2 Transactions

AMS communications are carried out as a series of ‘transactions’. A transaction consists of an initial message and a number of further messages (replies) in either direction, associated with the initial message. Separate transactions are used to set up a communications path and to carry out the business of obeying a command. A command transaction is started by calling ams_send and is terminated as described under ‘Getting Expected Replies’ (see Section 7).

When sending a message, the user specifies a message_function and a message_status which are passed as arguments to functions ams_send or ams_reply.

The value of message_function may be:

MESSYS__INIT

Used to ask for a communications link to another task. (ams_send only)¹.

MESSYS__DE_INIT

Used to close a communications link to another task.

MESSYS__MESSAGE

Used for all other purposes and qualified by the message_status and possibly other arguments.