The Cortex-M4 is an advancement over the earlier Cortex-M3 microcontroller core from ARM. It builds on the strengths of the M3 design while adding several key features to improve performance, efficiency, and capabilities. Some of the most significant enhancements of the M4 compared to the M3 include:
Floating Point Unit
One major addition in the Cortex-M4 is the inclusion of a single-precision floating point unit (FPU). The FPU allows the M4 to directly support floating point math operations in hardware. This removes the need to emulate floats in software, which is much slower. The hardware FPU makes floating point arithmetic up to 10 times faster than before. This greatly benefits applications using 3D graphics, physics simulations, signal processing, and other computationally-intensive tasks involving floating point numbers.
Digital Signal Processing
Building on the FPU, the M4 adds DSP capabilities to accelerate digital signal processing algorithms. It includes instructions for efficient digital filtering, matrix operations, and Fast Fourier Transform. For DSP-centric applications like audio processing, software-defined radio, motor control, and so on, the M4’s DSP features provide a significant performance advantage.
The Cortex-M4 memory architecture also sees improvements for higher performance. It doubles the number of core registers from 16 to 32. The M4 has a TCM (Tightly Coupled Memory) interface to supplement the existing SysTick timer. TCM offers faster access than external memory for time-critical tasks. There is also optional instruction cache support to speed up execution. And the M4 core can perform some operations directly in memory without CPU intervention.
While the M3 is a single-core design, the M4 adds support for dual-core Symmetric Multi-Processing (SMP). This enables a chip to contain two M4 cores that work cooperatively as a multicore system. The dual-core approach delivers greater processing power for multithreaded and parallel workloads.
For debugging and tracing software execution, the Embedded Trace Macrocell (ETM) built into the M4 has been upgraded significantly from the M3 version. It has more trace memory, wider trace bandwidth, and additional tracing modes. This gives greater visibility into program flow, data access, timing, and interrupts during development. Trace device drivers are also standardized for simplified integration.
Unlike the M3 core, the M4 includes optional integer hardware divide support. This performs divides up to 4 times faster in hardware rather than software emulation. Hardware divide is useful for efficiency in operations like managing link lists, hash tables, statistics, signal processing, and matrix math.
For applications requiring secure processing and cryptographic functions, the M4 offers optional security extensions. These include instructions for faster AES encryption/decryption, SHA-256 hash generation, and other cryptography algorithms. A true random number generator is also included. This improves security for communication protocols, digital rights management DRM, and other features relying on encryption and security.
The M4 builds on the M3’s support for different application environments. This includes additional operating modes beyond just Thread and Handler mode in the M3. New modes include Privileged and User mode, along with Memory Protection Unit (MPU) support. These features help to separate trusted code from un-trusted user code for more robust security and reliability.
For battery-powered and energy-aware applications, the M4 core provides flexibility in power management. Dynamic voltage scaling allows the CPU voltage and speed to be adjusted on the fly for slower speed at lower power when peak performance is not needed. There is also support for multiple low power sleep modes to substantially reduce power draw during idle periods.
A range of advanced peripherals are available on M4 MCUs depending on the specific chip implementation. These can include enhanced communication interfaces like USB OTG, CAN-FD, Ethernet MAC, and Bluetooth Low Energy. Other advanced I/O includes touch sensing, TFT graphics controllers, and improved ADCs and DACs. These richer peripheral sets cater to more sophisticated application requirements.
The ARM ecosystem provides a wide range of development tools supporting the Cortex-M4. Compilers include ARM Compiler, GCC, IAR, and Keil MDK-ARM. Debuggers include ARM DStream, Lauterbach, Segger, and tools from silicon partners. RTOS and middleware support includes CMSIS libraries, FreeRTOS, Micrium uC/OS, and ARM Mbed. And for IoT applications, the M4 works with the ARM Mbed cloud platform.
Licensing and Fabrication
As with earlier Cortex cores, ARM offers flexible licensing models for the M4. Chip makers can license the M4 design for custom ASICs, or use M4 in off-the-shelf MCUs. The M4 is licensable to semiconductor companies and foundries worldwide. It is supported by all major foundry processes from 180nm down to 5nm. The Cortex-M4 is implemented in silicon by over 250 different ARM partners, providing one of the broadest selections among 32-bit embedded cores.
Performance and Efficiency
In CPU throughput, the M4 outperforms the older M3 by up to 60% depending on the application. Clock speeds range from 50-300MHz at lower process nodes. The M4 achieves 1.25 DMIPS/MHz and 2.6 CoreMark/MHz. The optional FPU delivers up to 1.6 GFLOPS. Code density is excellent at less than 1.2 mm2 in 40nm. Dynamic power ranges from 180-215uW/MHz. The enhancements in the M4 translate to stronger overall performance, greater energy efficiency, and smaller silicon area versus the M3.
The Cortex-M4 targets a wide spectrum of embedded applications. Its versatility makes it popular across the automotive, industrial, consumer electronics, IoT, and general-purpose MCU markets. Common applications include:
- Advanced driver assistance systems ADAS in vehicles
- Motor control for industrial robots and machinery
- Smart sensors for IIoT and predictive maintenance
- Wireless connectivity in wearables and hearables
- Voice command processing in smart speakers
- Biometric security and authentication
- AR/VR headsets and glasses
- Control systems in drones and robotics
For these use cases and more, the Cortex-M4 hits a sweet spot between performance, power, and cost to serve a diverse range of embedded needs.