The UART interface and its configuration as used by the STDIO is defined in RIOT using `STDIO_UART_DEV` and the UART configuration in `periph_conf.h`.
However, the bootloader compiled directly in ESP-IDF uses its own definitions `CONFIG_ESP_CONSOLE_UART_*` for the UART configuration. To be able to use a consistent UART configuration in RIOT and the bootloader, e.g. to see the output of the 2nd stage bootloader, these `CONFIG_ESP_CONSOLE_UART_*` can be defined via a set of KConfig variables `CONSOLE_CONFIG_UART_*`. Here the variable `CONSOLE_CONFIG_UART_NUM` is then also used as `STDIO_UART_DEV` and the variables `CONSOLE_CONFIG_UART_RX` and `CONSOLE_CONFIG_UART_TX` of the configuration in `periph_conf.h` should be used accordingly.
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