The key differences between the ARM M4 and M55 processors come down to performance, features, and intended use cases. The M55 is newer and more powerful, while the M4 is older and more basic. The M4 is meant for general microcontroller applications, while the M55 targets more advanced IoT and edge processing.
Overview of ARM M4
The ARM Cortex-M4 processor is a 32-bit RISC CPU core designed for embedded and IoT applications. It was first announced in 2010 and is based on the ARMv7-M architecture. The M4 strikes a balance between performance and power efficiency.
Key features of the M4 include:
- 32-bit ARM Cortex-M4 core with single precision FPU
- Clock speeds up to 150 MHz
- Memory protection unit for security
- DSP instructions for digital signal processing
- Timers, GPIO, serial interfaces like I2C, SPI etc.
- Thumb-2 instruction set for better code density
- Embedded trace macrocell for debugging
The M4 is very popular in IoT devices like home automation, industrial control, wireless sensors, motor control, and other embedded applications. It hits a sweet spot between cost, power, and performance.
Overview of ARM M55
The ARM Cortex-M55 processor is a more recent design launched in 2020. It builds on the success of the M4 but adds significant improvements in performance, efficiency, and features.
Key highlights of the M55 include:
- Up to 5x performance boost over M4
- Advanced DSP and ML capabilities
- New Helium vector processing technology
- Scalable clock speeds up to 1 GHz
- Enhanced floating point unit (FPU)
- Memory protection enhancements
- Support for RISC-V code integration
The M55 is designed for more demanding workloads like ML inferencing, advanced signal processing, computer vision, and analytics at the edge. It brings higher-end ARM CPU capabilities to microcontrollers and embedded systems.
Performance Differences
The M55 significantly outperforms the older M4. Some key performance differences:
- 5x higher integer performance
- Up to 15x better signal processing performance with Helium tech
- Up to 2x increase in DMIPS/MHz
- Floating point improvements including double precision support
- Scalable clock speeds up to 1 GHz vs 150 MHz for M4
- Larger memory bandwidth
The jump from 150 MHz max on the M4 to 1 GHz on the M55 is telling. The M55 can reach laptop-class performance levels while the M4 is more basic. This massive performance gain is key.
Feature Differences
The M55 also adds quite a few new features not found on the M4:
- Helium vector processing for advanced DSP
- Improved ML support and SVE2 vector engine
- Enhanced floating point unit
- RISC-V code integration to run alongside ARM
- Support for INT8 and BFloat16 data types used in neural networks
- Memory tagging extension for security
- New TrustZone CryptoCell security block
These features allow the M55 to take on workloads like ML inferencing at the edge. The M4 lacks ML-focused silicon and runs ML very inefficiently.
Intended Use Cases
The M4 and M55 have different intended use cases based on their capabilities:
- ARM M4: General purpose MCU applications, cost-sensitive designs, basic IoT endpoints.
- ARM M55: Advanced signal processing, ML inferencing, computer vision, voice recognition, analytics, next-gen IoT.
You would choose the M4 for simple embedded applications where cost or power efficiency are important. The M55 enables edge intelligence for IoT, with the performance for workloads like image recognition that are not practical on an M4.
Development Environment
Both processors can be programmed using ARM’s MCU development tools:
- CMSIS APIs for managing and accessing peripherals
- MIDLEWARE stacks for connectivity, OS, graphics
- ARM Keil MDK for IDE and compiler
- Mbed OS for rapid development
The M55 allows mixing of ARM code with RISC-V code as well. Overall the development flow is quite similar, with the M55 having added software to leverage its more advanced capabilities.
Use in Microcontrollers
The M4 and M55 cores are used in various ARM MCUs from vendors like STM, NXP, Microchip, Nuvoton, etc. Some examples include:
- STM32F407 – Cortex-M4 MCU by STMicroelectronics
- LPC55S69 – Cortex-M55 MCU by NXP
- EFM32 Pearl – Cortex-M55 SoC by Silicon Labs
- nRF5340 – Cortex-M33 & M55 wireless MCU by Nordic Semi
The M55 is newer, so device options are still limited but expanding rapidly. The M4 has very wide adoption in many existing MCU product lines.
Power Efficiency
Power efficiency is important for embedded and IoT designs. The M4 is on a mature and efficient 40nm or 28nm process. The M55 uses more advanced 22nm/12nm processes. At lower speeds, the M4 can be more power efficient for basic workloads. But the M55 is much more efficient at higher speeds for advanced workloads by finishing tasks faster.
Overall the M55 achieves excellent performance per watt, despite its higher performance ceiling. Its advanced process nodes and architectural optimizations make it very competitive on power efficiency.
Cost Difference
The M4 is older and more established, so it benefits from economies of scale. M4 microcontrollers tend to have lower costs for a given set of features. The M55 is newer technology and costs more per unit. However, the M55 enables far more advanced functionality. So for a target application, an M55 system may require fewer external components and software optimization to achieve the same result. This can reduce Bill of Materials costs.
For high-volume mass market products, the M4 makes sense. For advanced IoT systems, the benefits of the M55 outweigh its incremental cost.
Conclusion
In summary, the ARM M55 is the clear technology leader with significant performance and feature advantages over the venerable M4. It opens up new edge computing use cases thanks to its ML/DSP optimizations. The M4 continues to be a solid choice for mainstream microcontroller applications requiring a balance of cost and capability.
ARM’s MCU roadmap is rapidly evolving to enable increasingly smart and connected IoT end nodes. The jump from M4 to M55 shows ARM’s ambition in pushing its architecture deeper into the embedded world to power the next generation of intelligent tiny devices.
