Steering, acceleration, braking and parking assistance systems, lane departure warning systems — there are more and more systems that help us to drive our cars. They offer greater performance, greater comfort, and greater safety. Nevertheless, in the latter case, they themselves need to satisfy strict functional safety standards. These are defined in two standards.
IEC 61508 declares four safety integrity levels (SILs) for industrial control systems (see table). ISO 26262, on the other hand, applies to safety-critical electrical/electronic (E/E) systems in automotive vehicles. It defines the safety levels ASIL A to ASIL D, where ASIL A represents the lowest risk potential, and ASIL D represents the highest. The level is determined based on frequency, controllability and severity of the accident and/or damage. ISO 26262 is based on IEC 61508, but specifically accommodates concerns specific to the automotive industry. These include in particular controllability, or the ability of a driver or other traffic participants to prevent damage or an accident in a given scenario.
NOR Flash in Safety-Critical Systems
In numerous advanced driver-assistance systems (ADAS), NOR flash memory plays a key role as part of a safety-critical system, because this non-volatile, programmable memory is robust, reliable and fast. The host processor can execute code directly from the flash memory without having to copy it to external DRAM first. This makes NOR flash memory ideal for code execution, not just in the car but also in industrial robots and other IoT machinery and devices. Another advantage is its large temperature range, allowing it to be used in a wide variety of environments and applications in the vehicle.
Common uses for NOR flash memory in automotive and industrial applications include:
- permanent storage of code, data and images for use during start-up,
- EEPROM emulation (i.e. storage of safety-critical data),
- continuous reading during runtime, and
- Code execution directly from flash memory.
Depending on the application, the requirements for each of these workloads varies. Systems expected to satisfy high functional safety standards, however, require a new approach.
More than Just Commodity Memory
Infineon has developed Semper NOR Flash especially for functional safety needs. It includes an embedded ARM Cortex-M0 as well as function blocks for diagnosis, data integrity, and reliability. They provide functions such as SafeBoot and Safe Reset, ECC (Error Correction Code) and Sector Protection. The AEC-Q100-qualified Semper NOR Flash therefore offers ASIL-B-compliant function safety with the possibility of ASIL-D support, with up to a million write cycles and 25 years’ data retention even at extreme temperatures of between –40°C and +125°C. The integrated error correction support corrects single-bit errors and detects multi-bit errors (SECDED).
Long-Term Availability as a Safety Factor
The development of safety-compliant systems usually requires a large number of carefully considered, complex decisions regarding design, evaluation, testing, and certification. The product life cycles of the systems are therefore usually long, covering many years. Redesigns are usually very expensive and difficult. This makes the long-term availability of all components a critical factor. However, memory in particular rarely offers availability of more than three to five years. For the Semper NOR Flash range, Infineon guarantees availability of over ten years. The range introduced here is the first generation of an entirely new platform offered by Infineon. It excels in particular in two respects. Firstly, the memory handles many processes that could not previously be covered by this component, which reduces the load on the microcontroller. Secondly, it is compliant with the JEDEC Expanded SPI Standard. This makes Semper NOR Flash memory an ideal solution for industrial and automotive applications.
A comparison of safety levels under IEC 61508 (SIL) and ISO 26262 (ASIL).
The architecture of the Semper NOR Flash memory combines an ARM Cortex-M0 with numerous safety functions.
For more information and a direct ordering option, please visit our e-commerce platform at www.rutronik24.com.
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