CP6100 I/O Process Programming Manual

Using CP6100: Programming
• The CP6100 I/O process. This process provides the file system
interface for one or more application processes to communicate
with up to 15 lines attached to the same 6100 subsystem. (One
subsystem can have more than one pair of CP6100 processes.
You assign processes to specific lines with the SYSGEN
program.)
• A protocol task. A protocol task runs in an LIU on the 6100
subsystem, and controls the line attached to that LIU. The
task receives application requests from the CP6100 I/O
process, satisfies the requests (for example, for data
transfers or line control functions), and replies to CP6100.
NOTE
An LIU actually has two components: the Communications Line
Interface Processor (CLIP), in which the protocol runs, and
the Line Interface Module (LIM), which provides the electrical
interface.
CP6100 accepts requests from applications and routes them to
protocol tasks running in the 6100 subsystem. When a request
completes, CP6100 replies to the application, delivering status
information from both the file system and the protocol task. A
condition code indicates request status according to the file
system and CP6100; information from the protocol appears in a
field of the reply message. (Because of how work is divided
between CP6100 and the protocol, each is in a position to
recognize different kinds of errors. There will be more
discussion of errors later in this section). If a request
involves a data transfer to or from the line, CP6100 gets a
buffer and transfers the data between the application and the
protocol task.
Figure 2-1 shows the interaction between an application, a CP6100
I/O process, and a protocol task. The depiction is slightly
oversimplified: In fact, there are some requests CP6100 handles
by itself, rather than send them to the protocol task; for
example, a DEVICEINFO request is satisfied in the Tandem host,
without access to the line or its controlling software. Also,
multiple applications can use the same line, or a single
application can use multiple lines (possibly involving multiple
instances of CP6100).
2-2