Envoy Application Programming Manual

BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-23
READ Procedure
Continuation READ (Line in READ State)
All READs following the initial one are continuation READs. A continuation READ
causes Envoy (Example 5-5), on behalf of the application process, to send the proper
acknowledgment for the preceding message, read the next message, and return the
message to the buffer of the application process. The successful receipt of a message is
indicated by a condition code of CCE upon completion of the READ.
The line remains in the READ state until an EOT sequence is received from the
supervisor station. The line then reverts to the CONTROL state, causing Envoy to
resume monitoring the line for polling and selection sequences. The READ receiving the
EOT sequence does not complete until a station whose poll state is active is polled or a
station whose select state is active is selected.
The continuation READ remains outstanding; it is not acknowledged until a subsequent
READ is received. Table 5-10
lists the file-system errors that may occur on a
continuation READ.
177 Text overrun. The length of the message received
exceeds the length specified in the read count
parameter. The READ was attempted the number
of times specified by the retry value.
CONTROL
178 No address list was specified. CONTROL
Example 5-5. Continuation READ
Tributary (Local) Supervisor (Remote)
line state = READ
CALL READ(...)
| ACKn -->
| <-- message n
(READ completes)
MCW.<1> = 0 (READ type = continuation READ)
error = 0
line state = READ
CALL READ(...)
| <-- EOT
line state = CONTROL
Table 5-9. Initial READ File System Errors (page 2 of 2)
Error State Description Resultant Line Number