The Arm Cortex-M4 is a 32-bit processor core designed for embedded and IoT applications requiring low power consumption and high performance. It offers speeds up to 150 MHz and is capable of reaching 1.25 DMIPS/MHz. This translates to real-world clock speeds of 80-150 MHz and performance in the range of 100-187 DMIPS.
Key Speed and Performance Specs
Here are some of the key speed and performance specifications for the Cortex-M4 processor:
- Clock speed: Up to 150 MHz
- DMIPS/MHz: 1.25 DMIPS/MHz
- Dhrystone MIPS: 168 MHz at 1.25 DMIPS/MHz = 210 DMIPS
- CoreMark score: 230 CoreMark/MHz
- Memory bandwidth: 2.7 GB/s with 150 MHz bus frequency
- DSP performance: 150 MHz at 1.25 DMIPS/MHz = 187 DMIPS
Real-World Performance
In real-world applications, the Cortex-M4 usually runs at 80-150 MHz. This results in actual performance of:
- 100-187 DMIPS
- 80-150 CoreMark
- 1.0-2.25 GB/s memory bandwidth
For comparison, here’s how Cortex-M4 performance stacks up to other common cores:
- Cortex-M0: 48 DMIPS at 48 MHz
- Cortex-M3: 105 DMIPS at 105 MHz
- Cortex-A5: 850 DMIPS at 850 MHz
As you can see, the Cortex-M4 hits a nice sweet spot between the lower-end Cortex-M cores and more powerful application processors like the Cortex-A5.
Workload Performance
In addition to the synthetic benchmark results above, here is an overview of how the Cortex-M4 performs on common workloads:
- Sensor processing: The Cortex-M4 can process data from multiple sensors in real-time, including analog, temperature, pressure, inertia, and gyroscopic sensors.
- Motor control: It can handle closed-loop control algorithms for single or multiple electric motors.
- Audio: The M4 can encode/decode various audio formats like MP3, AAC, etc. in real-time.
- Graphics: With its DSP extensions, it can process 2D/3D graphics for basic GUIs and displays.
- Connectivity: It can easily handle protocol stacks like USB, Ethernet, Wi-Fi, and Bluetooth.
Overall, the Cortex-M4 hits a sweet spot for embedded applications that need more performance than an M0 or M3, but don’t require the power of an application processor.
Performance Boosting Features
The Cortex-M4 architecture includes several features to boost performance on embedded workloads:
- DSP extensions: Allow more efficient digital signal processing for audio, image/video, and sensor algorithms.
- SIMD instructions: Vector operations that perform the same function on multiple data points concurrently.
- Accelerators: Hardware acceleration for common functions like cryptography and memory protection.
- Deterministic operation: Real-time performance with minimal interrupt latency.
- Memory architecture: Supports flash, SRAM, and high-speed external memories.
Leveraging these features allows the M4 to punch above its weight class in terms of throughput and latency-sensitive applications.
Power Efficiency
In addition to performance, the Cortex-M4 shines in power-constrained applications thanks to its power optimized architecture. Key attributes include:
- Dynamic voltage scaling: Clock and voltage can scale dynamically based on workload to save power.
- Sleep modes: Quickly enter and exit sleep modes to reduce active power consumption.
- Integrated FPU: Hardware floating point unit reduces power vs. software emulation.
- Memory architecture: Optimized for lower voltage memories like flash, SRAM, etc.
Together, these attributes allow the M4 to deliver excellent performance per watt. Typical figures are 1.25 DMIPS/MHz and 230 CoreMark/MHz at low operating voltages.
Example Cortex-M4 Devices
The Cortex-M4 CPU core is used in a wide range of system-on-chips (SoCs) and microcontroller units (MCUs) from companies like:
- STMicroelectronics: STM32F4 series
- NXP: Kinetis K and L series
- Microchip: SAM4 series
- Cypress: PSoC 4000 series
- Silicon Labs: EFM32 series
- NordicSemi: nRF52 series
These devices cater to many embedded applications including industrial automation, motor control, smart home, consumer electronics, and IoT endpoints.
Conclusion
The Arm Cortex-M4 hits a sweet spot between performance and power efficiency in the 32-bit embedded processor space. With real-world clock speeds of 80-150 MHz, it delivers 100-187 DMIPS along with advanced DSP and floating point capabilities. The M4’s scalable architecture allows it to handle workloads ranging from sensor hubs and motor control to wireless protocols and audio processing. Coupled with excellent power optimization, the Cortex-M4 will continue to be a go-to choice for demanding yet power-conscious embedded and IoT applications.
