Playing the cards with embedded devices

Intel originally designed the Pentium M processor for mobile systems, such as notebooks, to meet the special requirements in this area, such as high-performance, low-power consumption and a flat design without a cooling fan. Nevertheless, these same characteristics also predestine this processor for embedded applications, which is why it has rapidly found wide acceptance in this market segment.

The standard configuration for embedded applications is currently the Pentium M processor with the 855GME chipset. The Pentium offers numerous advantages for embedded applications, including SpeedStep power management for efficient energy use, several processor options for good scalability and highly integrated functionality for high performance.

Furthermore, the standard interfaces and uniform driver support that have been implemented ensure that software-development costs remain within clear bounds.

Intel's long-life program for processor and chipset ensures availability for several years and provides investment security for future products.

System integration

Modular technology offers many advantages for developing new products, which is why a variety of modular designs (SOM, system-on-module) in the embedded field - such as ETX, UTX, ITX, DIMM-PC, X-Board, smartCore and smartModule, PC/104, and DIL-PC as well as several proprietary module solutions - have either already established themselves or are increasingly gaining pre-eminence.

Today, the main benefit connected with using these module concepts can be seen less in the second-source aspect, which usually does not work anyway, but rather in factors such as scalability, reduced time to market and the opportunity to reapply know-how gained in previous work.

The smartModules developed by Digital-Logic are small multichip modules that offer all the functionality of a PC as well as scalable CPU power from a 586 to a Pentium M.

Nearly all signals, interfaces, ISA and PCI buses are combined on a single bus, the smartBus855, and integrated into the user-specific environment via two connectors with 320 contacts.

Since the smartBus simultaneously serves as the technology interface, future smartModules will also be mechanically, electrically and functionally compatible. The smartModule's design makes it possible to quickly and inexpensively integrate complex PC technology into user-specific products.

In this way, the developers of individual serial devices become less dependent on the change cycles for the PC hardware and can integrate future process technologies into their applications without major changes.

Using smartModules in the development of new products reduces design efforts and development costs. They represent a solution when user-specific electronics are necessary or prescribed and the space constraints and environmental conditions do not allow the use of a standard PC board.

Nevertheless, when the modules are used, employing the latest technology is not the only factor to be considered - reliability, deliverability and flexibility during development are also important.

Design-in

Despite the module concept and the design, there are some important aspects to consider when integrating Pentium M modules into systems.

With embedded assemblies, 'traps' can be expected in connection with the following requirements:

• Compact or closed design without a fan;
• Special housing shapes;
• Special display or lack of a display;
• Few peripherals for debugging/testing measures;
• Special environmental conditions (temperature/degree of protection, EMC), industrial-strength power supply;
• Shock, vibration or other mechanical loads.

Another criterion that is crucial for the product's stability is the existence of a cooling concept. This is because the processor and chipset act as hotspots that develop a heat output with peaks of up to 25 W and additional components such as the switching power supply generate further heat.

Since temperature-sensitive components, such as the hard disk drive, CD/DVD or CompactFlash, are frequently in the device, heat must be led away from the elements that generate it (CPU and chipset) to the outside. Additionally, designers should avoid hotspots in the device and implement monitoring functions per software.

With regard to the power supply, one must keep in mind that it is not the average power consumption that is the decisive factor, but the impulse load: in load moments, the processor and chipset consume up to 50 W of power in the ms range. The PWM core power supply also strains the main supply on an impulse basis (5 VDC up to 8 A).

Moreover, all additional peripheral components require further power. With typical values of 0.9 to 1.41 V, the voltage fluctuations for the core supply are extremely sensitive and have an enormous influence on the energy balance. At low voltages and higher currents, the layout and contacts are critical design factors.

SpeedStep technology also requires a dynamic switching controller load for the principal voltages. To achieve optimal values when configuring the supply, it is helpful to perform a precise analysis of the system components and use a switching controller with a high degree of efficiency and a higher intermediate voltage (12 to 20).

In the same way, an integrated solution can be used with module concepts.

On the SM855, the core voltage is generated by a PWM module that processes inputs of 4.75 to 30 VDC of modern POL designs (distributed supplies).

Beyond that, Digital-Logic recommends approved switchmode power supplies from power supply vendors, suggests reference circuits from its own products and offers its own PC/104 power supply for Pentium M assemblies.

An additional advantage can be gained by using a higher supply voltage, since this causes the current to sink considerably.

That results in a lower critical load on the conductor tracks, decreases the load on the connectors and reduces EMC radiation.

The Intel chipset only supports low pin count and peripheral component interconnect interfaces for connecting peripheral components. PCI, however, is often too complex and oversized for simple I/O peripherals.

The usual PC interfaces - such as PS2, COM, LPT, floppy disk or USB - are not available on a standard basis either. Nevertheless, this problem can be solved with an LPC-to-ISA bridge and LPC-SuperIO, which can be integrated into the base board.

Many embedded systems with LC displays (such as medical devices, automotive electronics, terminals, etc) were integrated via the TTL interface and an adapted graphical BIOS.

Since the Pentium processor and the 855GME chipset use the digital visual interface as a standard display interface, the use of DVO TTL adapters is an appropriate solution.

Moreover, it is possible to evade the BIOS adaptation with a PnP identifier and EDID files (automatic recognition of the display).

Design reliability

In the future, PCI-Express and S-ATA will play an important role in the embedded area because they:

• Have fewer connector pins (and thus a smaller form factor) and require reduced board effort;
• Feature higher data rates (PCI-Express: 2.5 Gbps, about three times the PCI rate; S-ATA: 1.5 Gbps, about 1.5 times as fast as P-ATA);
• Enable interference-free data transmission through differential signal transmission;
• Are hotplug-capable.

The SOMs currently available do not yet have PCI-Express and S-ATA is only taken into consideration in individual cases. For systems with higher data throughput rates, such as measuring systems, loggers, etc, PCI bandwidth can quickly become a 'bottleneck', and the Pentium's scalable CPU performance can only be used on a limited basis.

Each SM855 smartModule is already prepared for PCI-Express and S-ATA with two channels each and design-in support is available through reference designs.

Intel's product strategy for Pentium M and the 855GME chipset makes operating system support easier for mobile and embedded systems. This means that it is basically possible to use all standard operating systems from the desktop, such as Windows 2000/XP, Linux, QNX and VxWorks.

Embedded operating systems, such as Windows XP-Embedded, Windows CE.NET and Embedded Linux/RT-Linux, are also supported.

Other advantages include the driver and middleware support provided through specialised partners as well as the ELinOS port support package for SM855/MSEBX855.

Small Pentium-M module

In the form of the SM855 smartModule, Digital-Logic is offering what it claims is currently the world's smallest Pentium M computer module for industrial applications. The computer module is based on the Intel-855GME chipset with a 400 MHz front side bus and employs a Pentium M processor clocked at speeds of 0.6 to 2 GHz.

Equipped with a 2 MB L2-OnDieCache, the 1.8 GHz Pentium M 745 reaches performance levels comparable to a 3.4 GHz Pentium 4 processor. With the aid of DDR-SODIMM modules, the SM855's main memory can be equipped with 256 MB to 1024 MB DRAM.

The CPU and memory are mounted so that they can be exchanged, but are mechanically protected against vibrations or shock due to the encapsulated design.

Since it supports all the 855 chipset's energy-saving functions, the SM855 consumes 6 to 20 W.

Another strength of the module is its high-performance graphics equipment. The SM855 uses the Extreme Graphics video controller that is integrated into the 855GME chipset and supports DirectX 9 compatibility with up to 64 MB of video memory.

The video controller has two separate video outputs (VGA analog and DVO/LVDS) for controlling two independent monitors. The standard package also includes six USB-2.0 interfaces, an AC97-V2.3-compatible audio interface with DTS-5.1 output and a 100/10 Base-T port for fast network communication.

Moreover, a hardware monitor, an efficient wide-range power supply for core voltages and progressive ACPI power management functions have been integrated into the SM855.

All peripheral and bus interfaces are collected on the smartBus855, which is also prepared for PCI-Express and S-ATA.

The SM855 requires a supply voltage of 3.3 or 5 (4.5 up to 30), and it runs on all operating systems commonly in use. Equipped with a Flash BIOS with a dual-BIOS option, it allows booting from diverse media (such as the hard disk drive, floppy disk, USB, IEEE 1394 or PC card) or via LAN.

The module works in the standard temperature range from -20 to +60°C. It is tested with Screening E48, and is also approved for the extended temperature range of -40 to +85°C at low clock rates (600 MHz).

The SM855 features a cooling concept, in which the smartModule cover is optimised for heat dissipation. The cover is made from a high-strength, milled aluminium block with a fixed bearing system all around the circuit board and it has a special copper core mounted on the CPU.

The surface, which is 100% level, enables an ideal connection to the enclosure wall of a device or a heat sink.

Configured for a low power consumption, the SM855 is especially predestined for battery-operated systems.

The PC module is tested for shock and vibration and is suitable for applications in the areas of navigation, telecommunications, computer peripherals, medical and testing equipment, and aerospace engineering as well as in automotive electronics and in internet terminals.

The form factor of the smartModule allows a very compact design in connection with a PC/104 expansion.

Among other things, the company uses the PC module as the basis for its embedded computer products such as PC/104, EBX, Microspace-PC, and customer-specific designs.

* Before taking up his current position, Andreas Geh founded his own engineering company for industrial electronics concentrating on embedded computer technologies. He instituted the concept of including embedded computer, embedded Linux, and embedded communication as basic technologies for systems.