The gate count refers to the number of logic gates present on a microcontroller or processor chip. It gives an indication of the complexity and capabilities of the chip. For the Arm Cortex-M series of microcontrollers, the gate count varies across different variants in the product family.
Cortex-M0 and Cortex-M0+
The Cortex-M0 and Cortex-M0+ are Arm’s most compact and energy efficient microcontrollers based on the Arm v6-M architecture. They are designed for simple, low-cost applications where memory footprint and power consumption need to be minimized.
The Cortex-M0 has approximately 12,000 gates while the Cortex-M0+ has approximately 15,000 gates. The modest gate counts allow the chips to deliver excellent performance per MHz, making them well-suited for low-power IoT edge nodes and simple controls tasks.
Cortex-M1
The Cortex-M1 microcontroller has a gate count of approximately 30,000 gates. It builds on the Cortex-M0/M0+ foundation by adding more advanced features like improved single-cycle multiplier, bit-banding, and micro-trace buffer.
The increased gate count provides better performance while retaining high energy efficiency. The Cortex-M1 is positioned for applications like home appliances, smart meters, human interface devices, etc. that demand more processing capabilities.
Cortex-M3
The Cortex-M3 is an extremely popular microcontroller known for its optimal balance between performance and power. It has a gate count of approximately 100,000 gates.
The substantially higher gate count compared to Cortex-M0/M0+ enables advanced capabilities like memory protection unit, nested vectored interrupt controller, low-latency interrupt handling and optional floating point unit. This makes the Cortex-M3 suitable for applications like motor control, industrial automation, robotics, etc.
Cortex-M4
The Cortex-M4 builds on the Cortex-M3 design by incorporating a floating point unit and DSP instructions as standard features. It has a gate count of approximately 150,000 gates.
The increased gate count delivers significantly improved digital signal processing performance. With extensive DSP and math capabilities, the Cortex-M4 finds use in applications like digital audio processing, control systems, image processing, computer vision, machine learning inferencing, etc.
Cortex-M7
The Cortex-M7 represents Arm’s highest performance Cortex-M series microcontroller. It features a high-speed dual-issue pipeline and superscalar architecture. The Cortex-M7 gate count is approximately 300,000 gates.
The robust gate count provides capabilities like application-level cache, optional L1 data and instruction cache, ECC protected memory, SIMD instructions, optional MPU, etc. This makes the Cortex-M7 suitable for very demanding embedded applications in automotive ADAS, industrial control, robotics, etc.
Cortex-M23 and Cortex-M33
The Cortex-M23 and Cortex-M33 are secure microcontrollers built on the Arm v8-M architecture. They incorporate security features like Arm TrustZone and a cryptographic acceleration unit.
The Cortex-M23 has a gate count of around 90,000 gates while the Cortex-M33 has around 150,000 gates. The higher gate count of Cortex-M33 enables more advanced capabilities. Both microcontrollers are designed for security-critical embedded applications.
Factors Affecting Gate Count
The gate count depends on various design factors and implementation choices made by Arm and silicon partners. Some of the key factors are:
- Core architecture – More advanced architectures like superscalar pipelines require higher gate counts.
- Presence of additional units – Units like floating point unit, caches, cryptography block etc. increase gate count.
- Process node – Fabricating the design on a smaller process node like 40nm or 28nm reduces gate count versus older 90nm nodes.
- Design libraries – Use of standard cell libraries optimized for area can reduce gate count versus libraries optimized for speed/power.
- Level of integration – Integration of more peripheral interfaces and mixed signal blocks in addition to the core increases overall gate count.
- Level of customization – Gate count tends to increase when significant modifications are made to the core design.
Tradeoffs in Gate Count
The optimal gate count depends on the target application requirements and involves design tradeoffs between factors like:
- Performance – More gates can potentially enable higher speed and throughput.
- Power – Lower gate counts reduce switching power dissipation.
- Area/cost – Higher gate count increases silicon area which raises costs.
- Features – Additional capabilities usually need more logic gates.
- Flexibility – Gate count limits customization options in some cases.
- Verification complexity – More gates make functional verification more difficult.
Finding the optimal balance between these factors is key to maximizing the value delivered by the microcontroller for a given application space.
Trends in Cortex-M Gate Counts
Some notable trends seen in the evolution of Cortex-M series gate counts are:
- Gradual increase from 12K gates in Cortex-M0 to 300K gates in Cortex-M7 showing greater integration over time.
- Larger jumps in gate count when new architectural capabilities are introduced – for example, between Cortex-M3 and Cortex-M4.
- Constant gate count reduction at same architecture node through smaller process nodes – for example 150K gates for Cortex-M3 at 90nm versus 100K gates at 40nm.
- Introduction of specialized low gate count variants for simple applications – Cortex-M0/M0+, Cortex-M23.
- Higher gate counts for versions targeting security applications – Cortex-M23 and Cortex-M33.
Overall, the gate count tends to progressively increase over time as new features and architectural optimizations are incorporated by Arm into the Cortex-M family. But the high configurability ensures minimal overhead for any specific application.
Conclusion
In summary, the gate count of Cortex-M microcontrollers ranges from around 12K gates for Cortex-M0 to around 300K gates for Cortex-M7. Lower gate count variants like Cortex-M0 cater to simple and extremely power sensitive applications. Higher gate count versions like Cortex-M7 enable very high performance capabilities required by complex embedded systems.
The optimal gate count depends on the tradeoffs between performance, power, area, features and other factors for the target application. Arm and its partners have introduced several Cortex-M variants to service the diverse needs of embedded systems across automotive, industrial, consumer and enterprise market segments.
