Envoy Application Programming Manual

ADM-2 Multipoint Supervisor Protocol
Envoy Application Programming Manual—427159-001
7-25
Line Action by Procedure Call
General file-system errors (Table 7-7) are also possible.
Line Action by Procedure Call
This subsection describes the ADM-2 control sequences transmitted because of calls to
file-system procedures. It also describes the actions of file-system procedures in
response to line states and the reception of selected control sequences.
This subsection includes:
•
READ Procedure on page 7-25
•
WRITE Procedure on page 7-28
•
WRITEREAD Procedure (Transmit a Send Function) on page 7-31
READ Procedure
The READ procedure is used to initiate the polling sequence and read a message from a
terminal. While messages are being read, the line is in a READ state. The line returns to
the CONTROL state when the terminal sends an EOT sequence (to indicate the
completion of a transmission).
Initial READ (Line in CONTROL State)
An initial READ (Example 7-9) causes Envoy, on behalf of the application process, to
begin polling all addresses in the poll list. If a terminal does not have a message to send,
it responds with an EOT sequence, and polling continues to the next terminal in the poll
list.
Polling continues until a station responds with a message, an error occurs (such as a
nonresponding station), or the specified number of passes through the poll list have been
made. Upon successful receipt of a message from a terminal, the line enters the READ
state and a condition code of CCE is returned. The address-list entry number of the
terminal that responded with a message is returned in the message control word, bits
<8:15>.
Table 7-7. General File-System Errors
Error Code Description
10-29 Coding or access problem
30-33 System configuration problem
120-199 Device hardware problem
200-255 Path error