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Maximise the processing power of wireless modules

Posted: 25 Nov 2013 ?? ?Print Version ?Bookmark and Share

Keywords:embedded system? processing? wireless module? microcontroller? cellular connectivity?

When embedded designers optimise the often-overlooked processing power within a wireless module they can generally eliminate the system microcontroller, thus creating a cellular-enabled system that is smaller, more efficient, and much cheaper to produce. Following are guidelines for choosing a module that can act as both microcontroller and modem.

When adding cellular connectivity to an embedded system, many designers choose a wireless module because they are pre-integrated components and perform cellular communications with minimum configuration. Pre-certified for use with mobile networks, they're ready for worldwide deployment. The developer interacts with the module using serial interfaces and doesn't have to be concerned with complex aspects of cellular modem transceiver design.

More often than not, designers use a wireless module in combination with a standard microcontroller, usually the two highest-cost items in the bill of materials. The microcontroller manages the application and interacts with peripherals while the module mainly takes care of cellular communications.

However, many wireless modules are capable of doing much more than managing cellular communications since they typically use an integrated chipset that includes a 32bit ARM microcontroller. Accessing this processing power, designers can use the module to manage the entire application. The module can behave as the central processor and modem, eliminating the need for a stand-alone microcontroller. The resulting system is more compact and uses less power, with a noticeably lower material cost.

Figure 1 depicts an example wireless module integrating an ARM9 microcontroller, one the most widely used control architectures in embedded systems.

Figure 1: Detailed block diagram of wireless module, showing ARM9 core.

When the wireless module's chipset was originally designed in the 1990s, the ARM9 was the core microcontroller for a complete mobile phone. Today, in the module's role as an embedded cellular modem, the ARM9's primary function is cellular control, which typically uses less than 20% of its total processing capacity, leaving excess capability available for doing other things.

However, designers can't always assume their wireless module can take on a whole application since not all provide access to the ARM9's excess capacity. Some modules, although using the same basic chipset as fully programmable modules, are shipped with only a subset of the ARM9's pins connected to the external package, leaving its core inaccessible.

Today, designers have several options in choosing modules that provide full ARM core access. Some integrate an ARM946 variation of the ARM9 core with DSP functions often used in ASICs. At least one supplier is developing modules with other ARM cores, including ARM926 and ARM11, so designers will soon have more options.

Although hardware and software requirements vary by application, carefully consider these fundamentals.

To make sure the module's resources can support the full application, check (cheque for banks) for available MIPS and memory resources as well as power consumption, especially if the application will use a battery.

CPU MIPS: The CPU MIPS are shared between the application and firmware for cellular communications. Table 1 gives average CPU consumption per service for a typical 2G M2M module.

Table 1: CPU MIPS consumption per service.

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