CM-Makefile: Makefile template for Cortex-M projects

Makefile template for ARM Cortex-M projects using the Arm GNU Toolchain. The template is meant to be included in project-specific Makefile.

See repository cm-makefile-examples for usage examples.

Dependencies

To successfully compile and debug the project, you need:

• Linux desktop (OS X should work as well)
• GCC ARM Embedded toolchain
• MCU vendor's HAL (start-up code, register definitions, ...)

Optional software:

• OpenOCD debugger
• Eclipse CDT Stand-alone Debugger
• Segger J-Link Software and Documentation Pack

Installation instructions are described in a separate file.

Usage

First, create Makefile. The Makefile should link to source files outside the project's source directory (such as libraries provided by the manufacturer) and include *.mk files from the CM-Makefile project. For example:

BIN = hello                     # Name of the output binary
SDK_DIR = ../mcu-vendor         # Target-specific library

INC = -I$(SDK_DIR)/inc
SRC_ASM = $(SDK_DIR)/src/startup.S
SCR_C = $(SDK_DIR)/src/system.c
SRC_LD = $(SDK_DIR)/target.ld

OPENOCD = openocd -f board/my_board.cfg

include cm-makefile/config.mk
include cm-makefile/openocd.mk  # For flash, debug and gdb targets
include cm-makefile/rules.mk

See the cm-makefile-examples repository for real-world examples.

Then simply run make to compile the project and make flash to upload it to the target.

The process will create .elf, .hex and .bin binaries in the build directory together with other files useful for debugging:

• .disasm: Disassembly output
• .sym: Name list (useful to check memory layout)
• .map: Linker map (useful to check linked object files, discarded sections, etc.)

To use a specific toolchain (other than the default arm-none-eabi), simply set the CROSS_COMPILE variable:

make CROSS_COMPILE=/usr/local/gcc-arm-none-eabi-4_9-2015q3/bin/arm-none-eabi-

Flashing and debugging

To flash the program into the target device, run make flash. To reset the CPU, run make reset.

Three different flasher implementations are provided:

• OpenOCD (openocd.mk)
• Black Magic Probe
• J-Link (jlink.mk)

To debug the project, run make gdb (which starts OpenOCD's GDB server) followed by make debug in a different terminal (which starts GDB in TUI mode).

It is also possible to use the Eclipse standalone debugger using make cdtdebug. The debugger has to be available as cdtdebug. If it isn't, simply change the CDTDEBUG variable.

J-Link and OpenOCD probes support make rtt which starts a RTT server. The RTT output can be captured using JLinkRTTClient or nc localhost 19021.

If needed, it is possible to provide a custom gdb executable by setting the GDB variable:

make GDB=/opt/arm-none-eabi-gdb-11.1/bin/arm-none-eabi-gdb debug

Configuration

The configuration is quite straightforward. Most of variables used in config.mk and rules.mk can be modified by the project-specific Makefile. For example:

• SRC_DIR: The main directory where source files are located (. by default)
• BUILD_DIR: The directory where object files and binaries are stored (./build by default)
• INC: Include path for header files (-I*.h) or linker scripts (-L*.ld)
• SRC_ASM: Assembly source files (*.S, *.s) outside the main SRC_DIR directory (e.g. target-specific startup code)
• SRC_C: C source files (*.c) outside the main SRC_DIR directory
• SRC_LD: Linker script (*.ld)
• DEF: Custom macros (-DMACRO equals to #define MACRO)
• ARCHFLAGS: CPU architecture (see below)
• FPFLAGS: FLoating point configuration (see below)
• WARNFLAGS: GCC warning options. You can define your own set of options or disable the unwanted ones by appending -Wno-* flags
• DBGFLAGS: GCC debugging options (-ggdb by defualt)
• OPTFLAGS: GCC optimization options (-O3 by defualt)
• PREPFLAGS: GCC preprocessor options (-MD -MP by defualt)
• STDFLAGS: GCC C dialect options (-std=gnu99 by default)
• CXXSTDFLAGS: GCC C++ dialect options (-std=gnu++11 by default)

Configuraiton specific to different debug probes

For openocd.mk:

• OPENOCD: OpenOCD command (with script selection) to set up debug session. You can use one of the built-in scripts or create your own.

For blackmagic.mk:

• BLACKMAGIC_PORT: Serial port to be used for the Black Magic Probe

For jlink.mk:

• JLINK_DEVICE: Target device (Cortex-M0 by default)
• JLINK_SPEED: Programming speed in Hz (1000 by default)

Configuration for a different target

CM-Makefile can be easily used with a different CPU core than the default Cortex-M0. It's only necessary to configure the ARCHFLAGS and FPFLAGS variables (FPFLAGS defaults to -mfloat-abi=soft):

CPU	ARCHFLAGS	FPFLAGS
Cortex-M0 (default)	-mcpu=cortex-m0	-mfloat-abi=soft
Cortex-M0+	-mcpu=cortex-m0plus	-mfloat-abi=soft
Cortex-3	-mcpu=cortex-m3	-mfloat-abi=soft
Cortex-M4 (Soft FP)	-mcpu=cortex-m4	-mfloat-abi=softfp -mfpu=fpv4-sp-d16
Cortex-M4 (Hard FP)	-mcpu=cortex-m4	-mfloat-abi=hard -mfpu=fpv4-sp-d16

License

CM-Makefile is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

See COPYING and COPYING.LESSER for details.