Incredible innovation is driving the technological shift in vehicles, but there is one thing that must continue to be front and center: the safety of drivers, passengers, and road users. Arm technology has been under the hood for decades and we understand that automotive technologies require processors suited to safety applications that still address the wider power, cost, area, and software considerations of our partners. In this blog, we talk about the recently updated Arm Cortex-M23 processor, which now features enhanced capabilities for automotive applications.

Arm Cortex-M processors are area and power efficient, making them a great fit for a broad range of automotive applications. They are also easy to program, as a large ecosystem of software and tools supports them, and they have a simple programmer’s model.  Building safety relevant products can be costly, in both time and effort. To speed up time-to-market for automotive partners, Arm has added even more functional safety capabilities to M-profile cores and certified them with an external assessor for ISO 26262. This elevates the safety starting position for chip designers, easing their safety efforts, and allowing them to focus on other areas. With the release of the updated Cortex-M23, the full portfolio of Cortex-M processors, including Cortex-M85 and Cortex-M55, now include leading-edge functional safety features.

The updated Cortex-M23

Within all vehicles, there are small, single functions that need cost-effective compute solutions. It is in this space that achieving functional safety within the constraints of low power and area is an ongoing challenge. Cortex-M23 is Arm’s most power efficient Cortex-M CPU and has been updated to include functional safety features that elevate diagnostic coverage for safety critical applications. Examples include ultrasonic parking sensors for parking assistance, tire pressure and rain sensors, lighting and LED controllers for headlights and brake lights, to name a few. Many of these applications require ASIL B, a medium level of integrity, for which the updated Cortex-M23 could be the perfect fit with its single core safety mechanisms.

An area and power efficient solution

ASIL B level normally requires the detection of 90 percent of single point faults, and that transient faults are addressed, if applicable. You can learn more about ASIL B in our Cortex-M55: Functional safety ready blog, where we outline the different ASIL levels defined by ISO 26262. Transient faults are tricky in that they can go easily undetected. This is because a particle could hit an area of the design and flip one bit of data, but it is not long before the next bit of data is written to that location, overwriting the flipped bit.

The updated Cortex-M23 adds transient fault protection to address this issue for applications that are constrained by area and cost where a dual-core lockstep approach would be undesirable. It also adds interface protection for the detection of faults at the boundary of the CPU, removing more work at the system level for chip designers. The use of a Software Test Library for Cortex-M23 would also provide more diagnostic coverage of permanent faults, complementing the internal core safety mechanisms. Moreover, these additional features have no impact on benchmark performance compared to the previous Cortex-M23, making adoption simpler.

Not forgetting ASIL D

For applications where dual-core lockstep is required, Arm has now delivered a new Dual Core Lockstep application note specific to Cortex-M23. This document gives guidance on how to implement this feature on Cortex-M23 and what to watch out for when implementing it. This might also be the right solution for an ASIL B application if your design can support the additional die area and power that comes with a dual lockstep implementation.

Cortex-M23, a reminder

Cortex-M23, which was first launched in 2016, implements the ARMv8-M architecture, bringing more instructions and system level features. Those experienced with Cortex-M0+ see many of the same energy-efficiency benefits in Cortex-M23. These benefits include deep-sleep modes and sleep-on-exit, which make it ideal for low-power applications. With more vehicles becoming electrified, Tier 1s must develop solutions that can meet the power needs of OEMs, for which Cortex-M processors are well suited.

Developers can design more robust and safer systems using the optional MPU (Memory Protection Unit). The MPU can be programmed to define regions of memory, assign certain attributes and access permissions depending on the task. When an application attempts to access a region of memory for which it has not been authorized, the MPU can trigger a fault exception.

A full functional safety portfolio

Cortex-M23, Cortex-M55, and Cortex-M85 are a scalable collection of Cortex-M processors that can support a wide range of automotive applications, from low power consumption to high-performance needs. They share a common architecture for ease of code portability. A broad ecosystem supports them, including safety certified software and tools, to simplify development for the next generation of vehicles. 

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