10 Architectural Description

11 INTRODUCTION

This description defines the software required to implement

the ISDN Basic Rate Interface on the HPC family of micro-

controllers including the HPC16400 which has onboard

hardware specifically designed for Data Communication and

ISDN applications

The software consists of the following main parts shown in

overview in

Figure 11

services for the ISDN software and for additional applica-

tion software written by OEM users of the HPC

the HPC16400 and to the TP3420 ‘‘S’’ Interface Device

Q921 and X25 link access procedures (LAPD and

LAPB)

trol Procedures defined in the CCITT Q931 standard

ment engineer at a terminal to make and receive ISDN

phone calls which exercise the above software

minal to monitor the operation of the above software

12 SOFTWARE ARCHITECTURAL PRINCIPLES

121 Modular Multitasking Environment

Eack layer or function is written as a separate software task

Intertask communications and the interface between tasks

and IO drivers is by means of mail messages and sema-

phores which are managed by the multi-tasking HPC Exec-

utive

This modular design and well defined intertask interface

make it easy for users to interface application-dependent

software to the modules provided The services of the HPC

Executive (mail semaphores timers memory management)

facilitate the writing of software tasks and IO drivers

These services are available to all tasks and to interrupt-lev-

el drivers

122 Event-Driven State-Machine Architecture

Telecommunication software typically involves many invo-

cations of the same code (one per call one per logical con-

nection etc) and requires a particular software architecture

tasks must be structured as event-driven state machines

Each task has one or more mailboxes and operates by pick-

ing up mail one message at a time from the mail queue

and processing the message to completion before returning

for the next mail message

Each ‘‘entity’’ within a task (each call each logical connec-

tion etc) has a state block indicating its current state After

picking up a mail message the task identifies the entity in-

volved in the message accesses the state block for that

entity processes the message based on the state of the

entity and finally sets the state block to the new state of the

entity

TLDD10077 – 2

FIGURE 11 HPC16400 Software for ISDN

2