This function is not used by the core but having it as part of the build
allows it to be used by user C modules, or board extensions.  The linker
won't include it in the final firmware if it remains unused.

This gets tests/extmod/uselect_poll_basic.py working on the esp32.

This replaces 0 and 1 with STDIN_FILENO and STDOUT_FILENO to make the
intention of the code clearer.

This removes the port-specific definition of MP_PLAT_PRINT_STRN on the
windows port, so that the default mp_hal_stdout_tx_strn_cooked() is always
used.  This fixes releasing the GIL during the call to write() (this was
missed in bc3499f0).

Also, mp_hal_dupterm_tx_strn() was defined but never used anywhere so it is
safe to delete it.

This removes the port-specific definition of MP_PLAT_PRINT_STRN on the unix
port.  Since fee7e561 this is no longer a
single function call so we are not really optimising anything over using
the default definition of MP_PLAT_PRINT_STRN which calls
mp_hal_stdout_tx_strn_cooked().

Fixes issue #5780.

Using new options enabled in the uncrustify configuration.

Fix missing mkdir and gettimeofday declarations, then silence msvc-specific
compiler warning C4996: 'The POSIX name for this item is deprecated'.

Zephyr v2.2 reworked its gpio api to support linux device tree bindings and
pin logical levels.  This commit updates the zephyr port's machine.Pin
class to replace the deprecated gpio api calls with the new supported gpio
api.  This resolves several build warnings.

Tested on frdm_k64f and mimxrt1050_evk boards.

The "led" argument is always a pointer to the GPIO port, or'd with the pin
that the LED is on, so testing that it is "1" is unnecessary.  The type of
"led" is also changed to uint32_t so it can properly hold a 32-bit pointer.

Updating the LED0 state from systick handler ensures LED0 is always
consistent with its flash rate regardless of other processing going on in
either interrupts or main.  This improves the visible stability of the
bootloader, rather than LED0 flashing somewhat randomly at times.

This commit also changes the LED0 flash rate depending on the current state
of DFU, giving slightly more visual feedback on what the device is doing.

And provide a DFU error message for invalid erases and writes.

Allows for custom functions/logic to display mboot state.

Also fix Espressif links to the specific version they apply to.

Fixes issue #5764.

The implementation in extmod/vfs_posix_file.c is now equivalent to that in
ports/unix/file.c, so remove the latter and use the former instead.

Fixes issue #5753.

Adds support in the zephyr port to execute main.py if the file system is
enabled and the file exists. Existing support for executing a main.py
frozen module is preserved, since pyexec_file_if_exists() works just
like pyexec_frozen_module() if there's no vfs.

Enables the zephyr usb device stack and mass storage class on the
mimxrt1050_evk board. The mass storage class is backed by the sdhc disk
access driver, so it's now possible to browse and modify the contents of
the SD card from a USB host (your PC). This is in preparation to support
writing a main.py script to the SD card, and then executing it after the
next reset.

Adds support in the zephyr port to mount a file system if a block device
(sdhc disk access or flash area) is available. The mount point is either
"/sd" or "/flash" depending on the type of block device.

Tested with an sdhc disk access block device and fatfs on the
mimxrt1050_evk board.

Tested with a flash area block device and littlefs on the reel_board.

This commit adds micropython.heap_locked() which returns the current
lock-depth of the heap, and can be used by Python code to check if the heap
is locked or not.  This new function is configured via
MICROPY_PY_MICROPYTHON_HEAP_LOCKED and is disabled by default.

This commit also changes the return value of micropython.heap_unlock() so
it returns the current lock-depth as well.

This is an extremely minimal port to the NXP i.MX RT, in the style of the
SAMD port  It's largely based on the TinyUSB mimxrt implementation, using
the NXP SDK.  It currently supports the Teensy 4.0 board with a REPL over
the USB-VCP interface.

This commit also adds the NXP SDK submodule (also from TinyUSB) to
lib/nxp_driver.

Note: if you already have the tinyusb submodule initialized recursively you
will need to run the following as the tinyusb sub-submodules have been
rearranged (upstream):

    git submodule deinit lib/tinyusb
    rm -rf .git/modules/lib/tinyusb
    git submodule update --init lib/tinyusb

This fixes a crash, caused by NimBLE continuing to call the Python BLE
interrupt handler after soft reboot.

Otherwise ets_loop_iter may be reentered.  Related to issue #5714.

Now all HCI specific code (eg UART vs WB55 internal messaging) is confined
to modbluetooth_hci.c.

Work done in collaboration with Jim Mussared aka @jimmo.

Work done in collaboration with Jim Mussared aka @jimmo.

Work done in collaboration with Jim Mussared aka @jimmo.

This makes a cleaner separation between the: driver, HCI UART and BT stack.
Also updated the naming to be more consistent (mp_bluetooth_hci_*).

Work done in collaboration with Jim Mussared aka @jimmo.

Move extmod/modbluetooth_nimble.* to extmod/nimble.  And move common
Makefile lines to extmod/nimble/nimble.mk (which was previously only used
by stm32).  This allows (upcoming) btstack to follow a similar structure.

Work done in collaboration with Jim Mussared aka @jimmo.

The bluetooth stack has its own dedicated polling function, see
mod_bluetooth_nimble_poll_wrapper().

sys.stdout.flush() is needed on CPython to flush the output, and the change
in this commit makes such an expression also work on MicroPython (although
MicroPython doesn't actual need to do any flushing).