The GCC4MBED makefiles allow the use of the -j or --jobs makefile parameter when executing your project's makefile. This will allow multiple processes to be utilized for building your code and its dependencies. This will typically decrease the build time.
Example: make -j4 all
GCC4MBED supports the following rules when building your project makefile:
- help: Lists all rules, including device specific ones, that are supported by this makefile.
- all: The main rule for building your project and all of its official mbed dependencies.
- clean: Will clean out all of the output files for all targets listed in your makefile's DEVICE variable. This will cause a full rebuild when you next issue the all rule.
- clean-libs: Will clean out all of the output files for your USER_LIBS folders. This will cause a full rebuild of the user libraries when you next issue the all rule.
- clean-mbed: Will clean out all of the output files for the mbed SDK libraries. This will cause a full rebuild of the mbed SDK libraries when you next issue the all rule.
- clean-all: Cleans out all output files. Same as issuing clean, clean-libs, and clean-mbed rules.
- LPC1768-clean: Will clean out the LPC1768 output files for your project.
- DEVICE-clean: Will clean out the output files for the specified DEVICE (ie. KL25Z-clean, K64F-clean, NRF51_DK-clean, ...) from your project.
- deploy: Deploys the LPC1768 output binary to your device. Uses the GCC4MBED_DEPLOY environment variable to specify the commands for executing the copy operation. Refer to this link for more information about the GCC4MBED_DEPLOY variable.
- LPC1768-deploy: Same as deploy rule.
- DEVICE-deploy: Deploys the specified DEVICE's (ie. KL25Z-deploy, K64F-deploy, NRF51_DK-deploy, ...) output binary to your device.
The GCC4MBED project uses various makefile variables to configure and customize the binaries being built. This page describes these make variables.
The PROJECT variable is used in an application's makefile to indicate the name of the project being built. The output binaries with .elf, .bin, and .hex extensions will be given this as a name. The application's makefile must specify a value for this variable.
The GCC4MBED_DIR variable is used in an application's makefile to specify the root directory location of the GCC4MBED project. This directory will be the directory which contains the GCC4MBED install scripts such as win_install.cmd, linux_install, and mac_install. The application's makefile must specify a value for this variable.
The DEVICES variable is used in an application's makefile to specify a space delimited list of target devices for which the code should be built. Issuing a make help in your project's folder will list out all of the target devices that GCC4MBED currently knows about. This is a list of the targets mbed-os indicates have GCC_ARM toolchain support and currently (April 2017) this is a list of almost 200 different target devices. It should be noted that full test passes for GCC4MBED releases are restricted to the following targets:
- LPC1768
- K64F
- NRF51_DK
The default target device is LPC1768.
The SRC variable is used in an application's makefile to specify the root directory of the sources for this project. If not explicitly set by the application's makefile then it defaults to the directory in which the makefile is located. However it can be set to a different directory name if it happens that the project's source code is found in a different directory than the makefile.
The GCC4MBED_TYPE variable is used to specify the type of build to produce. It would typically be set as an environment variable but it can also be set in the application's makefile. The allowed values are:
- Debug - Build for debugging. Disables optimizations, enables asserts and other debug code, and doesn't allow the RTOS to put CPU into sleep mode. Best debugging experience but produces the largest code size.
- Release - Build for release. Optimizes for space, sets NDEBUG macro to disable asserts and other debug code, and allows the RTOS to put the CPU into sleep mode. Produces the smallest code size.
- Develop - The same as Release except that it doesn't set the NDEBUG macro and doesn't allow the RTOS to put the CPU into sleep mode. Produces code just a bit larger than Release because of additional debug/assert code.
The default value is Release.
MBED_OS_ENABLE is an optional variable that an application's makefile can set to 1 to cause the build to link with the full mbed-os library which includes RTOS support (mbed-os 5). Setting to 0 will link with the core mbed SDK library with no RTOS support (mbed 2).
It defaults to 1 to support the full featured mbed-os 5.
NEWLIB_NANO is an optional variable that an applications' makefile can set to 0, indicating that the standard newlib C library should be used instead of the smaller newlib-nano library. The user might want to do this if they need something like printf() for for 64-bit integers which isn't supported by newlib-nano.
It defaults to 1 so that the smaller newlib-nano library is used.
NO_FLOAT_SCANF is an optional variable that an application's makefile can set to 1 to indicate that scanf() does not need to support floating point values. This reduces code size.
It defaults to 0 so that floating point is supported in scanf().
NO_FLOAT_PRINTF is an optional variable that an application's makefile can set to 1 to indicate that printf() does not need to support floating point values. This reduces code size.
It defaults to 0 so that floating point is supported in printf().
DEFINES is an optional variable that can be used by an application's makefile to explicitly define some preprocessor macros that should be set when compiling the files for the main application. It doesn't get used for building the mbed SDK libraries.
USER_LIBS is an optional variable that an application's makefile can use to provide a space delimited list of folders containing user libraries to be compiled and linked into the application. Normally GCC4MBED will recurse into all subfolders within a user library folder to generate the include path for the library. If you proceed a folder name in the list with a '!' character then it will only add the root library folder to the include path. For example:
USER_LIBS := !../ros_lib_kinetic ../BufferedSerial ../Buffer
That example would just add the ../ros_lib_kinetic folder to the include path for the ROS library but it would recurse and add all subfolders found within ../BufferedSerial and ../Buffer. The makefile will always recurse and build any C/C++/ASM code found within a library folder, no matter if it has the '!' prefix or not.
The MBED_CONFIG_H variable is an optional variable which allows the user to specify the pathname of a header file containing custom mbed configuration parameters.
It defaults to using src/mbed_config.h
Note: Be careful when using this variable. If you are building multiple projects against the same instance of GCC4MBED, they must all use the same mbed_config.h since they will all share a single copy of the mbed library. It is also best to issue a make clean-all when changing this variable to make sure that the mbed library updates its header dependencies.
INCDIRS is an optional variable which can be used by an application's makefile to prepend a list of directories to the INCLUDE path used by the compiler for finding #included header files. This list should be space delimited.
Device_LSCRIPT is an optional variable which can be used to provide an override for the linker script to be used for a particular device. For example, setting LPC1768_LSCRIPT := lpc1768custom.ld will cause the linker to use lpc1768custom.ld instead of the one provided by the mbed SDK when building for the LPC1768 target.
LIBS_PREFIX is an optional variable that an application's makefile can use to specify a list of libraries that should be linked into its final binary before it links in the mbed SDK libraries.
LIBS_SUFFIX is an optional variable that an application's makefile can use to specify a list of libraries that should be linked into its final binary after it links in the mbed SDK libraries.
GPFLAGS is an optional variable that an application's makefile can use to specify additional flags for compiling C++ source files.
GCFLAGS is an optional variable that an application's makefile can use to specify additional flags for compiling C source files.
GAFLAGS is an optional variable that an application's makefile can use to specify additional flags for assembling .s assembly language source files.
OPTIMIZATION is an optional variable that an application's makefile can set to s, g, 0, 1, 2, or 3 for overriding the compiler's optimization level. It defaults to s (size optimization) for Develop and Release builds and is set to 0 (optimizations disabled) for Debug builds. This optimization is only used for the application's code itself and the mbed libraries are always built with the default for the specified GCC4MBED_TYPE.
GCC4MBED_TOOLPATH is an optional path to where the GNU tools are located.
It defaults to $(GCC4MBED_DIR)/gcc-arm-none-eabi/bin
EXCLUDE is an optional variable than an application's makefile can use to specify a pattern for excluding files from the SRC folder tree. This variable is a space-separated list of patterns to exclude from the build.
VERBOSE is an optional variable that an application's makefile can set to 1, indicating that all build tool commands should be displayed to the user. For example this will cause the full GCC command line for each source file to be shown.
MRI is a library that can be linked into your application to provide debug monitoring capabilities. This allows GDB, the GNU Debugger, to connect to your device via a serial port. It enables the use of breakpoints, data watchpoints, single-stepping, inspection/modification of variables, etc.
Note: Currently the MRI debug monitor is only supported on LPC1768, LPC4330_M4, and NUCLEO_F429ZI targets. It will automatically be disabled for other device targets.
The MRI_ENABLE variable is set to 1 to enable the MRI debug monitor to be linked into the executable for devices that MRI supports.
Defaults to 0.
The MRI_BREAK_ON_INIT variable can be set in an application's makefile to a non-zero value to indicate that the MRI debugger should halt and wait for GDB to attach before executing the global constructors and the main() function. This allows the developer to set breakpoints in areas of interest before the main code starts executing.
The default value for this variable is 1 and is ignored when MRI_ENABLE = 0.
The MRI_SEMIHOST_STDIO variable can be set in an application's makefile to a non-zero value to allow the debug monitor to use semi-host calls to redirect stdin/stdout/stderr to GDB's console.
The default value for this variable is 1 when MRI_ENABLE is set to 1.
The MRI_UART is an optional variable that can be set in an application's makefile to configure the device's UART being used for communicating between GDB and MRI. The allowed values will depend on the target but the following are examples supported by the LPC1768 target:
| MRI_UART_MBED_USB |
| MRI_UART_MBED_P9_P10 |
| MRI_UART_MBED_P13_P14 |
| MRI_UART_MBED_P28_P27 |
It defaults to MRI_UART_MBED_USB if not explicitly set in the application's makefile.
By default the auto-baud functionality is used to allow the device to automatically detect the baud rate used by GDB when it first connects. However it is possible to configure a fixed baud rate by appending a MRI_UART_BAUD=baudRate specifier to the MRI_UART variable string. An example:
MRI_UART := "MRI_UART_MBED_USB MRI_UART_BAUD=115200"
PROJECT := HelloWorld
DEVICES := LPC1768
GCC4MBED_DIR := ../..
NO_FLOAT_SCANF := 1
NO_FLOAT_PRINTF := 1
include $(GCC4MBED_DIR)/build/gcc4mbed.mk