The main practical differences between the Arm Cortex-M0 and Cortex-M3 for C programmers come down to performance, features, and toolchain support. The Cortex-M3 is faster, supports more advanced features like memory protection units, and has better toolchain support overall. However, the Cortex-M0 is cheaper and may be suitable for simpler applications where performance is less critical.
Performance
The Cortex-M3 runs significantly faster than the Cortex-M0 – it can typically run at 50-100 MHz compared to 25-50 MHz for the M0. The M3 has a 3-stage pipeline compared to the 2-stage pipeline in the M0, allowing for greater instruction-level parallelism. It also includes microarchitectural features like branch prediction and caches that improve real-world performance.
For most C programs, this means code will execute faster on the M3. Benchmarks show the M3 achieves 1.7x to over 2x higher Dhrystone MIPS compared to the M0 at a given clock speed. For time-critical C code, especially involving tight loops, the M3’s higher performance can make a significant difference.
Features
The Cortex-M3 includes a number of features not present on the M0 that can benefit C programmers:
- Memory Protection Unit – hardware support for protecting regions of memory from access violations.
- Nested Vectored Interrupt Controller – allows priority assignment for interrupts.
- Wake-up Interrupt Controller – allows wake up from sleep/low power on select interrupts.
- Single Cycle I/O Port – improves GPIO performance.
- Bit-Banding – provides atomic bit-manipulation addressing.
These features give C developers more hardware capabilities to leverage in their code for security, reliability, power savings, and performance.
Toolchain Support
As the more widely used core, the Cortex-M3 generally has better toolchain support in both commercial and open-source toolchains:
- GCC – the Arm Embedded GCC toolchain has Cortex-M3 ports dating back to GCC 4.5+ with robust support. Cortex-M0 support did not appear until GCC 5.0.
- LLVM – the LLVM project provides solid support for Cortex-M3 back to LLVM 3.3. Cortex-M0 support is again more recent.
- IAR/Keil/ARM Compiler – commercial toolchains uniformly provide excellent support for Cortex-M3, while Cortex-M0 support varies.
The Cortex-M3’s longer time on the market means toolchain vendors have had more time to mature its support. More extensive testing and optimization is evident when comparing code generation, libraries, and other factors. For teams relying on commercial compilers especially, this can simplify development.
Peripheral Support
Both M0 and M3 parts support integration of Arm peripherals like GPIO, timers, communication interfaces, etc. However, Cortex-M3 chips tend to integrate more advanced peripherals that benefit C developers. Common examples include:
- Ethernet MAC – permits high-speed networking from C code.
- USB OTG – allows implementing USB hosts or devices in C.
- Cryptographic Accelerators – offloads cryptographic work from main CPU.
- LCD Controllers – generates analog LCD waveforms.
- CAN Controllers – provides Controller Area Network communication.
The greater CPU performance of the M3 makes it more suitable for leveraging advanced integrated peripherals in cases where an M0 might struggle.
Power Management
While the Cortex-M0 has basic power management features like sleep modes and wait-for-interrupt instructions, the Cortex-M3 adds more advanced capabilities:
- Dynamic Voltage Scaling – allows scaling CPU voltage/frequency during operation.
- Wake-up Interrupt Controller – enables wake on selected interrupts.
For low-power applications written in C, an M3 microcontroller enables implementing more aggressive power saving strategies with faster wake-up response.
Physical Size
The Cortex-M0 is among the smallest Arm cores, with implementations under 16kB of total code size. The M3 is moderately larger at around 20-40kB. While not a major factor, the smaller size can benefit C developers working on extremely compact microcontroller designs.
Cost
Due to its simplicity, the Cortex-M0 is generally cheaper to manufacture and implement in microcontroller chips. The lower cost opens it up to very high-volume, cost-sensitive products that can leverage C programming.
Conclusion
For C developers, the Cortex-M3 represents a “sweet spot” providing high performance, advanced features, robust toolchain support, peripheral integration, and power management. The M0 trades these advantages for reduced cost and size – making it suitable for simple C applications where performance is not critical. Most C programmers will gain the most benefit from the M3 overall, but the M0 has its place for less demanding use cases.
