Computer-on-Module Boosts Functionality of PC/104 CPU Boards

By Peter Kannegiesser, LiPPERT Embedded Computers

PC/104 modules are still very popular for embedded PC systems. In fact, they’re widely used in industrial automation, remote data collection, and other applications. These small, stackable modules permit the simple construction of miniature computers that are flexibly configurable while providing a comprehensive scope of interface options. Many independent vendors offer a wide range of off-the-shelf peripheral cards for almost each and every specific interfacing task.

Because the original PC/104 specification is based on the mature ISA bus interface, it has historically been easy for system builders to develop even quick one-off solutions for more exotic requirements. However, the ISA bus has become increasingly obsolete in modern chipsets. On the other hand, today’s chipsets come with interfaces that are indispensable. PCI-Express, USB 2.0, Gigabit Ethernet, and SATA are only a few examples. Unfortunately, implementing a custom peripheral expansion using PCI-Express, for example, requires much more engineering effort.

Even with the much higher bandwidth of today’s buses, many applications are difficult to handle due to the non-deterministic nature of the bus structures. Compared with the simple parallel ISA bus structures, this can be a major obstacle for the development of any specific solutions. Nevertheless, there is hope. Silicon vendors still recognize the need for compatibility with old but proven technology. They therefore offer a number of bridging devices that can be used to integrate the latest-technology PC products into well-established legacy systems. Using these bridging devices, the PC/104 ISA interface can be retained when building embedded systems while state of the art interfaces get attached too.

An example of how this can be done is LiPPERT Embedded Computers’ Cool LiteRunner-ECO. This PC/104 processor board is a single-board computer featuring the familiar and easy-to-use legacy interfaces like ISA bus, PS/2, and serial ports. It also comes with USB 2.0, SATA, and Gigabit Ethernet interfaces, thereby allowing seamless integration with today’s ubiquitous, handy, and inexpensive peripherals. At the heart of the board is a tiny advanced computer-on-module (COM), dubbed the CoreExpress-ECO. This central-processing-unit (CPU) module is equipped with an Intel® Atom® processor, Z530, an Intel® System Controller Hub US15W, and up to 2 GBytes of random access memory (RAM). CoreExpress modules provide a legacy-free, digital-only interface to the carrier board, making the integration process straightforward. There are no issues with crosstalk or other signal distortions. Because of the single connector interface, frequently encountered mechanical problems with the connectors’ placement are eliminated.

As explained previously, the PC/104 specification is based on the ISA bus interface. Because the CoreExpress-ECO module does not support the ISA bus directly, ISA is implemented on the PC/104 carrier using an LPC-to-ISA bridge. That bridge is fully transparent for the software. As a result, no special initialization or drivers are required from the application.

The serial, parallel, and PS/2 interfaces are handled by an additional Super IO controller, which is configured by the BIOS. An additional transceiver converts the SDVO signal into legacy VGA. Via a PCI Express switch, two Gigabit Ethernet channels are connected to a PCI-Express lane as provided by the CoreExpress-ECO module. While complying with the PC/104 specification, the Cool LiteRunner-ECO uses an internal PCI Express infrastructure to improve the performance of any PC/104-based system (see Figure 1).

Figure 1: The infrastructure of this processor board allows it to comply with the PC/104 specification while enhancing the performance of PC/104-based systems.

The resulting processor board can be used with all of the legacy off-the-shelf peripheral modules that are available (see Figure 2). It promises to fit nicely into high-speed networks while supporting all types of USB gadgets.

Figure 2: The Cool LiteRunner-ECO processor board features PC/104 with Gigabit LAN and SATA.

Support for CoreExpress® COMs is increasing. The tiny CoreExpress modules, which were introduced in 2008, have recently gained support from other embedded PC-hardware vendors. In addition, the Small Form Factor Special Interest Group (SFF-SIG) adopted the CoreExpress specification via member vote and made it an open standard. The newly released version 2.1 of the standard contains a number of enhancements that were proposed by SFF-SIG members during the evaluation and discussion phase. It is upward compatible with the previous proprietary version.

Three characteristics establish the CoreExpress specification as the first of a new generation of COMs. First, the connector used by CoreExpress modules has been confirmed to operate at the speeds required for PCI Express Generation 2. Secondly, the specification contains an option to configure the SDVO interface pins for the new DisplayPort interface. Finally, sufficient reserved pins are included in the definition to enable the inclusion of at least two USB 3.0 ports in a future release of the specification. In closing, using today’s computer-on-modules on carrier boards with bridges to legacy interfaces provides an easy method to reuse existing knowledge. It also allows designers to leverage the hardware and software solutions that are freely available.

Peter Kannegiesser works as project manager at LiPPERT Embedded Computers. Before joining LiPPERT, he worked with ABB doing PLC system software development including real-time software, OS kernel, PLC functions, industrial communications, utilities, and development environments. Kannegiesser also has experience in hardware and software development for alarm systems and building control systems. For more information about LiPPERT, visit www.lippertembedded.com, or e-mail info@lippertembedded.com.