Using f_printf with FATFS

[diocorreia]

I'm having problems using f_printf function with nRF52 SDK v16

undefined reference to `f_printf'

Makefile is the same of FATFS example and already includes:

$(SDK_ROOT)/external/fatfs/port/diskio_blkdev.c \
$(SDK_ROOT)/external/fatfs/src/ff.c \

[diocorreia]

I used f_write with sprintf instead.