When FreeRTOS semaphores, as required by ESP-IDF, are used together with `gnrc_netif`, RIOT may crash if `STATUS_RECEIVE_BLOCKED` is used as a blocking mechanism in the FreeRTOS adaptation layer. The reason for this is that `gnrc_netif` uses thread flags since PR #16748. If the `gnrc_netif` thread is blocked because of a FreeRTOS semaphore, and is thus in `STATUS_RECEIVE_BLOCKED` state, the `_msg_send` function will cause a crash because it then assumes that `target->wait_data` contains a pointer to a message of type `msg_t`, but by using thread flags it contains the flag mask. This situation can happen if the ESP hardware is used while another thread is sending something timer controlled to the `gnrc_netif` thread.
To solve this problem `STATUS_MUTEX_LOCKED` is used instead of `STATUS_RECEIVE_BLOCKED` and `STATUS_SEND_BLOCKED`
The definition of gettimeofday in pkg/ccn-lite leads to multiple definitions on platforms where gettimeofday is compiled in in newlib. Therefore, the gettimeofday function in pkg/ccn-lite is declared as weak symbol.
To reduce the required RAM in default configuration, the BLE interface is used as netdev_default instead of ESP-NOW. Further network interfaces can be enabled with the modules `esp_now`, `esp_wifi` or `esp_eth`.
When using Bluetooth LE, the former UART interrupt number 5 is occupied by the ESP32 Bluetooth Controller. Therefore, another interrupt number has to be used for UART.
The package uses the nRFx SDK package `nrfx`. In addition, the `mynewt-nimble` repository contains some files (`porting/nimble/src/hal_timer.c` and `porting/npl/riot/src/nrf5x_isr.c`) that are compilable only for nRF MCUs. To allow the compilation for other platforms, the use of the `nrfx` package and the compilation of these files are now dependent on the use of any nRF5x MCU.
If the package is used for a controller that supports the HCI UART H4 transport layer protocol, the functions implemented in `nimble/transport/common/hci_h4` are very useful to deal with H4 formatted packages. If required, they can be enabled by module `nimble_transport_hci_h4`.
