Overcoming design constraints for fast processors in ultra-compact mobile platforms

The fundamental considerations for designing mobile platforms haven't changed since the introduction of the first portable computer.

4Although processors are getting faster, embedded design problems are not changing drastically. Engineers still face the same power, size, software development, thermal management, and I/O issues that typically complicate designs. New form factors like the recently introduced Mobile-ITX platform promise to help resolve these concerns while providing greater flexibility in portable devices.

While it might seem that the latest mobile computing platforms present a new set of challenges to designers, the core issues have not changed significantly since the introduction of the first portable computer. Trade-offs between computing capacity and power consumption, evaluations of size and weight versus battery life, and software development needs still demand consideration. Picking the right mix of capabilities often means the difference between a best-selling product and a flop.

ARM-based solutions have recently garnered a great deal of attention. While the latest generation of ARM-based CPUs delivers higher processing speed, designers must assess other issues besides performance, such as requirements for supporting circuitry and embedded software development. Furthermore, because many of these solutions are aimed at the cell phone market, they might not meet the needs of other mobile applications.

Size, weight, and battery restrictions

Processor limitations have traditionally driven development requirements for new mobile computing devices. Consequently, lack of CPU horsepower hindered the availability of features such as multitasking. This problem is rapidly disappearing with the latest generation of mobile processors. The greater dilemma at present is addressing I/O requirements while maintaining reasonable size and weight.

Power is the most critical design constraint of any mobile platform as it determines everything from battery life to size and weight. Today’s consumers expect mobile devices to be small, lightweight, and portable with all-day battery life regardless of the application. Unfortunately, battery capacity has not increased enough to maintain pace with the demand for more powerful computing platforms. CPU power consumption must be kept to an absolute minimum and power-on-demand techniques must be implemented to respond to the varying levels needed.

Size and weight often take a backseat to other requirements but should not be neglected. Specific battery capacity translates into a fairly well-defined amount of space needed when it comes down to the final requirements cut. Batteries also represent one of the least standardized elements in portable devices of all shapes and sizes. Reducing the size of components such as the CPU and supporting devices can help keep the overall size, weight, and battery space to a minimum.

Other critical design requirements

Software development usually comprises the largest chunk of the design budget and drives the overall schedule for any new consumer product. Building around an industry-standard x86 core can mitigate risks associated with the development of key software components and enable developers skilled in more traditional applications to capitalize on the millions of lines of code written for x86-based computers.

Heat dissipation is a problem often associated with high-performance CPUs. Designers must use creative techniques to ensure that heat does not relegate their device to the defective pile. Prototyping with production-representative development boards can reduce this risk while giving engineers insight into the implications of their designs. Low power consumption translates into low heat generation and the need for some type of cooling technique.

Whereas software development and thermal management concerns demand attention, I/O issues often drop to the bottom of the requirements list when the need to cut back on weight or power arises. However, consumers frequently make purchasing decisions based on whether they can or cannot connect things to their mobile devices. Many new products have been criticized for their lack of expandable memory or storage in the form of a microSD slot or USB connector. Having an architecture that supports the most common I/O requirements provides the desired flexibility to add or delete the physical connections based on other criteria.

Mobile-ITX meets needs for portability

The new Mobile-ITX platform from VIA Technologies directly addresses many of these design considerations. The first Mobile-ITX product, EPIA-T700 (Figure 1), is a 60 mm x 60 mm Computer-On-Module (COM) incorporating the C7-M Ultra-Low Voltage (ULV) 1 GHz CPU along with the VX820 All-in-One Multimedia System Processor and supporting ICs, delivering the latest x86 processor technologies while maintaining compatibility with existing software applications and design tools.

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Figure 1: The Mobile-ITX COM form factor measures at 60 mm x 60 mm.
(Click graphic to zoom)

The C7-M ULV processor was specifically adapted for the Mobile-ITX platform. Its ultra-small die size of 5 mm x 7 mm fits neatly within the new 11 mm x 11 mm mobileBGA package, enabling a highly compact PCB design (see block diagram in Figure 2).

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Figure 2: Packaged in a mobileBGA design, Mobile-ITX includes a tiny C7-M ULV CPU and Enhanced PowerSaver technology for efficient processing.
(Click graphic to zoom by 1.9x)

This small packaging coupled with the highly efficient and responsive Enhanced PowerSaver architectural design translates into about 1 W of power required when running in the optimized low-voltage mode. Table 1 shows the maximum system power supply budget.

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Table 1: Running at 5 V, Mobile-ITX provides the low power consumption required in mobile devices.
(Click graphic to zoom by 1.5x)

Mobile-ITX runs from a single 5 V DC power source, reducing the need for complex power-conversion circuitry and the overall power requirement while simplifying battery and power-distribution needs. As shown in Figure 3, the platform standardizes around two 120-pin connectors to carry all I/O signals and power. These connectors allow designers to easily prototype and develop against the final hardware solution.

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Figure 3: I/O signals in Mobile-ITX are mapped to two high-density, low-profile connectors with a distance of 3 mm between the CPU module and the baseboard.
(Click graphic to zoom)

The board design distributes the larger ICs to help with heat dissipation, so there is no additional cooling requirement. With its compact size and power-saving functions, the Mobile-ITX platform offers all the advanced graphics and I/O support needed for any mobile computing device.

Selecting the right platform

Designing for today’s mobile computing market involves a number of challenges. Demand for mobility dictates ever-increasing processor capacity with continually decreasing power requirements. Competition pressures designers to bring new products to market faster. Embedded software development costs multiply as devices become more complex and sophisticated.

Building on the venerable x86 platform can go a long way toward reducing these costs while accelerating time to market. Choosing the right platform to base a new product on is critical to its overall success. Understanding the important design issues and researching how different vendors address them is the key to making the right choice.

Joseph Chung is technology advocate at VIA Technologies Inc., based in Taipei, Taiwan. He has worked at VIA for 12 years and is currently responsible for the company’s embedded component business in North America. He also chairs the SFF-SIG Pico-ITXe work group. Joseph received his BS in Electrical Engineering and BS in Computer Engineering from the University of Kansas.

VIA Technologies
www.viaembedded.com