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| -rw-r--r-- | docs/squeezing_avr.md | 13 | ||||
| -rw-r--r-- | platforms/avr/platform.mk | 9 |
2 files changed, 22 insertions, 0 deletions
diff --git a/docs/squeezing_avr.md b/docs/squeezing_avr.md index 62f0a5d290..f7e21d932b 100644 --- a/docs/squeezing_avr.md +++ b/docs/squeezing_avr.md @@ -30,6 +30,19 @@ MAGIC_ENABLE = no These features are enabled by default, but may not be needed. Double check to make sure, though. Largest in size is "magic" -- the QMK magic keycodes -- which control things like NKRO toggling, GUI and ALT/CTRL swapping, etc. Disabling it will disable those functions. +If you use `sprintf` or `snprintf` functions you can save around ~400 Bytes by enabling this option. +```make +AVR_USE_MINIMAL_PRINTF = yes +``` + +This will include smaller implementations from AVRs libc into your Firmware. They are [not fully featured](https://www.nongnu.org/avr-libc/user-manual/group__avr__stdio.html#gaa3b98c0d17b35642c0f3e4649092b9f1), for instance zero padding and field width specifiers are not supported. So if you use `sprintf` or `snprintf` like this: +```c +sprintf(wpm_str, "%03d", get_current_wpm()); +snprintf(keylog_str, sizeof(keylog_str), "%dx%d, k%2d : %c"); +``` + +you will still need the standard implementation. + ## `config.h` Settings If you've done all of that, and you don't want to disable features like RGB, Audio, OLEDs, etc, there are some additional options that you can add to your config.h that can help. diff --git a/platforms/avr/platform.mk b/platforms/avr/platform.mk index 9f304d2e20..0374e2e058 100644 --- a/platforms/avr/platform.mk +++ b/platforms/avr/platform.mk @@ -37,6 +37,15 @@ CXXFLAGS += -fno-exceptions -std=c++11 LDFLAGS += -Wl,--gc-sections +# Use AVR's libc minimal printf implementation which has less features +# and thus can shave ~400 bytes. Usually we use the xprintf +# implementation but keyboards that use s(n)printf automatically +# pull in the AVR libc implementation, which is ~900 bytes heavy. +AVR_USE_MINIMAL_PRINTF ?= no +ifeq ($(strip $(AVR_USE_MINIMAL_PRINTF)), yes) + LDFLAGS += -Wl,--whole-archive -lprintf_min -Wl,--no-whole-archive +endif + OPT_DEFS += -DF_CPU=$(F_CPU)UL MCUFLAGS = -mmcu=$(MCU) |