[Core] Allow usage of AVRs minimal printf library (#16266)

Co-authored-by: Sergey Vlasov <sigprof@gmail.com>

1 files changed, 13 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.