How to Make Embedded System Design More Resilient in the Face of Supply Chain Disruption
07 August 2023
Figure 1: The dimensions of the 4 standard OSM form factors (Source: iWave)
Manufacturers of embedded systems have long known about the benefits and trade-offs of basing designs either on discrete microprocessor components or on a ready-made system-on-module (SOM). This is often referred to as the Make or Buy? dilemma.
Buying in a complete modular solution, which provides the microprocessor with its supporting components (such as memory and a power management elements) on a single, compact PCB, saves a substantial amount of development time. It frees specialist digital designers to work on differentiating aspects of a product design. But a modular solution’s bill-of-materials (BoM) costs are often higher than that of the equivalent discrete components. In addition, when using discrete components the designer has the freedom to make the design in any form factor, or with any non-standard component or technology elements.
These arguments are well understood by OEMs - but a new factor affecting the choice is perhaps less so - the benefits of designing for resilience. The problems currently plaguing the car industry show how much economic damage can follow from severe disruption in the semiconductor supply chain. When a design is reliant on a single source of a key component that is not easily substituted, the production line is then at the mercy of that component’s supply channel - that component is the product’s weakest link in the chain.
The causes of volatility in the semiconductor supply chain
The microprocessor is the key point of vulnerability in an embedded device OEM’s supply chain, because of the advanced technology on which it is based. Embedded hardware that run on Linux or Android operating systems require high-performance processors that use the latest packaging, high-speed interface and DRAM memory technologies. This means that every microprocessor family is a unique part based on proprietary technology, and has just one source. In many cases, the microprocessor is also supported by dedicated companion chips, which will also usually be a single-source part.
Component shortages or extended lead times can also hamper a factory’s ability to maintain normal production operation. If this happens, it is not easy for the OEM to quickly implement a Plan B. Microprocessor substitution is difficult, taking considerable development effort and time. Supply chain disruption to the either microprocessors or companion chips may cause an embedded system OEM’s production line to be halted, resulting in substantial financial impact. This has important bearing on Make or Buy? decisions, because the use of a SOM helps to insulate OEMs from supply chain issues.
Avoiding development risks
In addition to the supply chain risks that OEMs are exposed, development risks arise from implementing microprocessor-based design. Such risks come from 2 key design elements:
• The small pitch of BGA packages calls for specialist layout expertise to design the fan-out from the microprocessor. Special production machinery and a high-cost multilayered PCBs are also mandated.
• High-speed bus interfaces and high-speed DRAMs both require expert design capabilities. Dedicated CAD tools are used to configure the track timing, impedance, isolation characteristics, and shape of the PCB routing to be compatible with the tolerances specified by IC manufacturers.
If the OEM decides to make rather than buy, then, it is exposed to the risk of a single source of supply, alongside the requirement to manage dedicated engineering teams, and undertake a long and complex development process. Even when a development is completed, the OEM must install advanced production equipment and processes to manufacture a high-cost PCB.
Figure 2: An iWave ITX SBC iW-RainboW-G50S SOM
SOM: Offloading the risks
OEMs which choose the buy rather than make option shift the risks on to the provider of the SOM, in relation to microprocessor sub-system development and maintenance, porting the design to new versions of the chip’s software development kit (SDK), implementing chip upgrades and managing device end-of-life (EoL).
In return for the premium paid via the SOM’s higher unit cost, the OEM gains several valuable benefits:
• Product designers can concentrate on unique features which provide added value.
• SOMs are supplied in standard form factors - so if the SOM supply from one manufacturer fails, it can be replaced by one from a different manufacturer featuring the same microprocessor.
• The standard footprint also enables OEMs to migrate a design from one generation of a microprocessor family to the next without redesigning end-product hardware. This capability also supports development of end-product designs with low-end, mid-range and high-end versions.
• Use of a SOM dramatically shortens development time, resulting in faster time-to-market.
The new Open Standard Modules (OSM) form factor was developed under the aegis of the Standardisation Group for Embedded Technologies (SGeT). It provides numerous benefits, including:
• Increase I/O density.
• Meeting demand for smaller, lower-cost embedded computer modules.
• Offering pin-compatible options for swapping between different IC manufacturers and different Arm processor architectures.
• Support the development of product families with different I/O options via the provision of four pin-compatible form factors - thereby eliminating the need to redesign a product’s carrier board for each new end-product variant.
Already, these form factor options are well supported by commercial suppliers of OSM modules. For instance, iWave supplies OSM modules featuring microprocessors from NXP, Renesas and STMicroelectronics.
Table 1: OSM modules available from SOM manufacturer iWave
When Future Electronics supplies an iWave OSM module to an embedded system OEM, it can also provide a rich choice of supporting technologies - including a single-board computer for application porting and testing, and associated components (like camera modules, TFT displays, enclosures, heat sinks, wireless modules, GNSS positioning sensors, etc.
By using an OSM embedded computer module, which has a standard footprint, I/O provision, functions and pin locations, design engineers can base multiple product designs on a single carrier board while retaining the ability to switch from one MPU to another. This minimises the OEM’s exposure to supply-chain risk, and makes a design resilient: with a SOM, the OEM can replace a microprocessor which is unavailable or on allocation with a different microprocessor, without the need for a hardware redesign. Because the OSM standard is available in four standard footprints, the OEM can build a product family with feature sets ranging from simple and basic with the Zero OSM option up to a highly integrated, high-performance unit based on a Large OSM module, capable of offering a high number of I/Os, and supporting advanced capabilities such as Wi-Fi® and Bluetooth® wireless communication, high-speed cameras, AI functions, etc.
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