Constraints - Printronix SL4M Reference Manual

Chapter 1

Constraints

Constraints
•
UCP (for GPIO) and PXML cannot be used at the same time in the
system. Only one can be active at any time.
•
Only one client may connect to the management port at a time.
•
The client is responsible for maintaining the TCP management
connection to the printer; reconnect as necessary. The management
connection may be lost at any time due to printer power-down or network
failure. Responses will be lost when the management connection is down
since there is no caching or retransmission mechanism.
•
It is possible for a client to connect to the management port in the middle
of a response message, which at the same time is being sent to a
previous client. This is possible if the connection to the previous client is
dropped before the message is complete. It is the responsibility of the
new client to read and discard the remainder of the message.
•
All responses are not synchronized, so a message immediately returned
after a command may not be the one that applies to the command. The
messages are in XML format and are guaranteed to be complete
messages, except when the management connection is lost and
reestablished while a message was being sent from the printer.
•
XML messages must start with the <?xml> header so that invalid
messages can be ignored by the printer.
•
The TCP transport mechanism does not provide a separate framing
protocol, so the input stream must be processed by an XML parser to
determine the end of a message. Alternatively, message framing can be
determined by searching for the <?xml> header, then capturing all data
until the </pxml> trailer is found.
•
One response may span more than one message to relieve the printer
from having to buffer output messages. Messages that form a single
response are guaranteed to be sent in the correct sequence, and a flag is
provided to denote the final message of the sequence.
•
For firmware download, the client is responsible for waiting for the printer
to enter download mode before sending data. The client is responsible for
waiting until the printer fully boots with the new firmware before sending
configuration data.
•
Notification of start and end of print job must be initiated by some other
means, typically be placing PTX_SETUP commands in the print data
stream.
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