stm32/boards: Enable LTO by default on boards with smaller flash size.

Signed-off-by: Angus Gratton <gus@projectgus.com>
micropython · Jun 28, 2022 · dd77dbd · dd77dbd
1 parent 5568c32
commit dd77dbd
Show file tree

Hide file tree

Showing 6 changed files with 32 additions and 0 deletions.
diff --git a/ports/stm32/README.md b/ports/stm32/README.md
@@ -68,6 +68,23 @@ can be built via:
 
 For more information about mboot see mboot/README.md.
 
+### Link Time Optimization
+
+Link Time Optimization (LTO) reduces the firmware binary size when enabled
+(typically 2-3% smaller). However it may make build time longer, particularly on
+older GCC versions.
+
+Currently LTO is enabled by default for some smaller STM32 boards with less
+flash, but disabled on other boards.
+
+To enable LTO, pass `LTO=1` on the command line:
+
+    $ make BOARD=boardname LTO=1
+
+To disable LTO, pass `LTO=0` in the same way.
+
+Note that `make clean BOARD=boardname` will be needed before changing the `LTO`
+setting of a firmware that is already built.
 
 ### Flashing the Firmware using DFU mode
 

diff --git a/ports/stm32/boards/B_L072Z_LRWAN1/mpconfigboard.mk b/ports/stm32/boards/B_L072Z_LRWAN1/mpconfigboard.mk
@@ -9,3 +9,6 @@ MICROPY_VFS_FAT = 0
 
 # Don't include default frozen modules because MCU is tight on flash space
 FROZEN_MANIFEST ?=
+
+# LTO reduces final binary size, may be slower to build depending on gcc version and hardware
+LTO ?= 1
diff --git a/ports/stm32/boards/NUCLEO_F091RC/mpconfigboard.mk b/ports/stm32/boards/NUCLEO_F091RC/mpconfigboard.mk
@@ -9,3 +9,6 @@ MICROPY_VFS_LFS1 ?= 1
 
 # Don't include default frozen modules because MCU is tight on flash space
 FROZEN_MANIFEST ?=
+
+# LTO reduces final binary size, may be slower to build depending on gcc version and hardware
+LTO ?= 1
diff --git a/ports/stm32/boards/NUCLEO_G0B1RE/mpconfigboard.mk b/ports/stm32/boards/NUCLEO_G0B1RE/mpconfigboard.mk
@@ -2,3 +2,6 @@ MCU_SERIES = g0
 CMSIS_MCU = STM32G0B1xx
 AF_FILE = boards/stm32g0b1_af.csv
 LD_FILES = boards/stm32g0b1xe.ld boards/common_basic.ld
+
+# LTO reduces final binary size, may be slower to build depending on gcc version and hardware
+LTO ?= 1
diff --git a/ports/stm32/boards/NUCLEO_L073RZ/mpconfigboard.mk b/ports/stm32/boards/NUCLEO_L073RZ/mpconfigboard.mk
@@ -8,3 +8,6 @@ MICROPY_VFS_FAT = 0
 
 # Don't include default frozen modules because MCU is tight on flash space
 FROZEN_MANIFEST ?=
+
+# LTO reduces final binary size, may be slower to build depending on gcc version and hardware
+LTO ?= 1
diff --git a/ports/stm32/boards/NUCLEO_L432KC/mpconfigboard.mk b/ports/stm32/boards/NUCLEO_L432KC/mpconfigboard.mk
@@ -10,3 +10,6 @@ MICROPY_VFS_LFS1 ?= 1
 
 # Don't include default frozen modules because MCU is tight on flash space
 FROZEN_MANIFEST ?=
+
+# LTO reduces final binary size, may be slower to build depending on gcc version and hardware
+LTO ?= 1