-of-band function with some of the control characters.

You can have only one out-of-band AST enabled per channel.

Out-of-band ASTs are repeating ASTs; they continue to be delivered until specifically disabled. Out-of-band AST enables are flushed by the Cancel I/O on Channel ($CANCEL) system service.

Figure 5-9 Relationship of Out-of-Band Function with Control Characters

The broadcast function modifier allows you to turn on or turn off selected broadcast requester identifiers (IDs). The following combination of function code and modifier is provided:

This function code modifier pair takes the following device- or function-dependent arguments:

The first longword of P1 is reserved for use by HP facilities, as shown in Table 5-11. The symbols are defined in the system macro library ($BRKDEF). The second longword is for customer use to specify selected bits. If any bit is set in the P1 buffer, that particular requester ID is turned off for broadcast.

QIO functions can be used to create the following LAT port types:

The operating system provides the following combinations of function code and modifier:

The LAT SETMODE $QIO function (IO$_TTY_PORT!IO$M_LT_SETMODE) is used to create, delete, and modify LAT nodes, services, ports, and links.

Creation, deletion, or modification of any entity requires the OPER privilege.

The LAT SETMODE $QIO function accepts four arguments: P1, P2, P3, and P4. P1 is the address of an item list; P2 is the length of this item list.

P3 specifies the type of entity to which the SETMODE operation applies. The entity type can be one of five types:

The value for the entity type occupies the low-order 16 bits (bits 0--15) of the P3 parameter. For all four entity types, bits 16--19 are used as a status field to indicate the expected current status of the entity. These bits are used to decide whether the entity needs to be created before its characteristics are set. The possible values for this field are:

P4 may contain the address of an entity name string descriptor. If this parameter is omitted (contains a 0 or the address of a descriptor that points to an empty buffer), a default may be used in some cases. The defaults for each entity type are as follows:

SETMODE can return the following status codes:

SETMODE Item Codes

Each item in the itemlist consists of a one-word (16-bit) item code, followed by a value associated with the item.

Item codes in which the bit named LAT$V_STRING is zero take a longword value. The associated value is contained in the longword immediately following the item code in the itemlist. Item codes in which this bit is 1 take a counted string for their value. The byte immediately following the item code contains a byte count, which describes the length of the string that immediately follows it.

If you set bit LAT$V_CLEAR in the item code to 1, the current value associated with the item code is cleared or set to its default value. In this case, the actual value specified in the itemlist is ignored, although the byte count field skips to the next item in the itemlist.

Figure 5-10 shows an example of a SETMODE itemlist.

Figure 5-10 Example SETMODE Itemlist

This SETMODE itemlist is the P1 parameter for a $QIO SETMODE function on the local node. P4 is omitted, and P3 is #LAT$C_ENT_NODE!$C_ENTS_OLD@16>. P2 is the length of the itemlist (52). A $QIO SETMODE function for this itemlist would perform the following operations:

For each entity type, only a subset of item codes may be set. Table 5-12 lists the item codes that may be set for the LAT$C_ENT_NODE entity type.

Table 5-13 lists the item codes that may be set for the LAT$C_ENT_SERVICE entity type.

Table 5-14 lists the item codes that may be set for the LAT$C_ENT_LINK entity type.

Table 5-15 lists the item codes that may be set for the LAT$C_ENT_PORT entity type.

The LAT SENSEMODE $QIO function (IO$_TTY_PORT!IO$M_LT_SENSEMODE) is used to obtain information about LAT nodes, services, ports, and links.

The LAT SENSEMODE $QIO function accepts four arguments: P1, P2, P3, and P4. P1 is the address of a buffer into which information about the desired entity is returned. The information is returned in the form of an item list. Unlike system services such as $GETDVI or $GETJPI, you do not select which items of information are returned. P2 is the length of the buffer specified in P1, in bytes. The number of bytes of information returned in the P1 buffer is returned in IOSB+2.

P3 specifies the type of entity to which the SENSEMODE operation applies. The entity type can be one of five types:

The value for the entity type occupies the low-order 16 bits (bits 0--15) of the P3 parameter. Bits 16--23 are used as a flag field. Two bits are currently defined within this field: LAT$V_SENSE_NEXT and LAT$V_SENSE_FULL. If the LAT$V_SENSE_NEXT bit is 0, information about the current entity described by the P3 and P4 parameters is returned to the user; if this bit is 1, information about the next entity that logically follows the one described by P4 is returned. If LAT$V_SENSE_FULL is 0, only those item codes marked SUMMARY in the following tables are returned; if this bit is 1, all item codes that describe the entity specified by the P3 and P4 parameters are returned.

P4 may contain the address of an entity name string descriptor. If this parameter is omitted (contains a zero or the address of a descriptor that points to an empty string) and the LAT$V_SENSE_NEXT bit is set, information about the first entity that matches the entity type supplied by P3 is returned.

If P4 is omitted and the LAT$V_SENSE_NEXT bit is 0, a default entity name may be used in some cases. The defaults for each entity type are as follows:

SENSEMODE can return the following failure return codes:

5.3.4.4.1 SENSEMODE Item Codes

Each item in the itemlist starts with a one-word (16-bit) item code that describes the type of information contained in the item. The item code is followed by a value associated with the item.

Item codes in which the bit named LAT$V_STRING is 0 take a longword value. The associated value is contained in the longword immediately following the item code in the itemlist. Item codes in which this bit is 1 take a counted string for their value. The byte immediately following the item code contains a byte count, which describes the length of the string that immediately follows it.

Table 5-16 lists the item codes that are returned for the LAT$C_ENT_NODE entity type. Item codes noted as LOCAL are returned only if the information being returned is for the local node. Item codes noted as REMOTE are returned only if the information being returned is for a remote node. Item codes noted as BOTH are returned for both types of nodes.

Table 5-16 LAT$C_ENT_NODE Item Codes

Item Code	Meaning
LAT$_ITM_NODE_NAME (BOTH, SUMMARY)	LAT node name for the node.
LAT$_ITM_IDENTIFICATION (BOTH, SUMMARY)	Node identification string.
LAT$_ITM_NODE_TYPE (BOTH, SUMMARY)	Type of node. Possible values are:
	LAT$C_NT_LOCAL	Node is local node.
	LAT$C_NT_REMOTE	Node is remote node.
LAT$_ITM_STATE (LOCAL,SUMMARY)	Operating state of the LAT protocol. Possible values are:
	LAT$C_ON	New connections are allowed and the LAT protocol is running.
	LAT$C_OFF	New connections are not allowed. The LAT protocol is not running.
		No new connections are allowed. Currently active connections are still maintained. The LAT protocol remains running only until the last active session is disconnected, at which time the node is placed in the OFF state.
LAT$_ITM_NODE_STATUS (REMOTE, SUMMARY)	Current status of remote node. This item code is present only if a LAT virtual circuit does not currently exist between the local node and this remote node. Possible values are:
	LAT$C_REACHABLE	Remote node is reachable.
	LAT$C_UNREACHABLE	Remote node is unreachable.
	LAT$C_UNKNOWN	Remote node status is unknown.
LAT$_ITM_CONNECTED_COUNT (REMOTE, SUMMARY)	Number of LAT sessions from the local node to this remote node. This item code replaces the LAT$_ITM_NODE_STATUS item code for remote nodes to which a LAT virtual circuit currently exists.
LAT$_ITM_SERVICE_GROUPS (BOTH)	A bit mask of LAT group codes that are serviced by the node.
LAT$_ITM_PROTOCOL_VERSION (BOTH)	LAT protocol version string.
LAT$_ITM_DATALINK_ ADDRESS (REMOTE)	LAN address used by the node.
LAT$_ITM_NODE_LIMIT	Maximum number of nodes in LAT database. The default is 0, where the maximum is determined by system resources.
LAT$_ITM_RETRANSMIT_ LIMIT	LAT retransmit limit. Possible values are 4 to 120 retransmissions. The default is 8 retransmissions.
LAT$_ITM_MAXIMUM_UNITS (LOCAL)	Maximum LTA unit number.
LAT$_ITM_SERVER_MODE (LOCAL)	Controls whether the node allows the use of the MASTER side of the LAT protocol for outbound connections. Possible values are:
	LAT$C_DISABLED	Server mode disabled (this is the default).
	LAT$C_ENABLED	Server mode enabled.
LAT$_ITM_SERVICE_RESPONDER (LOCAL)	Indicates whether the node is to respond to service inquiries originating from a remote system. These inquiries are not necessarily directed at services being offered by the node. See the HP OpenVMS System Management Utilities Reference Manual for more information on this feature. Possible values are:
	LAT$C_DISABLED	Service responder disabled (this is the default).
	LAT$C_ENABLED	Service responder enabled.
LAT$_ITM_OUTGOING_SES_LIMIT (LOCAL)	Maximum number of outgoing LAT sessions. A value of 0, which is the default, indicates that the limit is determined by system resources.
LAT$_ITM_INCOMING_SES_LIMIT (LOCAL)	Maximum number of interactive LAT sessions. A value of 0, which is the default, indicates that the limit is determined by system resources.
LAT$_ITM_USER_GROUPS (LOCAL)	Bit mask of LAT group codes to be used when attempting outbound connections using the MASTER side of the LAT protocol.
LAT$_ITM_CIRCUIT_TIMER (BOTH)	Circuit timer value in milliseconds. Possible values are 10 to 1000 milliseconds. The default is 80 milliseconds.
LAT$_ITM_CPU_RATING (LOCAL)	CPU rating.
LAT$_ITM_KEEPALIVE_TIMER (LOCAL)	Keepalive timer value in seconds. Possible values are 10 to 255 seconds. The default is 20 seconds.
LAT$_ITM_MULTICAST_TIMER (BOTH)	Multicast timer value in seconds. Possible values are 10 to 180 seconds. The default is 20 seconds.
LAT$_ITM_CONNECTIONS (BOTH)	Indicates whether inbound connections (interactive sessions) can be accepted. Possible values are:
	LAT$C_DISABLED	Inbound connections disabled.
	LAT$C_ENABLED	Inbound connections enabled (this is the default).
LAT$C_ITM_LARGE_BUFFERS	Indicates in Boolean logic whether the LAT software is using large packet support by default.
LAT$C_ITM_ ANNOUNCEMENTS	Indicates in Boolean logic whether the LAT software is transmitting LAT service advertisement messages.

 

Node service information is presented as a list of node service subblocks, with each subblock containing information about one particular service offered by the node. The subblock item code LAT$_ITM_NODE_SVC_BLOCK has the LAT$V_STRING bit set to 1, and the string length byte actually contains the length of the entire subblock. Each subblock itself is an itemlist and consists of the item codes listed in Table 5-17.

Table 5-17 Node Service Subblock Item Codes

Item Code	Meaning
LAT$_ITM_SERVICE_NAME (BOTH)	Name of a LAT service offered by the node.
LAT$_ITM_SERVICE_STATUS (BOTH)	Status of the service. Possible values are:
	LAT$C_AVAILABLE	Service available.
	LAT$C_UNAVAILABLE	Service unavailable.
LAT$_ITM_SERVICE_TYPE (LOCAL)	Type of service. Possible values are:
	LAT$C_ST_GENERAL	Creates a general timesharing service.
	LAT$C_ST_APPLICATION	Creates a special application service that must then be associated with ports dedicated to accepting connections to this service (dedicated ports).
LAT$_ITM_RATING (BOTH)	LAT service rating associated with the service.
LAT$_ITM_RATING_TYPE (LOCAL)	Type of LAT rating calculation being done by this node. Possible values are:
	LAT$C_STATIC	Static rating calculation
	LAT$C_DYNAMIC	Dynamic rating calculation
LAT$_ITM_IDENTIFICATION (BOTH)	Identification string associated with the service.

 

On Alpha and Integrity server systems, port counters information is presented as a counters subblock. The subblock item code LAT$_ITM_COUNTERS has the LAT$V_STRING bit set to 1, and the string length byte actually contains the length of the entire subblock. The subblock itself is an itemlist and consists of the item codes listed in Table 5-18.

Table 5-18 Node Counters Item Codes

Item Codes	Meaning
LAT$_ITM_CTPRT_LCL	Indicates number of local accesses to port.
LAT$_ITM_CTPRT_SLCA	Indicates number of solicitations accepted.
LAT$_ITM_CTPRT_SLCR	Indicates number of solicitations rejected.
LAT$_ITM_CTPRT_ISOLA	Indicates number of incoming solicitations accepted.
LAT$_ITM_CTPRT_ISOLR	Indicates number of incoming solicitations rejected.
LAT$_ITM_CTPRT_FRAMERR	Indicates number of framing errors for named port. Returned in port counter subblock.
LAT$_ITM_CTPRT_PARERR	Indicates number of parity errors for named port. Returned in port counter subblock.
LAT$_ITM_CTPRT_OVERRUN	Indicates number of data overruns for named port. Returned in port counter subblock.
LAT$_ITM_PASSWORD_FAILURES	Indicates password failures.

 

Node counters information is presented as a counters subblock. The subblock item code LAT$_ITM_COUNTERS has the LAT$V_STRING bit set to 1, and the string length byte actually contains the length of the entire subblock. The subblock itself is an itemlist and consists of the item codes listed in Table 5-19.

Table 5-19 Node Counters Item Codes

Item Codes	Meaning
LAT$_ITM_CTNOD_SSZ (BOTH)	Seconds since zeroed
LAT$_ITM_CTNOD_MSGR (BOTH)	Messages received
LAT$_ITM_CTNOD_MSGT (BOTH)	Messages transmitted
LAT$_ITM_CTNOD_SLTR (BOTH)	Slots received
LAT$_ITM_CTNOD_SLTT (BOTH)	Slots transmitted
LAT$_ITM_CTNOD_BYTR (BOTH)	Bytes received
LAT$_ITM_CTNOD_MNA (BOTH)	Multiple node addresses
LAT$_ITM_CTNOD_DUP (BOTH)	Duplicates received
LAT$_ITM_CTNOD_MRT (BOTH)	Messages retransmitted
LAT$_ITM_CTNOD_ILM (BOTH)	Illegal messages received
LAT$_ITM_CTNOD_ILS (BOTH)	Illegal slots received
LAT$_ITM_CTNOD_SLCA (BOTH)	Solicitations accepted
LAT$_ITM_CTNOD_SLCR (BOTH)	Solicitations rejected
LAT$_ITM_CTNOD_TER (LOCAL)	Transmit errors
LAT$_ITM_CTNOD_RES (LOCAL)	Resource errors
LAT$_ITM_CTNOD_NTB (LOCAL)	No transmit buffer
LAT$_ITM_CTNOD_TMO (LOCAL)	Virtual circuit timeout
LAT$_ITM_CTNOD_DOB (LOCAL)	Discarded output bytes
LAT$_ITM_CTNOD_LSTER (LOCAL)	Last transmit error
LAT$_ITM_CTNOD_MCBXMT (LOCAL)	Number of multicast bytes transmitted
LAT$_ITM_CTNOD_MCBRCV (LOCAL)	Number of multicast bytes received
LAT$_ITM_CTNOD_MCMXMT (LOCAL)	Number of multicast messages transmitted
LAT$_ITM_CTNOD_MCMRCV (LOCAL)	Number of multicast messages received
LAT$_ITM_CTNOD_SOLFAIL (LOCAL)	Number of solicitation failures
LAT$_ITM_CTNOD_ATLOS (LOCAL)	Number of times attention slot data was lost
LAT$_ITM_CTNOD_DATLOS (LOCAL)	Number of times user data was lost
LAT$_ITM_CTNOD_NOREJ (LOCAL)	Number of times a reject slot could not be sent
LAT$_ITM_CTNOD_LOSCT (LOCAL)	Number of times remote node counters were lost
LAT$_ITM_CTNOD_LOSSAM (LOCAL)	Number of service announcement messages lost
LAT$_ITM_CTNOD_NOSAM (LOCAL)	Number of times a service announcement message could not be sent
LAT$_ITM_CTNOD_NOSTS (LOCAL)	Number of times node status was lost
LAT$_ITM_CTNOD_NOXMT (LOCAL)	Number of times no link was available for a transmit
LAT$_ITM_CTNOD_CTLERR (LOCAL)	Number of controller errors
LAT$_ITM_CTNOD_CERRCOD (LOCAL)	Lost controller error
LAT$_ITM_CTNOD_ISOLA (LOCAL)	Number of incoming solicitations accepted
LAT$_ITM_CTNOD_ISOLR (LOCAL)	Number of incoming solicitations rejected
LAT$_ITM_CTNOD_PROTO (LOCAL)	Protocol error count
LAT$_ITM_CTNOD_XSTR (REMOTE)[1]	Indicates that the node attempted to start up too many LAT sessions for a specific virtual circuit
[1] Alpha and Integrity servers specific.

 

Several protocol errors are also included in a separate subblock. The protocol errors item code is LAT$_ITM_PROTOCOL_ERRORS and has LAT$V_STRING set (the size of the subblock is contained in the first byte following the item code). The item codes and the events they represent are listed in Table 5-20.

Table 5-20 Protocol Error Item Codes

Item Codes	Meaning
LAT$_ITM_CTPRO_IVM (LOCAL)	Invalid message type received.
LAT$_ITM_CTPRO_ISM (LOCAL)	Invalid start message received.
LAT$_ITM_CTPRO_IVS (LOCAL)	Invalid sequence number received.
LAT$_ITM_CTPRO_NIZ (LOCAL)	Zero-node index received.
LAT$_ITM_CTPRO_ICI (LOCAL)	Node circuit index out of range.
LAT$_ITM_CTPRO_CSI (LOCAL)	Node circuit sequence invalid.
LAT$_ITM_CTPRO_NLV (LOCAL)	Node circuit index no longer valid.
LAT$_ITM_CTPRO_HALT (LOCAL)	Circuit was forced to halt.
LAT$_ITM_CTPRO_MIZ (LOCAL)	Invalid master slot index.
LAT$_ITM_CTPRO_SIZ (LOCAL)	Invalid slave slot index.
LAT$_ITM_CTPRO_CRED (LOCAL)	Invalid credit field.
LAT$_ITM_CTPRO_RCSM (LOCAL)	Repeat creation of slot by master.
LAT$_ITM_CTPRO_RDSM (LOCAL)	Repeat disconnection of slot by master.
LAT$_ITM_CTPRO_INVCLASS (LOCAL)	Indicates the number of times a LAT message was received with an invalid service class specified in that message (local node only).
LAT$_ITM_CTPRO_EXCSTART (LOCAL)[1]	Indicates that a remote node attempted to start up too many LAT sessions. When a virtual circuit is started between two LAT nodes, the maximum number of sessions on that virtual circuit is negotiated. If the master node attempts to create more sessions than the maximum number of sessions on a virtual circuit, then the operating system rejects the excess connections and increments this counter.
[1] Alpha and Integrity servers specific.

 

Table 5-21 lists the item codes that are returned for the LAT$C_ENT_SERVICE entity type. As in Table 5-16, item codes noted as LOCAL are returned only if the information being returned is for a locally offered service. Item codes noted as REMOTE are returned only if the information being returned is for a service offered by a remote node. Item codes noted as BOTH are returned for both types of services.

Table 5-21 LAT$C_ENT_SERVICE Item Codes

Item Code	Meaning
LAT$_ITM_SERVICE_NAME (BOTH, SUMMARY)	Service name.
LAT$_ITM_SERVICE_STATUS (BOTH, SUMMARY)	Status of the specified service. Possible values are:
	LAT$C_AVAILABLE	Service available.
	LAT$C_UNAVAILABLE	Service unavailable.
LAT$_ITM_SERVICE_TYPE (LOCAL,SUMMARY)	Type of service. Possible values are:
	LAT$C_ST_GENERAL	General timesharing service.
	LAT$C_ST_APPLICATION	Special application service associated with ports dedicated to accepting connections to this service.
LAT$_ITM_IDENTIFICATION (BOTH, SUMMARY)	Service identification string, as advertised by the highest rated node that currently offers the service.

 

Service node information is presented as a list of service node subblocks, with each subblock containing information about one particular node that offers the service. The subblock item code LAT$_ITM_SVC_NODE_BLOCK has the LAT$V_STRING bit set to 1, and the string length byte actually contains the length of the entire subblock. Each subblock itself is an itemlist and consists of the item codes listed in Table 5-22.

Table 5-22 Service Node Subblock Item Codes

Item Code	Meaning
LAT$C_ITM_NODE_NAME (BOTH)	Name of a LAT node that offers the selected service.
LAT$_ITM_STATE (LOCAL)	Current state of the LAT protocol on the local node. Possible values are:
	LAT$C_ON	New connections are allowed, and the LAT protocol is running.
	LAT$C_OFF	New connections are not allowed, and any current connections are abnormally terminated. The LAT protocol is not running.
	LAT$C_SHUT	No new connections are allowed. Currently active connections are still maintained. The LAT protocol remains running only until the last active sessions is disconnected, at which time the node is placed in the OFF state.
LAT$_ITM_NODE_STATUS (REMOTE)	Current status of the remote node. This item code is present only if a LAT virtual circuit does not currently exist to the remote node. Possible values are:
	LAT$C_REACHABLE	Remote node is reachable.
	LAT$C_UNREACHABLE	Remote node is unreachable.
	LAT$C_UNKNOWN	Remote node status is unknown.
LAT$_ITM_CONNECTED_COUNT (REMOTE)	Number of LAT sessions from the local node to this remote node. This item code replaces the LAT$_ITM_NODE_STATUS item code for remote nodes to which a LAT virtual circuit currently exists.
LAT$_ITM_RATING (BOTH)	LAT service rating associated with the service.
LAT$_ITM_RATING_TYPE (LOCAL)	Type of LAT rating calculation being done by this node. Possible values are LAT$C_STATIC and LAT$C_DYNAMIC.
LAT$_ITM_IDENTIFICATION (BOTH)	Identification string associated with the service.

 

Service counters information is presented as a counters subblock. The subblock item code LAT$_ITM_COUNTERS has the LAT$V_STRING bit set, and the string length byte actually contains the length of the entire subblock. Each subblock itself is an itemlist and consists of the item codes listed in Table 5-23.

Table 5-23 Service Counters Subblock Item Codes

Item Codes	Meaning
LAT$_ITM_CTSRV_SSZ (BOTH)	Seconds since zeroed.
LAT$_ITM_CTSRV_MCNA (BOTH)	Outgoing connections attempted (the number of times the local node has attempted to connect to the service offered on a remote node). Outgoing connections completed (the number of times the local node successfully connected to the service offered on a remote node).
LAT$_ITM_CTSRV_MCNC (BOTH)
LAT$_ITM_CTSRV_SCNA (BOTH)	Incoming connections accepted (the number of times the local node has accepted a connection request from a remote node to the locally offered service).
LAT$_ITM_CTSRV_SCNR (BOTH)	Incoming connections rejected (the number of times the local node rejected a connection request from a remote node to the locally offered service).
LAT$_ITM_DED_PORT_BLOCK (LOCAL)	If the selected service is an application service offered by the local node, a list of one or more port subblocks is included in the itemlist. These subblocks describe the dedicated port or ports associated with this application service, with each subblock describing one particular port. The subblock item code LAT$_ITM_DED_PORT_BLOCK has the LAT$V_STRING bit set, and the string length byte actually contains the length of the entire subblock. Each subblock itself is an itemlist and currently consists only of the following item code:
	LAT$_ITM_PORT_NAME (LOCAL)	Name of the dedicated port.
LAT$_ITM_PASSWORD_ FAILURE	Indicates password failures.

 

Table 5-24 lists the item codes that are returned for the LAT$C_ENT_LINK entity type.

Table 5-24 LAT$C_ENT_LINK Item Codes

Item Codes	Meaning
LAT$_ITM_LINK_NAME (SUMMARY)	Link name (such as LAT$LINK).
LAT$_ITM_STATE (SUMMARY)	State of the link. Possible values are:
	LAT$C_ON	New connections are allowed, and the LAT protocol is running.
	LAT$C_OFF	New connections are not allowed, and any current connections are abnormally terminated. The LAT protocol is not running.
	LAT$C_SHUT	No new connections are allowed. Currently active connections are still maintained. The LAT protocol remains running only until the last active session is disconnected, at which time the node is placed in the OFF state.
LAT$_ITM_DEVICE_NAME (SUMMARY)	The name of the LAN device used for the link.
LAT$_ITM_DATALINK_ADDRESS	The LAN device's current physical address for the link.
LAT$_ITM_DECNET_ADDRESS	Indicates whether the link attempts to use the default DECnet LAN address when starting the data link controller (enabling the LAT protocol). Possible values are:
	LAT$C_DISABLED	DECnet LAN address use disabled.
	LAT$C_ENABLED	DECnet LAN address use enabled (this is the default.

 

Link counters information is presented as a counters subblock. The subblock item code LAT$_ITM_COUNTERS has the LAT$V_STRING bit set, and the string length byte actually contains the length of the entire subblock. Because the link counters are independent of the protocol type, they include not only LAT messages and events, but also all other protocol messages and events (that is, DECnet) associated with the same LAN device. The counters are actually maintained by the LAN device driver and are identified within the subblock by the nonprotocol-specific item codes listed in Table 5-25.

Table 5-25 Link Counters Item Codes

Item Codes	Meaning
NMA$C_CTLIN_ZER	Seconds since zeroed
NMA$C_CTLIN_DBR	Messages received
NMA$C_CTLIN_DBS	Messages transmitted
NMA$C_CTLIN_MBL	Multicast messages received
NMA$C_CTLIN_MBS	Multicast messages transmitted
NMA$C_CTLIN_BRC	Bytes received
NMA$C_CTLIN_BSN	Bytes transmitted
NMA$C_CTLIN_MBY	Multicast bytes received
NMA$C_CTLIN_MSN	Multicast bytes transmitted
NMA$C_CTLIN_RFL	Receive errors
NMA$C_CTLIN_SFL	Transmit errors
NMA$C_CTLIN_OVR	Data overrun
NMA$C_CTLIN_UBU	User buffer unavailable
NMA$C_CTLIN_SBU	System buffer unavailable
NMA$C_CTLIN_LBE	Local buffer errors
NMA$C_CTLIN_BS1	Messages sent, single collisions
NMA$C_CTLIN_BSM	Messages sent, multiple collisions
NMA$C_CTLIN_BID	Messages sent, initially deferred
NMA$C_CTLIN_CDC	Transmit collision detection check failure

 

Table 5-26 lists additional link counter item codes of the LINK entity.

Table 5-26 Additional Link Counters Item Codes

Item Codes	Meaning
LAT$_ITM_CTLAT_RMSG	Count of LAT messages received through link
LAT$_ITM_CTLAT_RBYT	Count of bytes for LAT received through link
LAT$_ITM_CTLAT_XMSG	Count of LAT messages transmitted through link
LAT$_ITM_CTLAT_XBYT	Count of bytes for LAT transmitted through link
LAT$_ITM_CTLAT_MUL_RMSG	Count of LAT multicast messages received through link
LAT$_ITM_CTLAT_MUL_RBYT	Count of multicast bytes for LAT received through link
LAT$_ITM_CTLAT_MUL_XMSG	Count of LAT multicast messages transmitted through link
LAT$_ITM_CTLAT_MUL_XBYT	Count of multicast bytes for LAT transmitted through link
LAT$_ITM_LAT_DEV_CTR_BLOCK	This block contains the LAT-specific counters for the specified link. Counters returned in this block are the ones defined above (with CTLAT in their name). These counters are LAT-specific for the link (device). They do not include counts from other protocols using the same adapter.

 

The counter item codes listed in Table 5-26 are used by LATCP in the display generated by the command:

$SHOW LINK /COUNTER

The display looks similar to the following: Link Name: LAT$LINK Device Name: _XQA1: Seconds Since Zeroed: 65535 Messages Received: 7080630 Messages Sent: 2135394 LAT Messages Received: 1484817 LAT Messages Sent: 2086167 Multicast Msgs Received: 5578139 Multicast Msgs Sent: 10775 LAT Multicast Msgs Received: 5093417 LAT Multicast Msgs Sent: 9142 Bytes Received: 678189475 Bytes Sent: 1312778402 LAT Bytes Received: 107809441 LAT Bytes Sent: 1278118808 Multicast Bytes Received: 602984574 Multicast Bytes Sent: 1696264 LAT Multicast Bytes Received: 565264261 LAT Multicast Bytes Sent: 1448342 System Buffer Unavailable: 1638401 User Buffer Unavailable: 1 Unrecognized Destination: 65537 Data Overrun: 1 Receive Errors: 7 Transmit Errors: 1 Receive Errors (bitmask = 001) - Transmit Errors (bitmask = 001) - Block Check Error: Yes Excessive Collisions: Yes Framing Error: No Carrier Check Failure: No Frame Too Long: No Short Circuit: No Frame Status Error: No Open Circuit: No Frame Length Error: No Frame Too Long: No Remote Failure To Defer: No Transmit Underrun: No Transmit Failure: No CSMACD Specific Counters ———————— Transmit CDC Failure: 1 Messages Transmitted - Single Collision: 5208 Multiple Collisions: 4732 Initially Deferred: 0

Table 5-27 lists the item codes that are returned for the LAT$C_ENT_PORT entity type.

Table 5-27 LAT$C_ENT_PORT Item Codes

Item Code		Meaning
LAT$_ITM_PORT_NAME_SUMMARY		Name of the port (such as _LTA15:).
LAT$_ITM_PORT_TYPE_SUMMARY		Type of port.
	Possible values are:
	LAT$_PT_FORWARD	Forward port used for outgoing LAT connections or for management functions.
	LAT$_PT_INTERACTIVE	Interactive port created as the result of an incoming LAT connection request.
	LAT$_PT_APPLICATION	Application port for solicited connections.
	LAT$_PT_DEDICATED	Dedicated port associated with a local service.
LAT$_ITM_QUEUED		Controls whether the solicited connection requests queued or nonqueued access.
	Possible values are:
	LAT$C_DISABLED	Queued access disabled.
	LAT$C_ENABLED	Queued access enabled (this is the default).
LAT$_ITM_SERVICE_CLASS		Indicates the class driver with which the device is communicating. This item code can be used only with an entity status of LAT$C_ENTS_NEW. Therefore, the service class must be specified when the device is created. An attempt to change the service class of an existing device returns SS$_BADPARAM.
	Possible values are:
	LAT$C_SERVCLASS_INTERACTIVE	Service class 1, TTDRIVER (this is the default).
	LAT$C_SERVCLASS_TESTSERVICE	Service class 2, TEST SERVICE.
	LAT$C_SERVCLASS_XTRANSPORT	Service class 3, X Protocol.
	LAT$C_SERVCLASS_FONT	Service class 4, X fonts.
LAT$_ITM_DISPLAY_NUMBER		Display number value for the device. This field has meaning for services classes 3 and 4 (X) only. It returns a value of 0 for all other service classes.
LAT$_ITM_DISCONNECT_REASON		Reason (if any) for the last disconnect on the port. If it is not a 0--19 LAT rejection code, it is a LAT message code. The 0--19 LAT rejection code meanings are listed in Table 5-31.
LAT$C_PT_STATE_DISCONNECTING[1]		Name of service to which this port is connected. For forward and application ports, this is the name of the remote service to which the port is connected (if any). For interactive and dedicated ports, this is the name of the local service that accepted the remote-initiated connection.
LAT$_ITM_CONNECTED_NODE_NAME[1]		Name of remote node to which this port is connected.
LAT$_ITM_CONNECTED_PORT_NAME[1]		Name of remote port to which this port is connected.
LAT$_ITM_CONNECTED_LINK_NAME[1]		Name of the link on which the LAT connection exists.
LAT$_ITM_TARGET_SERVICE_NAME[2]		Target service name for connection of forward or application ports. For dedicated ports, this item code specifies the local service with which the port is associated.
LAT$_ITM_TARGET_NODE_NAME[2]		Target node name for connection of forward or application ports.
LAT$_ITM_TARGET_PORT_NAME[2]		Target port name for connection of forward or application ports.
LAT$_ITM_NODE_QUEUE_POSITION[3]		Indicates current node queue position for connect request. Returned during SENSEMODE of port entity.
LAT$_ITM_SERVICE_QUEUE_POSITION[3]		Indicates current service queue position for connect request. Returned during SENSEMODE of port entity.
LAT$_ITM_PORT_STATE		Current port state.
	Possible values are:
	LAT$C_PT_STATE_INACTIVE	Port is inactive.
	LAT$C_PT_STATE_CONNECTING	Port connection in progress but not complete.
	LAT$C_PT_STATE_ACTIVE	Port has active LAT connection.
	LAT$C_PT_STATE_DISCONNECTING	Port LAT connection in process of terminating.
[1] Returned only when the LTA port has an active LAT connection. [2] Shows information about how the port is set up. May be returned even if there is no current LAT connection. [3] Alpha and Integrity servers specific.

 

On Alpha and Integrity server systems, the item codes for queue entries are listed in Table 5-28.

Table 5-28 LAT SENSEMODE Queue Entries

Item Code	Meaning
LAT$_ITM_QUEUED_ENTRY_ID (SUMMARY)	Indicates by string the queue entry ID name.
LAT$_ITM_NODE_QUEUE_POSITION (SUMMARY)	Indicates the current position of entry in node wide queue.
LAT$_ITM_SERVICE_QUEUE_POSITION (SUMMARY)	Indicates the current position of entry in service wide queue.
LAT$_ITM_NODE_NAME (SUMMARY)	Indicates where the remote node name queue entry came from.
LAT$_ITM_SERVICE_NAME (SUMMARY)	Indicates the target service name to which the queue entry is queued (if specified).
LAT$_ITM_PORT_NAME (SUMMARY)	Indicates the target port name to which the entry is queued (if specified).
LAT$_ITM_LINK_NAME	Returns the link name on which the queued request is active.
LAT$_ITM_DATALINK_ADDRESS	Returns the remote node that issued the request’s data link address.

 

An application port is used to connect to a remote device (typically a printer) on a terminal server or to a dedicated port on another LAT service node. The LAT port driver can only connect to a remote device if the device is currently not in use. Table 5-29 lists the conditions that can occur when an application program issues an IO$M_LT_CONNECT request for a connection to a remote device. After a request is queued on the terminal server (or dedicated port on another LAT service node), the QIO request is not completed until the connection is established, rejected, or times out.

Before the application port can be used, it must be mapped to a remote node name, and either the port name or the service name of the remote terminal server port. (These names must be defined locally on the terminal server.) The application port is mapped with the IO$M_LT_SETMODE modifier, specifying the following items in the P1 itemlist parameter:

The queued status of the connection can also be mapped to the port by specifying the LAT$_ITM_QUEUED item in the P1 itemlist parameter. Valid values for this item are:

Rather than the normal timesharing service offered by the operating system, application programs can make use of LAT application services that allow terminal server users (or users on systems with outgoing connections) to connect to a specialized application. To do this, the system manager must create LAT ports that are dedicated to a particular application service. (Alternatively, this LAT port creation can be done from a program using the QIOs discussed in previous sections, providing OPER privilege.) When the remote user makes the connection to the application service, the connection is directly to the application program that controls a LAT port (LTA device) associated with the service. In this case the prompt, Username:, is not received. HP recommends that you follow these steps to create an application service:

An example of the application service concept is a program that provides the time of day. For this example, the system manager includes the following lines in LAT$SYSTARTUP.COM (or enters them manually in the LATCP program):

CREATE SERVICE TIME/ID="At the tone, the time will be"/APPLICATION
CREATE PORT LTA99:/DEDICATED
SET PORT LTA99:/SERVICE=TIME

An application program then assigns a channel to device LTA99. When a terminal server user types CONNECT TIME, the user is connected to this application program, and the program prints out the time of day. The program then deassigns the channel, which disconnects the server user.

A system manager may associate more than one LAT port with the same service. In that case, the application program that offers the service should assign channels to all of the LTA devices created for that service.

An outbound LAT connection to a remote service node can be made using a forward port. The LAT port driver can connect to a remote service node only if outgoing connections are enabled on the local node. Outgoing connections can be enabled with LATCP or with a LAT SETMODE QIO to the local node. In addition, user group codes on the local node must match the service group codes of the service to which they are being connected. LATCP can list the services to which the local node can connect. (For additional information, see the HP OpenVMS System Management Utilities Reference Manual.) Before the forward port can be used to make an outbound LAT connection, it must be mapped to a service and optionally, a node and port. The forward port is mapped with the IO$M_LT_SETMODE modifier, specifying the following items in the P1 item list parameter:

A LAT SETMODE QIO on a forward port does not require OPER privilege if the port name is not specified in the P4 parameter. In other words, the LAT SETMODE QIO must be to the port corresponding to the CHAN parameter (the forward port attained by assigning a channel to _LTA0:). Note that SS$_NOPRIV is returned if you attempt to change the port type by specifying the LAT$_ITM_PORT_TYPE item code in the P1 itemlist parameter. If the P4 parameter is specified, the LAT port driver also returns SS$_NOPRIV.

Table 5-29 lists the conditions that can occur when an application program issues an IO$M_LT_CONNECT request for a connection to a remote service node. The QIO request is completed when a session is established with the service node. Once the connection completes, data can be read and written to the port with the QIO read and write functions.

On Alpha and Integrity server systems, the IO$M_LT_QUE_CHG_NOTIF function modifier for $QIO allows a process to enable an attention asynchronous system trap (AST), which is used with the LAT $QIO connect request. The IO$M_LT_QUE_CHG_NOTIF function is available only for APPLICATION and FORWARD LAT devices.

If a $QIO connect request has been issued to a remote node and that request has been queued, this attention AST is set each time the queue position changes. This AST can be used as long as the $QIO connect request is queued. Like a Ctrl/Y AST, it is set only once; it must be reenabled after each completion.

If the LAT $QIO connect succeeds or if a LAT connection exists for the intended service, the AST completes with the SS$_DEVACTIVE status code.

If the LAT device does not have the queued characteristic, issuing the IO$M_LT_QUE_CHG_NOTIF function results in the return of SS$_DEVREQERR status code.

The implementation of IO$M_LT_QUE_CHG_NOTIF is shown in the following C example:

 
status - sys$qiow  (
                0,                 /* efn                */
                ltchannel,         /* channel            */
                IO$_TTY_PORT|IO$M_LT_QUE_CHG_NOTIF,
                                   /* function           */
                q_iosb,            /* iosb               */
                0,                 /* astadr             */
                0,                 /* astprm             */
                queue_pos_change,  /* P1 = ast routine   */
                0, 0, 0, 0, 0);    /* P2 through P6 not used */

When a queue position change occurs, the AST routine is called with a 32-bit value. If this value is 0, then the LAT connect $QIO is about to complete, if it has not already. If the value is not 0, the lower word of 16 bits indicates the service queue position, and the upper word of 16 bits indicates the node queue position.

To allow notification by the terminal driver of abnormal termination during I/O operations, enable a Ctrl/Y AST on the channel. This ensures that the terminal driver notifies application programs of an abnormal connection termination. Note that the operating system does not return an AST parameter to the Ctrl/Y AST routine.

When an application with a pending read or write request has an abnormal LAT connection completion, the terminal driver returns a SS$_HANGUP status in the first word of the IOSB. The reason for the abnormal LAT connection completion can be attained with a LAT SENSEMODE QIO request to the port. Search the resulting P1 itemlist for the value corresponding to the LAT$_ITM_DISCONNECT_REASON item code. The value is either a LAT reject code or a LAT facility message. The LAT$V_SENSE_FULL bit must be set in the P3 parameter in order to receive this information.

If IOSB indicates an abnormal completion (SS$_ABORT, see Table 5-29) on a IO$M_LT_CONNECT modifier QIO, the LAT port driver returns the reason for the abnormal completion in IOSB+2. The reason can also be attained with the LAT SENSEMODE QIO function.

The sense mode and sense characteristics functions sense the characteristics of the terminal and return them to the caller in the I/O status block. The following function codes are provided:

IO$_SENSEMODE returns the temporary characteristics of the terminal (the characteristics associated with the current process), and IO$_SENSECHAR returns the permanent characteristics of the terminal. IO$_SENSEMODE is a logical I/O function and requires no privilege. IO$_SENSECHAR is a physical I/O function and requires the privilege necessary to perform physical I/O.

These function codes take the following device- or function-dependent arguments:

The P1 argument points to a variable-length block, as shown in Figure 5-11.

Figure 5-11 Sense Mode Characteristics Buffer

In the buffer, the device class is DC$_TERM, which is defined by the $DCDEF macro. The terminal type is defined by the $TTDEF macro, such as TT$_LA36. The maximum entry for the buffer size (page width) is 255. Table 5-4 lists the values for terminal characteristics. Table 5-5 lists the extended terminal characteristics. Characteristics values are defined by the $TTDEF macro.

The sense mode and sense characteristics functions can take the type-ahead count, read modem, and broadcast function modifiers described in the following sections.

5.3.4.10.1 Type-ahead Count Function Modifier

The type-ahead count function modifier returns the count of characters presently in the type-ahead buffer and a copy of the first character in the buffer. In this case, the P1 argument points to a characteristics buffer returned by IO$M_TYPEAHDCNT. Figure 5-12 shows the format of this buffer.

Figure 5-12 Sense Mode Characteristics Buffer (type-ahead)

5.3.4.10.2 Read Modem Function Modifier

The read modem function modifier allows access to controller-dependent information. The following combinations of function code and modifier are provided:

• IO$_SENSEMODE!IO$M_RD_MODEM

• IO$_SENSECHAR!IO$M_RD_MODEM

These function code modifier pairs take the following device- or function-dependent argument:

• P1—The address of a quadword block

Figure 5-13 shows the format of this block.

Figure 5-13 Sense Mode P1 Block

The receive modem field returns the value of the current input modem signals. Any or all of the following signals can be returned:

• TT$M_DS_DSR—Data set ready (DSR)

• TT$M_DS_RING—Calling indicator (RING)

• TT$M_DS_CARRIER—Data channel received line signal detector (CARRIER)

• TT$M_DS_CTS—Ready for sending (CTS)

• TT$M_DS_SECREC—Received backward channel data (Sec RxD)

The $TTDEF macro defines the symbols for the receive modem field.

The controller type field returns the type of terminal controller in use by the currently active terminal line. The $DCDEF macro defines the symbols for the following types of controllers:

• DT$_DZ11—DZ11 and DZV11

• DT$_DZ32—DZ32

• DT$_DMF32—DMF32

• DT$_DMB32—DMB32

• DT$_DMZ32—DMZ32

• DT$_DHV—DHV11

• DT$_DHU—DHU11

• DT$_LAT—LAT server

	NOTE: For LAT devices, the receive modem field of the IO$M_RD_MODEM function modifier does not return any valid modem signal data. The IO$M_RD_MODEM function modifier is not supported for remote terminals. The status SS$_DEVREQERR is returned in the I/O status block.