Cortex-M0 and Cortex-M1 are two different microcontroller cores designed by ARM for low-power embedded applications. The main differences between Cortex-M0 and Cortex-M1 are:
- Architecture: Cortex-M0 has a 3-stage pipeline while Cortex-M1 has a dual-issue pipeline with speculative execution
- Performance: Cortex-M1 offers significantly higher performance compared to Cortex-M0
- Memory Protection Unit: Cortex-M1 includes an MPU while Cortex-M0 does not have an MPU
- Debug Support: Cortex-M1 offers more advanced debug support features
- DSP Instructions: Cortex-M1 supports DSP instructions but Cortex-M0 does not
- Power Consumption: Cortex-M0 is more power efficient for very low power applications
- Cost: Cortex-M0 is lower cost while Cortex-M1 provides higher performance at a higher cost
Architecture
The Cortex-M0 CPU core has a simple 3-stage pipeline consisting of Fetch, Decode and Execute stages. It is an in-order execution pipeline without any branch prediction or speculative execution capabilities. The simple pipeline allows Cortex-M0 to be very energy efficient but it limits performance.
On the other hand, Cortex-M1 implements a dual-issue superscalar pipeline with speculative execution. It can fetch and decode two instructions per clock cycle. The pipeline has Fetch, Decode, Execute, Memory access and Writeback stages. Speculative execution with branch prediction enables much higher performance compared to the simple Cortex-M0 pipeline.
Performance
The dual-issue pipeline with speculative execution gives Cortex-M1 significantly higher performance than Cortex-M0. Cortex-M1 delivers 1.25 DMIPS/MHz while Cortex-M0 can do only 0.9 DMIPS/MHz. So at equivalent clock frequencies, Cortex-M1 provides up to 38% higher performance.
In real applications, the difference can be even higher depending on the code. The speculative execution and dual-issue capabilities reduce stalls in the Cortex-M1 pipeline, allowing more instruction-level parallelism. So Cortex-M1 can execute most code much faster than Cortex-M0.
Memory Protection Unit
Cortex-M1 includes an optional Memory Protection Unit (MPU) while Cortex-M0 does not have a MPU. The MPU provides support for protected memory regions and split address spaces in Cortex-M1 based microcontrollers.
The MPU allows creating isolated and protected memory regions for different programs and tasks in a Cortex-M1 system. This improves reliability and security especially in more complex embedded systems. Cortex-M0 lacks this memory protection feature.
Debug Support
Cortex-M1 provides more advanced debug and trace support capabilities compared to Cortex-M0. Key features only supported by Cortex-M1 include:
- Instruction address matching for breakpoints
- Data value matching for watchpoints
- Trace Port Interface Unit (TPIU) for streaming trace
- Instrumentation Trace Macrocell (ITM) for printf-style debugging
These debug features help with analyzing system behavior, profiling code, and tracing execution flows in complex Cortex-M1 applications. Cortex-M0 has basic breakpoint debug capability but lacks advanced real-time trace features.
DSP Instructions
The Cortex-M1 instruction set includes optional DSP extensions like single-cycle MAC operations for signal processing applications. This allows efficient digital filtering, FFTs, and other DSP algorithms on Cortex-M1 cores.
In contrast, Cortex-M0 does not support any DSP instructions. DSP algorithms have to be implemented using regular instructions on Cortex-M0, which is less efficient in terms of performance and power.
Power Consumption
Cortex-M0 is designed to be extremely power efficient and is aimed at ultra low power embedded applications. It can operate at under 25 μA/MHz in typical silicon process nodes.
Cortex-M1 offers higher performance at the cost of slightly higher power consumption. It can operate at around 100 μA/MHz in 40nm process. So for very low power sensor nodes and energy harvesting applications, Cortex-M0 may be better suited.
Cost
The simple 3-stage pipeline of Cortex-M0 results in a smaller silicon area and lower cost implementation compared to the more complex Cortex-M1 pipeline. Cortex-M0 based MCUs will usually be lower cost.
But Cortex-M1 delivers much higher performance per dollar despite the higher cost. So for applications that need higher performance with reasonable cost and power constraints, Cortex-M1 is better suited than Cortex-M0.
Use Cases
Here are some example use cases where Cortex-M0 or Cortex-M1 may be more suitable:
- Cortex-M0 – Extremely power constrained devices like hearing aid, wireless sensor nodes, wearables
- Cortex-M0 – Cost sensitive control applications like remote controls, motor controls
- Cortex-M1 – Low power motor control, industrial control systems
- Cortex-M1 – Networking equipment, WiFi/Bluetooth SoCs, routers
- Cortex-M1 – Digital signal processing, audio/voice applications
Cortex-M0 Example MCUs
Some example microcontrollers based on the Cortex-M0 core include:
- STM32L0 from STMicroelectronics
- EFM32 Gecko from Silicon Labs
- SAM L10/L11 from Microchip (Atmel)
- NXP LPC800 series
- Cypress PSoC 4000S / 4100S / 4100S+
Cortex-M1 Example MCUs
Some example microcontrollers based on the Cortex-M1 core include:
- STM32F1 from STMicroelectronics
- EFM32 Wonder Gecko from Silicon Labs
- NXP LPC1700 series
- Cypress PSoC 5
- Infineon XMC1100 series
Conclusion
In summary, Cortex-M1 is suitable for embedded systems that need higher performance with low power constraints, while Cortex-M0 targets extremely low power or cost sensitive applications that can compromise on performance. Cortex-M1 also provides more advanced features for memory protection, debugging and DSP which enable more complex system use cases.
It is important to evaluate both technical and commercial requirements like performance, power, cost, and features when selecting between Cortex-M0 and Cortex-M1 for an embedded system design.
