This constant is no longer part of hardware API (replaced with just None),
and is a default, so not needed in calls.

Also raise an exception for machine.freq and machine.deepsleep on this
MCU, since they are not yet implemented.

The main thing is to change the DMA code in a way that the structure
DMA_Stream_TypeDef (which is similar to DMA_Channel_TypeDef on stm32l4)
is no longer used outside of dma.c, as this structure only exists for the
F4 series.  Therefore I introduced a new structure (dma_descr_t) which
handles all DMA specific stuff for configuration.  Further the periphery
(spi, i2c, sdcard, dac) does not need to know the internals of the dma.

At http://micropython.org/webrepl .

.time() returns seconds since MicroPython epoch (2000-01-01 00:00UTC),
.settime() sends current system time, assuming UTC timezone.

Fixes issue #2023.

Querying/setting MAC address is pretty adhoc operation to belong to
.config() instead of taking a whole method on its own.

Instead of extracting 4th element, extact last. Much easier to remember!

Instead of extracting 4th element, extact last. Much easier to remember!

Useful for testing fragmentation issues in OS heap. E.g. freemem() may
report large amount, but is it possible to actually allocate block of
a given size? Issue malloc() (followed by free()) to find out.

Return number of free inernal WiFi buffers.

Returning free number of various WiFi driver packet buffers.