How to Start with Cortex-M1

The Cortex-M1 processor from ARM is a great choice for starting with ARM microcontroller development. The Cortex-M1 offers a good balance of performance, power efficiency and ease of use. Here is a step-by-step guide on how to get started with the Cortex-M1 processor.

1. Learn About the Cortex-M1 Architecture

Before diving into development, it helps to understand the key features and architectural details of the Cortex-M1 processor. Some key things to learn about include:

• ARMv6-M architecture – Cortex-M1 implements the ARMv6-M architecture which is optimized for microcontroller applications.
• 3-stage pipeline – Simple 3-stage pipeline allows efficient instruction execution while minimizing power consumption.
• Thumb instruction set – Only supports the Thumb 16-bit compressed instruction set for improved code density.
• Nested Vectored Interrupt Controller (NVIC) – Handles interrupts and exceptions in hardware.
• SysTick timer – 24-bit system timer for creating periodic interrupts.
• Memory protection unit – Optional memory protection features for safety critical applications.
• Debug interface – Supports debugging via SWD and JTAG interfaces.

Read the technical reference manual and other resources to get familiar with the architecture and capabilities of the processor.

2. Obtain a Development Board

To start actual hands-on development and programming, you will need a development board or kit that contains a Cortex-M1 processor and the necessary peripherals and I/O interfaces. Some options to consider:

• STM32VLDISCOVERY – Discovery kit with STM32F100RBT6 MCU featuring Cortex-M1 core.
• NXP LPC1114FN28 – Low-cost LPC1114 MCU based on Cortex-M1.
• TI Stellaris Launchpad – Some Launchpad boards use Cortex-M1-based MCUs like LM3S811.

Make sure to get a board that provides options for interfacing with peripheral devices for input/output. Many kits include add-on boards or Arduino-compatible headers for easy interfacing.

3. Set Up Development Tools

You will need a development toolchain to write, compile and debug code for the Cortex-M1 processor. Some options to consider:

• GCC – Open-source compiler and toolchain that supports Cortex-M1.
• Keil MDK-ARM – Popular commercial IDE and toolchain for ARM processors.
• IAR Embedded Workbench – Commercial IDE and toolchain specifically optimized for ARM cores.

You may need to download the correct version or packages for the specific Cortex-M1 device you are using. The toolchain vendor or device provider should have specific instructions.

4. Start with Sample Code

Most development kits and MCU providers offer sample code and tutorials to help kickstart Cortex-M1 development. Some options to try:

• Blink an LED – Simplest program to test the toolchain.
• Button debouncing – Read inputs and debounce the switch press in code.
• PWM LED fading – Use a timer peripheral to fade an LED.
• UART serial port – Communicate over the serial port with a PC.

Starting with the simplest sample code helps confirm your development environment is set up correctly before moving on to more complex projects.

5. Learn Startup and Runtime Initialization

Understanding the processor and runtime startup process is important for any embedded development:

• Boot sequence – The steps the microcontroller takes from reset to main().
• Linker scripts – Configures memory regions and locations for code and data.
• Startup code – C runtime and processor/peripheral initialization code.
• Interrupts and vectors – How interrupt handlers are registered and called.
• Clock configuration – Setting up internal PLLs and oscillators.

Go through your toolchain and board specific initialization code thoroughly and understand what is happening behind the scenes before main().

6. Learn GPIO and Peripheral Control

Interfacing with sensors, actuators and other devices involve GPIO and peripheral control. Key concepts include:

• GPIO ports and pins – Enable clocks, set pin modes and read/write.
• Alternate functions – Assign pins for peripheral interfaces like I2C, SPI, UART.
• Device registers – Read and write to memory-mapped peripheral registers.
• Interrupts – Handling peripheral interrupts on GPIOs and other devices.
• Bit-banding – Atomic bit set/clear operations.
• Bit manipulation – Common bit operations like set, clear, toggle, mask, etc.

Start with simple interfaces like digital input/output, then move on to serial protocols before tackling more complex peripherals.

7. Explore Power Management Features

Optimizing power consumption is important for many embedded applications. Cortex-M1 and ARMv6-M provide various power management capabilities:

• Sleep modes – Different low power modes for CPU, peripherals and clocks.
• Wakeup sources – GPIO pins, interrupts or events to wakeup from sleep.
• Clock gating – Disable unused peripheral clocks to save power.
• Tickless idle – Stop SysTick timer in idle for low power waiting.
• Voltage scaling – Lower voltages to reduce power when high performance is not required.

Measure and profile power usage using different configurations and techniques to squeeze every drop of efficiency out of the design.

8. Use a RTOS

A Real-Time Operating System (RTOS) provides task scheduling and resource management capabilities. An RTOS can simplify more complex projects.

Some RTOS options for Cortex-M1:

• FreeRTOS – Popular free and open RTOS that supports Cortex-M.
• Mbed OS – Mbed framework includes an RTOS optimized for Cortex-M.
• Micrium uC/OS – Commercial RTOS optimized for ARM cores.
• TI-RTOS – RTOS from Texas Instruments for their ARM MCUs.

Start by creating simple RTOS threads for processing, input handling and output control. An RTOS makes it easy to divide an application into logical blocks.

9. Debugging Tips and Tricks

Debugging on embedded devices requires some unique techniques:

• Enable debug peripherals – SWD, ETM, ITM, etc.
• Watch variables – Add key variables to the watch window.
• Breakpoints – Strategically set code breakpoints.
• Step through code – Methodically step through instructions.
• Memory inspection – Look at RAM and flash contents.
• Trace using printf – Simple but effective debugging output.

Having robust debugging capability via JTAG/SWD and on-chip trace features enables analyzing and troubleshooting code easily.

10. Learn ARM Assembly Basics

Having a basic grasp of ARM assembly is useful for debugging, optimization and understanding code generation. Some tips:

• GCC flags – Use compiler flags like -S to generate assembly output.
• Assembler syntax – Learn the ARM register and assembly syntax.
• Instructions – Understand common ARM Thumb and ARM instructions.
• Registers – Purpose of R0-R12, SP, LR, PC.
• Disassembly – Step through compiled assembly instructions.

Start by examining small simple functions in assembly, and then work your way up to more complex pieces of code.