BSP and Device Driver Development Guide
The Directory class of Makefiles directs the build process through
a set of subdirectories in a particular order. This order is usually
chosen to insure that build dependencies are properly processed.
Most BSPs only have one Directory class Makefile. The Makefile.in
in the BSP root directory (c/src/lib/libbsp/CPU/BSP) specifies
which directories are to be built for this BSP. For example, the
following Makefile fragment shows how a BSP would only build the
networking device driver if HAS_NETWORKING was defined:
NETWORKING_DRIVER_yes_V = network
NETWORKING_DRIVER = $(NETWORKING_DRIVER_$(HAS_NETWORKING)_V)
[...]
SUB_DIRS=include start340 startup clock console timer \
$(NETWORKING_DRIVER) wrapup
This fragment states that all the directories have to be processed,
except for the network directory which is included only if the
user configured networking.
BSP and Device Driver Development Guide
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