Arm Cortex-M

Introduction

ARM is the dominant processor architecture in mobile and embedded devices. The CPU architectures are developed by ARM Ltd. and licensed by various hardware manufacturers for use in processor design. Plenty of ARM-based processor models are available on the market, ranging from special-purpose microcontrollers to generic computing with support for consumer operating systems. The price-performance ratio and broad availability makes ARM processors ideal for use in hobbyist electronics projects.

History

The initial ARM processor architecture was developed in the mid-1980s by the British computer manufacturer Acorn Computers with the goal of creating an auxiliary processor for a business computer product. The acronym ARM stands for Acorn RISC Machine. ARM Ltd. was founded as a joint venture with the U.S. computer manufacturer Apple with the goal of developing an improved architecture that could be used for the main processor of a computer.

Cross-Compiling

If your operating system is Ubuntu Linux, running on an x64/AMD64 processor, you need the following package to cross-compile code to run on ARM Cortex series processors:

sudo apt-get install gcc-arm-none-eabi

CMSIS

Arm specifies a standard C interface for programming Cortex-M processors, the Cortex-M Standard Interface (CMSIS). The Arm licensees are strongly encouraged to provide the CMSIS functions as part of their microcontroller programming SDK. Third-party software libraries usually rely on CMSIS availability.

Intrinsic Functions

Functions that generate instructions not provided by ISO/IEC C

Instruction	CMSIS intrinsic function
CPSIE I	void __enable_irq(void)
CPSID I	void __disable_irq(void)
ISB	void __ISB(void)
DSB	void __DSB(void)
DMB	void __DMB(void)
NOP	void __NOP(void)
REV	uint32_t __REV(uint32_t int value)
REV16	uint32_t __REV16(uint32_t int value)
REVSH	uint32_t __REVSH(uint32_t int value)
SEV	void __SEV(void)
WFE	void __WFE(void)
WFI	void __WFI(void)

Functions for accessing special registers

Register	CMSIS read function	CMSIS write function
PRIMASK	uint32_t __get_PRIMASK (void)	void __set_PRIMASK (uint32_t value)
CONTROL	uint32_t __get_CONTROL (void)	void __set_CONTROL (uint32_t value)
MSP	uint32_t __get_MSP (void)	void __set_MSP (uint32_t TopOfMainStack)
PSP	uint32_t __get_PSP (void)	void __set_PSP (uint32_t TopOfProcStack)

Microcontrollers

ARM's family of Cortex-M processors (notably M0, M0+, M3, M4) are designed for use as energy-efficient microcontrollers, where M0+ is the cheapest and most efficient, and M4 is the fastest and most capable (offering DSP functions and a floating point unit).

Reference Manuals

• CMSIS abstraction layer for programming Cortex-M processors

Cortex-M0+

• Generic User Guide
• ARMv6-M Architecture Reference Manual

Cortex-M4

• Generic User Guide
• ARMv7-M Architecture Reference Manual

Development Boards

• Nucleo boards by STMicroelectronics, with STM32 processors
  • Sold by: DigiKey, Reichelt, Conrad, etc.
• Freedom boards by NXP (after buying Freescale), with Kinetis processors
• LPCXpresso boards by NXP
• ARM related products by Olimex

Software Development Tools

• ARM Mbed framework that provides higher-level C++ API, with downloadable or web-based IDE.
• GNU ARM Embedded Toolchain for Ubuntu
  or the latest toolchain for all Linux distros, macOS, and Windows directly from ARM Ltd.
• GNU MCU Eclipse plugin with good support for STM32
• OpenOCD on-chip debugger
• STM32Cube tools and drivers package for STM32 programming (CMSIS and HAL libraries)
• LPCXpresso IDE and utility programs for programming LPCXpresso boards.

Tutorials

• Arm Cortex-M Assembly programming
• Programming the STM Nucleo-64 boards
• Programming the STM Nucleo-32 boards
• Programming the Cortex-M4 development board SAM E54 Xplained Pro
• ARM Bootloader
• ARM GCC Inline Assembler Cookbook by Harald Kipp
• Collection of Cortex-M tutorials by Keil
• Programming STM32F103RET Cortex-M3 with GNU ARM Eclipse Plugin