Replaces "PYB: soft reboot" with "MPY: soft reboot", etc.
Having a consistent prefix across ports reduces the difference between
ports, which is a general goal. And this change won't break pyboard.py
because that tool only looks for "soft reboot".
Instead of checking each callback (currently storage and dma) explicitly
for each SysTick IRQ, use a simple circular function table indexed by the
lower bits of the millisecond tick counter. This allows callbacks to be
easily enabled/disabled at runtime, and scales well to a large number of
callbacks.
This is a good board to demonstrate the use of Mboot because it only has a
USB HS port exposed so the native ST DFU mode cannot be used. With Mboot
this port can be used.
If a custom bootloader is enabled (eg mboot) then machine.bootloader() will
now enter that loader. To get the original ST DFU loader pass any argument
to the function, like machine.bootloader(1).
With clock bypass enabled the attached SD card is clocked at the maximum
48MHz. But some SD cards are unreliable at these rates. Although it's
nice to have high speed transfers it's more important that the transfers
are reliable for all cards. So disable this clock bypass option.
This way the UART REPL does not need the MicroPython heap and exists
outside the MicroPython runtime, allowing characters to still be received
during a soft reset.
The new compile-time option is MICROPY_HW_USB_MAX_POWER_MA. Set this in
the board configuration file to the maximum current in mA that the board
will draw over USB. The default is 500mA.
The new compile-time option is MICROPY_HW_USB_SELF_POWERED. Set this
option to 1 in the board configuration file to indicate that the USB device
is self powered. This option is disabled by default (previous behaviour).
It can be that LSEON and LSERDY are set yet the RTC is not enabled (this
can happen for example when coming out of the ST DFU mode on an F405 with
the RTC not previously initialised). In such a case the RTC is never
started because the code thinks it's already running. This patch fixes
this case by always checking if RTCEN is set when booting up (and also
testing for a valid RTCSEL value in the case of using an LSE).
Without the static qualifier these objects will be kept by the linker even
if they are unused. So this patch saves some RAM when these features are
unused by a board.
