An network devices that supports netdev_driver_t::get(NETOPT_LINK, ...)
also has to emit NETDEV_EVENT_LINK_UP and NETDEV_EVENT_LINK_DOWN with
lwip for IPv6 duplicate address detection to work. The background is
that the STM32 Ethernet MAC requires a periodic timer to poll for the
state to emit these events. For this reason, `stm32_eth_link_up` was
introduced to allow applications to select if they need these events.
With this dependency in place, IPv6 addresses won't get stuck in a
tentative state any more.
Expose the auto-negotiation feature of the Ethernet device via the
pseudo-module stm32_eth_auto. With this enabled, the static speed configuration
set in the boards periph_conf.h will only be used if the PHY lacks
auto-negotiation capabilities - which is unlikely to ever happen.
The stm32_eth driver was build on top of the internal API periph_eth, which
was unused anywhere. (Additionally, with two obscure exceptions, no functions
where declared in headers, making them pretty hard to use anyway.)
The separation of the driver into two layers incurs overhead, but does not
result in cleaner structure or reuse of code. Thus, this artificial separation
was dropped.
The STM32 line of microcontrollers comes with a bootloader in the ROM.
It provides the option to flash the device firmware in DFU mode (USB)
or via UART or SPI.
To enter the bootloader we have to jump to a specific address in memory,
but before reset the CPU to make sure the system is in a known state.
This enables us to use the usb_board_reset module on all STM32 platforms.
