The Cortex-M55 and Cortex-M7 are both 32-bit microcontroller cores designed by ARM for embedded and IoT applications. The main differences between the two cores come down to performance, features, and intended use cases.
In brief, the Cortex-M7 is the higher performance and more capable core, while the Cortex-M55 is optimized for power efficiency. The M7 has a 3-stage pipeline allowing higher clock speeds, more advanced caches, and DSP extensions for signal processing. The M55 has a shorter 2-stage pipeline focused on low power operation, with basic caches and no DSP extensions. The M55 is aimed at cost-sensitive and battery-powered devices where efficiency is critical, while the M7 targets more demanding applications needing maximum performance.
Architecture and Performance
The most significant architectural difference between the Cortex-M7 and M55 is their CPU pipelines. The Cortex-M7 uses a 3-stage pipeline, compared to a shorter 2-stage pipeline in the Cortex-M55. Pipelines break a CPU instruction down into multiple stages – fetch, decode, execute, etc. More pipeline stages allow for higher clock speeds but also increase power consumption.
The M7’s 3-stage pipeline enables much higher performance than the M55. Some key differences in peak capabilities include:
- M7 can reach 300+ MHz clock speeds, M55 maxes out below 150 MHz.
- M7 delivers 1.25 DMIPS/MHz, while M55 provides just 0.9 DMIPS/MHz.
- M7 can perform dual-issue instructions, M55 is single-issue.
In real-world conditions, this can translate to 2-3x higher overall performance from the Cortex-M7 versus the M55 at the same clock speed. Of course, actual implementations will depend on factors like the Cortex version, manufacturing process, and system design.
Features and Capabilities
Beyond just the CPU pipeline differences, the Cortex-M7 includes a number of features and capabilities not present on the M55:
- Caches – M7 contains 16-64KB instruction cache and up to 64KB data cache, improving performance. M55 has just basic prefetch buffers.
- FPU – M7 includes an optional single or double precision floating point unit. M55 has no FPU.
- DSP – M7 incorporates optional DSP extensions and instructions for digital signal processing. Lacks on M55.
- SIMD – M7 provides ARMv7E-M SIMD instructions for vector operations. Not available on M55.
- Memory – M7 supports MPU and MMU for improved memory management. M55 only has basic MPU.
The Cortex-M7 is essentially designed as a microcontroller version of the Cortex-A series processors. It leverages features from those higher-end application processors to boost performance. In contrast, the M55 is intended as an extremely efficient but simpler 32-bit processing solution.
Use Cases and Applications
The strengths and weaknesses of each core make them suited for different use cases:
Cortex-M7
The Cortex-M7 excels in application areas such as:
- Industrial – Servo control, robotics, motor control, sensors, etc.
- Automotive – ADAS, digital instruments, engine control units, body electronics.
- Consumer – Digital cameras, high-end wearables, smart home hubs, mid-range mobile.
- Medical – Diagnostic equipment, digital healthcare products, clinical devices.
Its high-performance 32-bit capabilities, DSP extensions, extensive memory and peripheral support make it a flexible choice for IoT, embedded, and real-time applications requiring complex processing.
Cortex-M55
The Cortex-M55 is more targeted for applications including:
- Simple IoT devices – sensors, trackers, monitors, controllers, etc.
- Wearables – activity bands, smartwatches, medical trackers.
- Smart home and appliances – lighting, security, appliances.
- Industrial automation – simple motion control, instrumentation.
Its design for ultra low power operation makes it suitable for basic embedded and IoT applications with a need to maximize battery life.
Example Implementations
Looking at actual ARM-based chips using these two cores shows their differing targets:
Cortex-M7 Microcontrollers
- STM32F7 – high-performance automotive, industrial, and consumer MCUs.
- NXP iMX RT1050 – crossover MCU bridging Cortex-M and application processors.
- Microchip SAM E70 – industrial-focused MCU with motor control and DSP.
- Renesas RE Family – automotive MCUs for instrument clusters and infotainment.
Cortex-M55 Microcontrollers
- Nordic nRF5340 – optimized for cellular IoT applications.
- Cypress PSoC 64 – ultra-low-power IoT and wearable MCU.
- NXP iMX RT500 – basic industrial IoT and motor control.
- STM32L5 – mainstream MCU for health/fitness wearables.
Vendors utilize the M7 for their highest performance 32-bit ARM offerings, while reserving M55 for simpler low-power products.
Conclusion
In summary, the Cortex-M7 is designed to provide maximum 32-bit computational throughput for complex embedded and real-time workloads. It leverages an advanced 3-stage pipeline, extensive caches, DSP extensions, and other features to enable this high-performance operation.
In contrast, the Cortex-M55 focuses on ultra low power operation for basic IoT and embedded applications where battery life and cost are critical factors. Its shorter 2-stage CPU pipeline and lack of advanced features result in lower peak performance but maximize efficiency.
For system designers, choosing between the two cores involves weighing factors such as processing requirements, power constraints, BOM cost, and target applications. The Cortex-M7 brings 32-bit performance to embedded projects needing more horsepower, while the Cortex-M55 fits ultra low-power devices requiring minimal compute capabilities.
