The Cortex-M1 and Cortex-M3 are both ARM processor cores designed for microcontroller applications. The main differences between them come down to architecture, performance, features, and intended use cases.
Architecture
The Cortex-M1 has a 3-stage pipeline, while the Cortex-M3 has a deeper 5-stage pipeline. This allows the M3 to potentially execute more instructions per clock cycle. The M1 is based on the ARMv6-M architecture, while the M3 uses the newer ARMv7-M architecture with Thumb-2 instruction set. This provides performance improvements and additional instructions over the original Thumb ISA used by the M1.
Performance
The M3 is the higher performance core, capable of clock speeds up to 300 MHz while the M1 tops out around 200 MHz. Some specific performance differences:
- Higher DMIPS/MHz rating for the M3 (1.25 vs 0.9)
- Faster branch prediction on the M3
- Optional double-precision FPU on M3, only single-precision on M1
- More advanced memory architecture – M3 has multi-layer AHB bus matrix, M1 has simpler bus topology
In general, the M3 should be about 2-3x faster clock-for-clock vs the older M1.
Features
The M3 includes a number of features lacking on the M1:
- Memory Protection Unit for added security
- Nested Vectored Interrupt Controller
- Optional SIMD instructions
- Low power sleep modes
- Bit-banding for atomic bit manipulation
- Single-cycle multiplier
The M3 builds on the M1 foundation by adding advanced features suited for modern embedded applications. This makes it easier to achieve better performance and determinism.
Intended Use Cases
The Cortex-M1 is aimed at basic microcontroller applications that demand high efficiency but do not require high performance. Some example applications include:
- Simple home appliances
- Toys
- Low-end motor controllers
The Cortex-M3 is targeted toward more advanced and demanding applications such as:
- Industrial automation
- Automotive systems
- Networking equipment
- Motor control
- Digital power supplies
- Medical devices
The M3 is well suited for applications that need low latency, real-time responsiveness, and digital signal processing capabilities.
Development Tools and Support
Both the Cortex-M1 and M3 are supported by ARM’s Keil and DS-5 Development Studio IDEs. There is wider commercial support and more mature software development tools for the M3 given its more recent vintage and high adoption in the marketplace.
Example Devices and SoCs
Some example microcontrollers and SoCs based on each core:
- Cortex-M1: NXP LPC1111, Atmel SAM D20, TI MSP432P401R
- Cortex-M3: STM32 F103, NXP LPC1768, Atmel SAM 3X, TI TM4C123
The Cortex-M3 is used much more extensively in silicon devices compared to the now obsolete M1.
Power Consumption
Despite its higher performance, the Cortex-M3 can actually be more power efficient in active and sleep modes than the older M1 core. Static power may be slightly higher on the M3 but its advanced sleep modes help make up for this.
Some key differences in power consumption:
- 0.77 mW/MHz for M3 vs 1.8 mW/MHz for M1 (active power)
- 61 μW/MHz for M3 vs 200 μW/MHz for M1 (sleep mode)
The M3 benefits from being implemented on a smaller process node (90nm initially) than the M1 (130nm).
Development Cost
The Cortex-M3 requires external flash for storage rather than on-chip embedded flash like some M1 chips. This can make developing for the M3 slightly more expensive since external flash and debugging hardware may be needed.
However, the M3’s superior performance, larger software ecosystem, and abundance of low cost development boards available help offset the higher hardware costs compared to the minimalist M1.
Summary and Conclusion
In summary, the Cortex-M3 is the clear winner compared to the aging Cortex-M1 in almost every respect:
- Higher performance from advanced 5-stage pipeline
- More features like memory protection, nested interrupts
- Lower power – uses less active and sleep current
- Greater software and tool support due to popularity
The only advantages for the M1 are marginally lower static power draw and potentially lower system costs. But the M3 more than makes up for this with its substantially better performance and features.
For new 32-bit ARM microcontroller designs, the Cortex-M3 is certainly the superior choice vs the obsolete Cortex-M1. There is a reason why the M1 has been replaced while the M3 lives on in silicon chips today. The Cortex-M3 architecture provides the right blend of high performance, low power, and advanced features needed for modern embedded systems.
