The Cortex-M4 and Cortex-M7 are both widely used 32-bit ARM processor cores targeted at embedded and IoT applications. The Cortex-M7 is more powerful and has additional features compared to the M4, but also costs more. For many applications the M4 provides sufficient performance at a lower price point.
Overview of the Cortex-M4 Core
The Cortex-M4 core from ARM is a very popular 32-bit RISC processor optimized for embedded and IoT applications requiring low power consumption and good real-time responsiveness. It has a von Neumann architecture with a single bus interface fetch/decode/execute pipeline.
The M4 instruction set is optimized for high code density and efficiency. It includes Thumb-2 technology for improved performance compared to earlier Thumb instruction sets. Key features of the Cortex-M4 core include:
- 32-bit RISC architecture with Thumb-2 instruction set
- 3-stage pipeline fetch/decode/execute
- Up to 150 DMIPS performance at 150 MHz
- Built-in DSP extensions and single-cycle MAC for digital signal processing
- Memory protection unit (MPU) for real-time OS support
- Low power design with efficient pipeline and power gating
The Cortex-M4 is manufactured on advanced silicon processes down to 40 nm for an optimal combination of performance, power and cost. It is commonly used for applications such as motor control, industrial automation, human-machine interfaces, IoT edge nodes, and consumer devices.
Overview of the Cortex-M7 Core
The Cortex-M7 is ARM’s high-end core designed for advanced microcontroller and embedded applications requiring very high performance. It builds on the Cortex-M4 design and adds a number of significant enhancements.
Key features of the Cortex-M7 core include:
- 32-bit RISC architecture with Thumb-2 instruction set
- 5-stage microarchitecture pipeline
- Superscalar dual-issue for simultaneous fetch and execute
- Up to 300 DMIPS performance at 300 MHz
- Optional extended single instruction multiple data (SIMD) unit
- Tightly-coupled memory (TCM) for low-latency access
- Sophisticated branch prediction and prefetch
- Advanced interrupts and exception handling
- Memory protection unit (MPU) with 8 regions
- Optional ECC on memories and hardware cryptographic accelerators
The Cortex-M7 achieves very high performance while still maintaining power efficiency for embedded applications. It is manufactured on advanced processes down to 28 nm.
Detailed Comparison of the Cortex-M4 and Cortex-M7
Let’s go through some of the key microarchitecture differences between the Cortex-M4 and Cortex-M7 in more detail:
Pipeline Depth
The Cortex-M4 uses a 3-stage pipeline — fetch, decode, execute. This simpler pipeline reduces power consumption but limits performance. The Cortex-M7 has a deeper 5-stage pipeline allowing higher clock frequencies and greater parallelism for higher performance.
Superscalar Execution
The Cortex-M7 core can perform simultaneous dual-issue execution, fetching and executing two instructions in parallel each cycle. The M4 core is limited to fetching and executing a single instruction per cycle.
Processor Optimization
The M7 implements more advanced branch prediction, speculative execution, and instruction prefetch compared to the M4 to optimize instruction throughput and efficiency. It has larger TCM for low-latency access.
DSP extensions
Both the Cortex-M4 and M7 have basic DSP extensions like single cycle multiply-accumulate (MAC) instructions. The Cortex-M7 adds optional SIMD capabilities for handling vector DSP workloads efficiently.
Memory Protection Unit
The Memory Protection Unit (MPU) allows safe execution of multiple processes in a real-time OS. Both cores have MPUs, but the Cortex-M7 MPU provides 8 configurable regions vs. 4 on the Cortex-M4.
Error Correction and Security
The Cortex-M7 offers optional ECC support for improved reliability on memories. It also supports additional cybersecurity features like cryptographic acceleration.
Performance and Clock Speed
Thanks to its microarchitecture enhancements, the Cortex-M7 achieves much greater performance than the Cortex-M4 at the same clock speed. The M4 can reach up to 150 DMIPS at 150 MHz, while the M7 can achieve 300 DMIPS at 300 MHz.
Power Consumption
Despite higher performance, the Cortex-M7 supports lower active power through advanced process nodes and energy-efficient design. However, static power may be higher than the Cortex-M4.
Cost and Area
The Cortex-M7 is built on smaller, more advanced process nodes down to 28nm. However it requires greater silicon area than the Cortex-M4, increasing chip costs. The M4 provides good performance with a smaller die footprint.
Cortex-M4 vs M7: Which Should You Choose?
For many embedded applications, the Cortex-M4 provides a good blend of performance, power efficiency and cost. With its solid DSP capabilities and real-time features, it can handle mid-range motor control, industrial sensing, automation, and IoT workloads.
For the most demanding embedded and microcontroller applications, the Cortex-M7 delivers top-tier performance thanks to its advanced microarchitecture. It excels at complex motor control systems, robotics, computer vision, machine learning inferencing, and high-speed communications.
So in summary, the Cortex-M4 is a very capable mid-range core providing good performance at lower cost and power. The Cortex-M7 is ARM’s high-end application processor for systems requiring the absolute highest performance and responsiveness.
