Embedded Systems Design Europe - November 2007 - (Page 36) user interface The tradeoffs involved in building a UI can be many. Making the right choices can make or break your system. Build the right UI for your complex system BY COLIN WALLS AND GEOFF KENDALL T 36 he implementation of a sophisticated user interface (UI) brings a number of interesting challenges. It often leads to tradeoffs between the cost and difficulty of implementation versus the quality of the user experience. In the consumer space, the UI can make or break a product and have a lasting impact on a vendor’s product line. Let’s first look at the different types of facilities and mechanisms found on today’s typical UI. Processing a user’s interactions with buttons and switches is quite straightforward. It’s simply a matter of polling an interface frequently enough or responding to an interrupt. There are a few subtleties to keep in mind. For example, a switch or a button being pressed may be seen as a transition from “1” to “0,” not vice versa as might be expected. Also, switch contacts have a tendency to bounce and without care, can be interpreted as a sequence of actuations. Lamps are equally as simple. They’re typically illuminated by setting a bit in a device register. This has a small challenge: registers are typically “write only” so the software can’t read back the current state (a shadow copy of the data must be kept in RAM and used with care). Flashing lamps require some type of timing mechanism. This might be handled by a simple clock interrupt service routine, or a real-time operating system (RTOS) may be employed for the main application, which can accommodate the timing requirements. Simple alphanumeric displays are handled in much the same way as lamps. NOVEMBER – DECEMBER 2007 | embedded systems design europe | www.embedded.com/europe 036-037-038_ESDE.indd 36 6/11/07 16:24:58 http://www.embedded.com/europe
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