To achieve small size, low power consumption and fast time to market requirements, embedded systems designers often look to chipsets found in cell phone handsets or mobile internet devices (MIDs) to cost-effectively meet their design requirements. These components, whether they are off-the-shelf chipsets from Intel, AMD or Freescale, or FPGA's from Xilinx, Altera, or Actel, that later migrate to custom ASICS, often define the available storage interfaces. These chipsets are widely understood and supported and more often than not, make use of USB, SD, MMC or some other type of serial programmable interface that is not usually defined with traditional storage such as PATA or SATA.

The SiliconDrive II Blade specification allows for a variety of embedded industry-standard storage interfaces such as embedded USB.

Likewise, traditional flash cards (MMC, SD and their mini/and micro counterparts) or USB thumb drives that connect to these interfaces were originally designed for consumer applications, which have a completely different usage model than an embedded system. Consumer application storage devices are designed to be removable and transportable; they are not designed for the rigors of embedded systems.

Many cell phone or MIDs architectures are moving away from these traditional flash cards because:

  1. Their biggest support costs revolve around the fact that their customers tend to buy the wrong card.
  2. They find that their customers do not upgrade their memory cards every two years; they upgrade their entire MIDs device.

The one thing that all hardware designers know is that whatever the hardware giveth, the software taketh away. So embedded systems designers have traditionally needed to make a value judgment:

  1. Design with a removable, upgradeable storage solution that has inferior environmental characteristics, which means a mounting solution must be developed so that the wireless base station or embedded server can be upgraded three to five years into a 10- year deployment, or
  2. Design with an embedded module like eMMC or any one of the multitude of similar products that needs to be soldered down on the motherboard to meet environmental requirements, but is not upgradeable.

Both of the above solutions are further complicated by the fact that consumer- centric products only have about a one-year lifecycle, so using either solution will necessitate multiple system requalification cycles during a multi-year product deployment.

The only smaller form factor that has gained true adoption in the embedded and enterprise system OEM space has been CompactFlash (CF). CF became the most popular, widely-used form factor in the embedded space for two main reasons. First, people forget that CF was originally developed to be an industrial standard as a smaller alternative to PCMCIA cards. Only with the advent of digital cameras did it become a storage form factor for consumer electronics. Second, CF has stayed around a long time because of the interface modes – mainly IDE (PATA) and PCMCIA memory modes. These modes are well supported by computing chipsets deployed in embedded and military systems. Now, however, even CF is facing major challenges for new designs, primarily because:

  1. Most new chipsets are not supporting PATA interfaces because they require too many pins. The industry has gone away from parallel interfaces in general, preferring the faster serial interface.
  2. The trend in embedded computing is to migrate to smaller form factor boards such as COMs (computer on modules) where CompactFlash is actually too big for the computing platform.

Small Form Factor SSDs

Because of the market evolution and challenges with existing storage options previously described for embedded system applications, there is growing demand for a highly flexible, rugged, and ultra-small form factor solid-state drive (SSD) solution that supports a variety of industry-standard storage interfaces. While embedded computing platforms are using USB, SD, MMC and SATA interfaces, there is no compatible storage solution for space-constrained critical system OEM applications in the netcom, industrial, embedded computing, data center, military and medical markets. To keep up, embedded applications also require a next-generation storage platform that offers faster read/write speeds and enhanced performance and reliability to address critical OEM design considerations such as storage system endurance, elimination of drive corruption, and the ability to forecast useable life, as well as high tolerances to shock and vibration and extreme temperature ranges.

Storage System Usage Models

ImageThe SSD market has emerged in recent years as a large and rapidly growing market that is separate and apart from the traditional consumer flash card market. Today, a broad range of solid-state storage solutions are being offered ranging from high-end, high capacity and high IOPS (Input/Output Operations per Second) products uniquely tuned to meet the requirements of the high performance computing, server and enterprise markets to low-cost, low-end products developed for the commercial computing market, yet each is being marketed as a SSD.

So, to make sense of the plethora of different storage products, form factors and underlying technologies, it is the storage system usage model that should dictate the SSD chosen for a particular application, not the SSD form factor. It is the specific technology requirements of the target market segment that determines the level of technology, performance, reliability, security and ruggedness needed from the SSD. As an example, usage model considerations for embedded system designers may include operating systems storage, storing system configuration information, event or data logging, fast boot features, and power-down event storage.

Standards Drive Adoption

Industries that have adopted standards have realized huge advantages in terms of proven platforms that can be produced in volume with reduced costs, ease of design, and shorter time to market.

Addressing market demand for open standards and the need for second sourcing of products, SiliconSystems has contributed its SiliconDrive II Blade specification to the Small Form Factor Special Interest Group (SFF-SIG) for the purpose of creating an official governing standard. The SFF-SIG has a growing membership of embedded computing suppliers who are interested in advancing small form factor designs and adoption. An SFF-SIG working group has named the new standard "MiniBlade". Under the MiniBlade standard, the SFF-SIG will define a wide-array of storage, communications, GPS and other I/O products. The new MiniBlade specification will define the pin-out and mechanical form factor. This is the first step for standardizing an ultra-small mass storage solution for the small form-factor embedded system market. Members of the SFF-SIG will have full access to the new MiniBlade pin out and mechanical form factor specifications, and will be able to engineer their SSD to suit their independent product and market goals.

The attraction to SFF-SIG and the advantages of adopting the SiliconDrive II Blade specification is the ruggedness of the new form factor's latching connector, which can be designed in either a vertical or right-angle position for additional design flexibility. While the connector locks down holding the SSD securely in place, the SiliconDrive II Blade can also be removed for upgrades to the system throughout its deployment lifecycle. Another key advantage is the size of the SiliconDrive II Blade – it is a quarter of the size of a CompactFlash card.

Design Flexibility

With the new SiliconDrive II Blade specification, OEM designers are no longer constrained by designing an application around the "size" of the storage option. With rugged, scalable, advanced storage form factors, designers can rethink every aspect of the design. Additionally, the SiliconDrive II Blade's 40-pin design supports multiple interfaces such as USB, SD, MMC and SATA, giving the OEM designer maximum flexibility to choose the host system interface that best optimizes their application. Now with a 40-pin connector, a designer for an application such as a system controller hub could choose to run signals for USB, SD, MMC and SATA simultaneously. With very little redesign, the same board could accommodate a different, upgraded, or faster storage device if the application warranted. Also, there is nothing that limits using the connector for storage; any interface-compatible device could be used.

The SiliconDrive II Blade specification includes the ruggedness of the latching connector that can be designed in either a vertical or right-angle position.

In many cases, manufacturers have to make serious design trade-offs in price, performance and reliability when designing for smaller component process geometries. In consumer applications like a Smart Phone, if the application fails, a call is dropped or maybe an address book is corrupted. If a handheld heart rate monitor fails, a life may be lost. Unlike consumer applications, critical embedded systems demand high reliability. The SiliconDrive II Blade design incorporates all the patented technologies for high performance and high reliability and multi-year product life that are packed into larger form factors such as 2.5-inch SSDs. Design flexibility is enhanced without the need to make design compromises.

Data Center Application

To demonstrate a real-world application for the SiliconDrive II Blade, a data center server that supports a rack of disk drives is using the SSD for cache transfer storage. The server application caches data over a storage area network, and in the event of a power-down situation or system failure, will "dump" the cache to the SiliconDrive II Blade. The 4 MB capacity of the SiliconDrive II Blade is equal to the DRAM cache in the system so the cache can be transferred quickly and effectively if an event occurs.

Summary

There has never been a storage form factor specifically designed for the embedded systems market. OEM designers have had to select the "Best of Class" storage option available to them at the time, with many of the solutions having been originally designed for consumer applications.

Consumer demand for small form factor handsets and MIDs drove the invention and introduction of new, ultra-small, standards-based SSD form factors, but did not specifically meet the requirements of the embedded systems market. Embedded system applications required a more rugged, upgradeable form factor that provided the high performance, high reliability, multi-year product life and a low total cost of storage ownership that were previously unavailable in consumer- based flash cards.

New embedded system form factors like SiliconDrive II Blade are designed for the most demanding 24/7 usage models and suitable for a wide variety of enterprise system OEM applications, ranging from industrial control and automation equipment, data center applications, wearable computers for the military or video streaming, and surveillance applications.

This article was written by Mark Diggs, Director Systems Engineering, SiliconSystems, Inc. (Aliso Viejo, CA). For more information, contact Mr. Diggs at This email address is being protected from spambots. You need JavaScript enabled to view it., the SFF-SIG at This email address is being protected from spambots. You need JavaScript enabled to view it., or click here.