Note Mbedtls uses a function time which is, according to Cube MX default configuration, not defined from the platform but must come from the system environment.
From my understanding, the time body is missing in the generated project.
Regarding STM32 Cube for F7 (https://www.st.com/en/embedded-software/stm32cubef7.html, e-g en.STM32Cube_FW_F7_V1.15.0), you can find in the mbed TLS examples (e-g STM32756G_EVAL project) a time body in this file : retarget.c
=> The Link passed if you add this file in the Project Src folder and in the KEIL project (for compilation).
To summarise, interesting files are from :
- mbedtls, platform_time.h where time source is defined (based on MBEDTLS_PLATFORM_TIME_MACRO).
- Keil SW, retarget.c where time body is given for uVision/ARM development tool.