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ND 10130 X-MESSAGE FOR SINTRAN III/VS¶
INTRODUCTION¶
Many data processing applications require the division of a program system into separate, asynchronous processes or tasks, that communicate with each other by sending messages.
This separation may be motivated by security considerations (separation of work-areas, definition of interface points), by hardware design (tasks may run in separate machines), by address space limitations, or simplicity of program development.
By the word task is meant a driver, a direct task, or an RT (foreground or background) program. The X-message (XMSG) system allows tasks to send messages to each other, including handling of memory allocation, queueing, and task synchronization.
A task can open ports through which it can send and receive messages. Data are normally transferred between tasks via message buffers within XMSG. The sending task first opens a port, then reserves an XMSG buffer, transfers data into that buffer and finally informs the receiving task's port that data awaits its collection. Reservation and releasing of messages are done explicitly by the user.
Completion status is returned in the T register, positive (exact significance is dependent on the function) if successful, zero if the operation was not terminated and negative indicating an error.
The functions are divided into two groups: User functions (of general interest) and system functions for finding out what the message system is doing.
SERVICES¶
XMSG Services are invoked by sending messages (using functions) to a defined standard task, called XROUT. It allows tasks to find each other initially by providing a port naming scheme.
It can be considered to be equivalent to the «directory enquiries» service provided by the public phone company, but with the following restriction:
XROUT will never give you somebody else’s telephone number, but will give this person a message sent by you, together with your magic number. The destination task can then look at your message and ring you back, if so desired, and thereby you may be given this magic number.
PRODUCT DESCRIPTION¶
XMSG facilities take two forms: Functions and Services:
Some function and services are privileged. Before calling these, a task must make itself privileged by invoking a special function.
FUNCTIONS¶
XMSG functions are invoked via an XMSG monitor call with parameters being passed in the registers. The T register indicates the particular function required with option bits set in its high order byte when required.
SINGLE- AND MULTI-MACHINE XMSG¶
XMSG can be configured in one of two ways:
- Single-Machine XMSG only provides communication between tasks running in a single ND-100 CPU.
- Multi-Machine XMSG (XMSGMG) also allows communication (but not indirect buffer access) between tasks running in a group of ND-100s.
DOCUMENTATION¶
SINTRAN III Communication Guide . . . ND-60.134
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