Envoy Application Programming Manual

Burroughs Point-To-Point Protocol
Envoy Application Programming Manual—427159-001
9-9
Line Action by Procedure Call
Line Action by Procedure Call
This subsection describes the Burroughs point-to-point line-control sequences
transmitted because of calls to file-system procedures. It also describes the actions of
file-system procedures to line states and the reception of selected control sequences.
This subsection includes:
•
READ Procedure on page 9-9
•
WRITE Procedure on page 9-12
•
CONTROL Procedure (Send EOT) on page 9-15
•
CONTROL Procedure (Enable RVI) on page 9-15
READ Procedure
The READ procedure is used to initiate the polling sequence and to read messages
containing data from a responding tributary station. While messages are being read, the
line is in the READ state. The line returns to the CONTROL state when the tributary
station sends an EOT sequence to indicate the completion of the transmission.
Initial READ (Line in CONTROL State)
An initial READ causes Envoy, on behalf of the application process, to wait for a line
bid from the remote station (Example 9-1).
If a line bid is received, Envoy acknowledges the line bid, receives the initial message
and returns the message to the buffer of the application process. The successful receipt
of the initial message is indicated by a condition code of CCE upon completion of the
READ. Following receipt of the initial message, the line is in the READ state.
Note that the initial message from the remote is not acknowledged by the initial READ.
The following READ acknowledges the initial message.
If no line bid is received within the timeout interval (presumably because the remote has
nothing to send), the READ completes with error 171.
Example 9-1. Initial READ (Line in CONTROL State)
Local Remote
line state = CONTROL
CALL READ(...)
| <-- ENQ (bid)
| ACK -->
| <-- message
(READ completes)
error = 0
line state = READ