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lancaster-university / microbit-v2-samples

CODAL build tools and sample programs for the micro:bit v2.x
MIT License
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Remove unnecessary use of global images in samples to save memory. #57

Closed carlosperate closed 1 year ago

carlosperate commented 1 year ago

Working on a side project I was looking at the memory map file for the default build and noticed a couple of functions/globals from unused samples that are somehow left inside the build, mostly a few global MicroBitImage and, I'm not sure how, but also a couple of uncalled functions: version_test and display_wink.

Some exerpts from the memory map file:

 .text.startup._GLOBAL__sub_I__Z12version_testv
                0x0000000000002c14       0x64 CMakeFiles/MICROBIT.dir/source/samples/PowerManagementTest.cpp.obj

 .rodata._Z12display_winkv.str1.4
                0x0000000000014624      0x105 CMakeFiles/MICROBIT.dir/source/samples/DisplayTest.cpp.obj
 .rodata._GLOBAL__sub_I_happy.str1.4
                0x000000000001472c       0x79 CMakeFiles/MICROBIT.dir/source/samples/DisplayTest.cpp.obj
 .rodata._GLOBAL__sub_I__Z12version_testv.str1.4
                0x000000000001523c      0x171 CMakeFiles/MICROBIT.dir/source/samples/PowerManagementTest.cpp.obj

 .bss.happy     0x0000000020001634        0x4 CMakeFiles/MICROBIT.dir/source/samples/DisplayTest.cpp.obj
                0x0000000020001634                happy
 .bss.sad       0x0000000020001638        0x4 CMakeFiles/MICROBIT.dir/source/samples/DisplayTest.cpp.obj
                0x0000000020001638                sad
 .bss._ZL2dc    0x00000000200016b0        0x4 CMakeFiles/MICROBIT.dir/source/samples/PowerManagementTest.cpp.obj
 .bss._ZL3usb   0x00000000200016b4        0x4 CMakeFiles/MICROBIT.dir/source/samples/PowerManagementTest.cpp.obj
 .bss._ZL7battery
                0x00000000200016b8        0x4 CMakeFiles/MICROBIT.dir/source/samples/PowerManagementTest.cpp.obj

 .ARM.attributes
                0x00000000000000d0       0x32 CMakeFiles/MICROBIT.dir/source/samples/DisplayTest.cpp.obj
 .ARM.attributes
                0x0000000000000166       0x32 CMakeFiles/MICROBIT.dir/source/samples/PowerManagementTest.cpp.obj

The minor modifications from this PR removes this unused data/code from the build, which saves 20 bytes of RAM and close to 1KB of flash:

# Before
$ arm-none-eabi-size build/MICROBIT
   text    data     bss     dec     hex filename
 216008       8    7164  223180   367cc build/MICROBIT

# After
$ arm-none-eabi-size build/MICROBIT
   text    data     bss     dec     hex filename
 215092       8    7144  222244   36424 build/MICROBIT