Linux for Embedded Systems

Fujitec is a global manufacturer and provider of a complete range of elevators, escalators and other vertical transportation equipment. Nearly all of our products use embedded computers in one form or other. To see the implications, a few features of the elevator business to note are:

We have in the past shipped several products using Linux. We will describe here only one of them—a monitoring display for group controllers (see Figure 1).

Figure 1. Controller Monitoring Display

Another application, a user-interface system for editing scrolling messages in elevator cars, is shown in Figure 2, but we do not have space to introduce it in detail. (Notice the Japanese characters—Linux works fine in Japan, too.)

Figure 2. Elevator User Interface

To put things into perspective, we need a few facts about elevators. If a building has more than 2 or 3 elevators, they are usually working in groups sharing the passenger traffic. A group of elevators is connected to a “Supervisory Group Controller”, which shares the service of each elevator among users while attempting to give each user the illusion that he/she has a personal elevator.

The modern elevator group controller is rather sophisticated; it has to run difficult, optimal-scheduling algorithms in real time. The latest Fujitec models use neural networks for on-line learning and optimization. Without proper tools, the support personnel who perform installation and testing tasks wouldn't understand what is happening with the elevator group.

For maintenance checks, upgrades and occasional troubleshooting, the GSP (Group Supervisory Panel) has a graphical display showing the status of the elevators. This monitoring display was the target of our first Linux application.

Figure 1 shows the graphic screen of the monitor display. Information for each elevator, such as the present floor, traveling direction, door status, registered calls, etc. is indicated by graphic symbols. This screen design has evolved over several years, and it is now familiar to our technical and maintenance personnel.

We built most of the original monitoring display system with custom-designed components:

These components were chosen to give us the following advantages:

Even though we saw several problems with our custom-designed approach and wanted to move to an established, popular platform, until recently it was not feasible.

For the hardware, our first choice would have been the IBM- compatible PC, perhaps in the form of PC/104 cards. However, the dominant commercial OS (first DOS, then Windows), was unsuitable for many reasons. It is neither real-time capable nor reliable, and there is no chance that a particular release could have long-term support from its vendors.

Although there were many alternatives, such as the excellent Lynx OS, none of them satisfied all of our requirements, especially the long-term stability and availability criteria.

With the appearance of Linux, all this has changed.

Over the past few years, several engineers at Fujitec became familiar with Linux. Although we started it as a hobby, gradually the wider applicability of Linux became clear to us.

Our motivation for embracing Linux for product development has several roots:

However, not everything is rosy. Since Linux is essentially Unix, a few things had to be fixed before we could deploy it in an embedded controller.