geostationary telecommunications satellites electronic telephone set ...

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Block design and transfer to
the program library file
The working procedure when designing
the software is summarized in fig.
5. Various parts of the APS system are
used as support in connection with this
design work.
After the required functions have been
divided up between the hardware and
software parts of the block, the internal
function sequence is designed with the
aid of a block flow chart. At the same
time the specific data storage areas
for the block are designed and the program
logic is allocated to the different
priority levels. Furthermore, the required
number of state variable is determined
and also their allocation. Finally
an accurate description is prepared
of the block functions and characteristics.
When designing block flow
charts the flow chart drawing facilities
of the APS system are exploited. Relevant
information is stored in a design
file, which is utilized throughout the
remainder of the design work.
Before the detailed program design
work is started, the different designers
cooperate in order to check the function
and design of the block against
the set requirements and design practice.
A check is then also made of the
real-time requirement and storage volume
of the block, which at this stage
can be foreseen with a high degree of
certainty.
In the next phase the program logic in
the block is designed in source code
form. For this purpose design elements,
for example are utilized which
are automatically fetched from the
program library in connection with the
compilation. Apart from the format
checks, which are performed by the
APS system, a manual check of the
code is made before the block is verified.
After one part of the block is designed,
it is verified by testing. Other completed
parts are then tested, both separately
and together with the other parts
that have already been tested. This
continues until the whole block has
been tested in an environment which
is as realistic as possible. A detailed
description of the testing procedure
has been given in an earlier article in
Ericsson Review 3 .
The source program listings and other
documents, which describe the product
and its application, are now added
to the block description and block
flow chart, in which all design changes
have been entered. These block documents
are then transferred to a document
library file, from where they can
be distributed to the users. At the same
time all computer-stored block information
is transferred to a program
library file. The block is then available
for general use, and a message to this
effect is sent to all potential users.
Coordination at the parent company
In order to achieve designs that are of
high quality throughout and to avoid a
duplication of work in the dispersed
design activities, the coordination of
program designs and development of
design elements, support systems, design
rules and work methods has been
centralized to the parent company in
Stockholm. That this central coordination
activity functions efficiently and
well is perhaps just as necessary as,
for example, good program system
architecture, if it is to be possible to
achieve the previously mentioned
goals for the AKE 13 software.
Handling of design errors
Despite the most rigorous testing routines
during the development of the
software, there is still a risk that there
will be certain design weaknesses or
design errors when newly designed
blocks are taken into service. Consequently
the program system has been
provided with a number of functions
for the detection of such errors, in order
to limit their consequences and to
simplify their correction.
When an error is detected in a block
that has been released for general use,
which may occur during the installation
or when the exchange is in operation,
an error message is prepared. If
the error results in serious operational
disturbances a preliminary program
correction is made at the same time,
which temporarily neutralizes the fault.
The form that this takes is also given
in the error message.