Summary

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This chapter covers a tremendous amount of information. The Project Trailblazer engineers started off by establishing their input and output requirements for lift monitoring and snow-making control through discussions with the Operations Department. They investigated I/O boards and decided on PC parallel port use. They then designed an interface circuit to connect a PC parallel port to an input module board and an output module board. When they began writing control software, three approaches evolved: port I/O using inb and outb functions, parallel port control using the Linux ppdev device driver, and development of a custom device driver. The port I/O approach was simple. However, its use had drawbacks that make it too risky. The second approach, using ppdev, didn't solve the drawbacks. The engineers decided to develop a custom device driver, liftmon_snowcon. This driver presented the developers with an easy-to-use interface (that is, files in the /proc directory) for lift monitoring and snow-making control. The driver hides interface circuit-specific knowledge from the developer and provides an eloquent interface for bash scripting. The liftmon_snowcon device driver development was a little more complicated than the use of port I/O, but the benefits far outweigh the costs.

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