Software Architecture - Siemens ST950 Handbook

5.2

Software Architecture

The significant parts of the software in the Traffic Controller can be divided in to the
following main parts:
The Primary CPU controls and monitors the traffic signals, while a second CPU also
monitors the traffic signals:
In the LV controller the PHP CPU monitors the traffic signals and also plays a
part in controlling the traffic signals through its control of the phase bus
communications (this is handled by the Primary in the ELV controller).
In the ELV controller, the SEC CPU monitors communications between the
Primary CPU and the lamp switch cards.
These are critical parts of the software and form part of the safety case of the
controller. For this reason, this embedded real-time firmware resides in discrete
microprocessors.
The Application software parts provide the external interfaces to the user and other
equipment, such as a Traffic Instation. This software is required to be more powerful
and easier to update. For this reason, this software uses the LINUX Operating System
and resides on a more powerful processor; the EFC CPU.
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Figure 12 – Software Architecture
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Paul Cox
ST950 General Handbook
Mobility Division, Traffic Solutions
Sopers Lane, Poole, Dorset, BH17 7ER
Page 67 of 107
Status Issued
Date 16-Jul-2015
Document No. 667/HB/46000/000
Mobility is a division of Siemens Plc