Leeway is an outstation operating system and programming environment. It uses a block structured language, where blocks are drawn on a page, and joined up with a mouse, to define the way in which a process is controlled. It was developed for a Water Company in the South East, and runs on PC-based equipment. One of the fundamental design criteria for the design was that the original software should be able to run on the new hardware without modification, so that existing process control did not have to be re-engineered, and staff did not have to be re-trained.
Leeway is a block structured language for process control. It consists of a number of block types, from simple digital switches to sequence logic blocks and three term controllers. Blocks are configured by drawing them on a canvas, and then joining inputs to outputs. A small amount of extra configuration must be done by entering data into the blocks directly.
For cases where the standard blocks are not adequate, two types of User blocks can be configured. These enable users to configure the inner workings of a block,rather than just the external connections. A number of such blocks can be built into a library, so that a well-designed block can be used on a number of outstations.
The software was developed in response to a situation where the original hardware on which the code ran was obsolete, but the costs of replacing the hardware with a non-compatible system would have been swamped by the costs of re-engineering and retesting the software system. Leeway runs on PC-based hardware, and initially, code from the original 6809-based outstations could be run as-was, without any need to re-test the functionality. Many developments have been made since, but ease of use and ease of upgrade has been a primary consideration.