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How to optimise interconnected HMI system designs

Posted: 23 Sep 2015     Print Version  Bookmark and Share

Keywords:Internet of Things  IoT 

To develop attractive graphical user interfaces (GUIs), especially within a tight timeframe, it is also immensely helpful to use tools and software that simplify the design and debug process. There are several high-level GUI design tools available today. Some come with a PC-based design tool that lets you drag and drop objects directly onto a digital "canvas" and quickly "wire them up" to sections of your code. Compared to a purely "hand-coded" approach, where graphical objects have to be manually instantiated and manipulated through low-level API calls, this methodology makes it easy to implement functions like buttons, sliders, etc. A GUI emulator is also a highly recommended option as it allows designers to move forward their prototyping efforts without needing to plug in target hardware until the final project integration phase. This provides the designer with real-time, ongoing feedback on the UI, even when hardware development platforms are scarce.

Figure 1: Modern embedded HMI design flow paradigm (Source: Renesas Electronics America Inc.)

There are a number of different embedded HMI software frameworks to choose from today. One such example is Express Logic's GUIX contained within their X-Ware Platform, which includes a high-level GUI design tool, operating system, networking stack, graphics library, and other middleware components. Working GUIs can be put together much like a graphic designer would create a drawing except that the graphical objects can be parameterized and linked directly to functions inside the application to quickly bring the images to life. Using a "what you see is what you get" (WYSIWYG) approach, C code is automatically generated to realise the exact GUI assembled on the tool's canvas. The pixel-accurate GUI can be tested on the PC in Visual Studio, with GUIX and ThreadX running as if the PC were the embedded target. In addition, the GUI can instrumented on the development board to measure performance using a graphical event viewer, called TraceX. Moreover, networking API provided in the TCP/IP stack allows designers to connect their device to the net via IPv4 or to the burgeoning IoT universe via IPv6.

Figure 2: Example embedded design tool (GUIX Studio) (Source: Express Logic, Inc.)

What about hardware?
There are numerous MCU and MPU options to choose from when designing an HMI system. Some designers want the ubiquity of an ARM-based CPU architecture, while others prefer the benefits of vendor-specific CPUs. For example, some vendor's MCUs such as the Renesas RX100 and RX600 series microcontrollers have the ability to execute software instructions in a single clock cycle via an optimised on-chip flash memory and flash memory controller. Whatever your own particular design criteria, the processor you choose should be powerful enough to plough through your heftiest algorithms, yet not with so much overhead as to blow your power budget. Another consideration to keep in mind when choosing a device is to find one for which there is plenty of relevant sample code available and for which you can get support from the vendor.

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