Envoy Application Programming Manual
Table Of Contents
- What’s New in This Manual
- About This Manual
- 1 Application Programming With Envoy
- 7 ADM-2 Multipoint Supervisor Protocol
- 8 TINET Multipoint Supervisor Protocol
- 9 Burroughs Point-To-Point Protocol
- 10 Asynchronous Line Supervisor Protocol
- A ASCII Character Set
- B ASCII to EBCDIC Code Conversion
- C File-System Procedures
- D Statistics Messages
- E S-Series Changes to Envoy
- NonStop™ Himalaya S-Series Server Architecture
- G-Series Migration Considerations
- CBSENSEON and CFSENSEON Modifiers
- LEOTRESYN and NOLEOTRESYN Modifiers
- Treatment of Characters After the Termination Character
- Number of SYN Characters
- DTR Drop
- Reporting of Parity Error
- Half-Duplex Support for Asynchronous Lines
- Controller Replacement
- SYSGEN and COUP
- Unit Numbers
- FDX Line Changes
- No Support for Auto-Call Unit
- Glossary
- Index
Burroughs Point-To-Point Protocol
Envoy Application Programming Manual—427159-001
9-3
Line Contention
Line Contention
With a point-to-point line, both stations can bid for the line simultaneously. Because of
this, one station is designated the primary station and the other the secondary. If both
stations bid at once, the primary has precedence. For Envoy, the primary and secondary
designations are made when issuing the ADD DEVICE command and can be altered by
a call to the SETMODE procedure.
Retries
Line operations are subject to transmission errors in the form of block check character
(BCC) errors, nonresponding remote stations, and incorrect responses from remote
stations. When these types of errors occur, Envoy retries the requested operation.
To specify the maximum number of times that Envoy retries an operation encountering
an error indication, a retry count value is specified for each communication line when
issuing the ADD DEVICE command. The retry count value can be altered with a call to
the SETMODE procedure. If an error condition persists after the operation has been
retried the specified number of times, an error indication is returned to the application
process that requested the operation.
Timeouts
The protocol uses timeouts to resolve contention and detect error conditions. You
specify a timeout value for each line when issuing the ADD DEVICE command. The
timeout value can be altered by calling the SETMODE procedure.
During the WRITE procedure, the timeout value determines the period of time after
sending a message to the remote station that Envoy waits for an acknowledgment from
the remote station. During the READ procedure, the timeout period determines the
period of time Envoy waits for a message from the remote station. Envoy retries an
operation that times out.
File-System Procedures
The application process uses the following Guardian 90 file-system procedures to
interact with Envoy and to communicate with the supervisor station. The file-system
procedures are presented in alphabetic order.
AWAITIO
Waits for completion of an outstanding nowait I/O operation.
CONTROL
Performs the line control functions shown in Table 9-2.