Dean Camera
9 years ago
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DMBS - Dean's Makefile Build System
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===================================
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Writing Your Own Modules
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------------------------
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A DMBS module consists of the several boilerplate sections, explained below.
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## The DMBS module hooks
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Your module needs to advertise to DMBS its name, its makefile targets, the
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required and optional variables, and the variables and macros the module
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provides for use elsewhere. This is achieved with the following section:
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DMBS_BUILD_MODULES += EXAMPLE
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DMBS_BUILD_TARGETS += example-target another-target
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DMBS_BUILD_MANDATORY_VARS += MANDATORY_NAME ALSO_MANDATORY
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DMBS_BUILD_OPTIONAL_VARS += OPTIONAL_NAME ALSO_OPTIONAL
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DMBS_BUILD_PROVIDED_VARS += MEANING_OF_LIFE
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DMBS_BUILD_PROVIDED_MACROS += STRIP_WHITESPACE
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The example above declares that this module is called `EXAMPLE`, and exposes the
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listed targets, variable requirements and provides variables and macros.
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Your module name and provided variable/macro names must be unique, however you
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can (and should) re-use variable names where appropriate if they apply to
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several modules (such as `ARCH` to specify the project's microcontroller
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architecture). Re-using targets is not recommended, but can be used to extend
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the dependencies of another module's targets.
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## Importing the CORE module
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Next, your module should always import the DMBS `CORE` module, via the
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following:
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# Conditionally import the CORE module of DMBS if it is not already imported
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DMBS_MODULE_PATH := $(patsubst %/,%,$(dir $(lastword $(MAKEFILE_LIST))))
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ifeq ($(findstring CORE, $(DMBS_BUILD_MODULES)),)
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include $(DMBS_MODULE_PATH)/core.mk
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endif
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This ensures that the `make help` target is always available. In addition, the
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`CORE` module exposes some [commonly used macros and variables](core.md) to
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your module.
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## Setting optional variable's defaults
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If a variable is optional, you should provide a default value. Do this via the
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`?=` operator of `make`, which sets a variable's value if it has not yet been
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set:
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MY_OPTIONAL_VARIABLE ?= some_default_value
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## Sanity checking user input
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Sanity checks are what make DMBS useful. Where possible, validate user input and
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convert generated errors to human-friendly messages. This can be achieved by
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enforcing that all the declared module mandatory variables have been set by the
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user:
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# Sanity-check values of mandatory user-supplied variables
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$(foreach MANDATORY_VAR, $(DMBS_BUILD_MANDATORY_VARS), $(call ERROR_IF_UNSET, $(MANDATORY_VAR)))
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As well as complaining if they are set, but currently empty:
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$(call ERROR_IF_EMPTY, SOME_MANDATORY_VARIABLE)
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$(call ERROR_IF_EMPTY, SOME_OPTIONAL_BUT_NON_EMPTY_VARIABLE)
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Or even if they are boolean (`Y` or `N`) variables that have an invalid value:
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$(call ERROR_IF_NONBOOL, SOME_BOOL_VARIABLE)
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## Adding targets
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The meat of a DMBS module is the targets, which are run when the user types
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`make {target name}` from the command line. These can be as complex or simple
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as you like. See the GNU make manual for information on writing make targets.
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example-target:
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echo "Your DMBS module works!"
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## And finally, list the PHONYs
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Important in GNU Make is the concept of phony targets; this special directive
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tells make that a given target should never be considered a valid file. Listing
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phonies ensures that, for example, if your module had a target called `build`,
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it would always run when the user types `make build` from the command line, even
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if a file called `build` existed in the user project folder.
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You can list module-internal targets here, as well as mark all public targets
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via the module header's `DMBS_BUILD_TARGETS` variable.
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# Phony build targets for this module
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.PHONY: $(DMBS_BUILD_TARGETS) some-module-internal-target another-internal-target
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