Calling it from mp_init() is too late for some ports (like Unix), and leads
to incomplete stack frame being captured, with following GC issues. So, now
each port should call mp_stack_ctrl_init() on its own, ASAP after startup,
and taking special precautions so it really was called before stack variables
get allocated (because if such variable with a pointer is missed, it may lead
to over-collecting (typical symptom is segfaulting)).

Includes full version of pins.csv file with correct mapping of the Nucleo
STM32F401RE chip (LQFP64 package).

Functions added are:
- randint
- randrange
- choice
- random
- uniform

They are enabled with configuration variable
MICROPY_PY_URANDOM_EXTRA_FUNCS, which is disabled by default.  It is
enabled for unix coverage build and stmhal.

This allows FROZEN_DIR=some-directory to be specified on the make
command line, which will then add all of the files contained within
the indicated frozen directory as frozen files in the image.

There is no change in flash/ram usage if not using the feature.

This is especially useful on smaller MCUs (like the 401) which only
has 64K flash file system.

Implement enough of statvfs to determine the amount of free
space on a volume.

Seedable and reproducible pseudo-random number generator. Implemented
functions are getrandbits(n) (n <= 32) and seed().

The algorithm used is Yasmarang by Ilya Levin:
http://www.literatecode.com/yasmarang

The first argument to the type.make_new method is naturally a uPy type,
and all uses of this argument cast it directly to a pointer to a type
structure.  So it makes sense to just have it a pointer to a type from
the very beginning (and a const pointer at that).  This patch makes
such a change, and removes all unnecessary casting to/from mp_obj_t.

They are no longer needed because stm constants can now be 32 bits wide.

Adds 924 bytes of code, but means that no more hacks and work-arounds are
needed due to large constants becoming negative.

The USB REPL has been broken since commit 1be0fde4
This patch allows the STM32F429DISC board (which uses the USB_HS PHY)

Adds a lot of code, makes IRQs a bit less efficient, but is very useful
for debugging.  Usage: pyb.irq_stats() returns a memory view that can be
read and written, eg:

    list(pyb.irq_stats())
    pyb.irq_stats()[0]
    pyb.irq_stats()[0] = 0

The patch provides general IRQ_ENTER() and IRQ_EXIT() macros that can be
modified to provide further IRQ statistics if desired.

This uses the newly factored machine_mem functions.

Changes USB clock from 50MHz to 48MHz which improves USB communication.

To let unix port implement "machine" functionality on Python level, and
keep consistent naming in other ports (baremetal ports will use magic
module "symlinking" to still load it on "import machine").

Fixes #1701.

Similar to recently added feature in unix port: if event triggers for an
objects, its polling flags are automatically reset, so it won't be polled
until they are set again explicitly.

This includes SPI4, SPI5 and SPI6.

This makes it much easier to understand which arg is which, less error
prone, and simpler to add a new arg.

Previously, SPI was configured by a board defining MICROPY_HW_ENABLE_SPIx
to 0 or 1.  Now, the board should define MICROPY_HW_SPIx_SCK, MISO, MOSI
and NSS.  This makes it the same as how I2C is configured.

Signed-off-by: Sven Wegener <sven.wegener@stealer.net>

This way mp_float_t can be changed to, eg, double.

This is refactoring to enable support for the two USB PHYs available on
some STM32F4 processors to be used at the same time. The F405/7 & F429
have two USB PHYs, others such as the F411 only have one PHY.

This has been tested separately on a pyb10 (USB_FS PHY) and F429DISC
(USB_HS PHY) to be able to invoke a REPL/USB.  I have modified a PYBV10
to support two PHYs.

The long term objective is to support a 2nd USB PHY to be brought up as a
USB HOST, and possibly a single USB PHY to be OTG.

Currently nlr_jump_fail prints that there was an uncaught exception
but nothing about the exception.
This patch causes nlr_jump_failed to try to print the exception.
Given that printf was called on the line above, I think that
the call to mp_obj_print_exception has about as much likelyhood
of succeeding as the printf does.

When you use the USER button to perform a filesystem reset
at boot time then it wipes out the filesystem and creates
a new boot.py and main.py.  With this patch these files are
executed after formatting, ensuring that pyb and machine modules
get imported.

This is a hack to free up TIM3 so that it can be used by the user.
Instead we use the PVD irq to call the USB VCP polling function, and
trigger it from SysTick (so SysTick itself does not do any processing).

The feature is enabled for pyboard lite only, since it lacks timers.

Consider the following scenario: SD card is being read by pyboard; USB
irq comes in for MSC read request; SD card needs to be read from within
USB irq while SD read is already ongoing.  Such contention needs to be
avoided.

This patch provides a simple solution, to raise the irq priority above
that of the USB irq during SD DMA transfers.  Pyboard and PC can now
read from the SD card at the same time (well, reads are interleaved).

These can be used to disable only certain interrupts, ones at or above
the given priority value.

In non-blocking mode (timeout=0), uart.write() can now transmit all of its
data without raising an exception.  uart.read() also works correctly in
this mode.

As part of this patch, timout_char now has a minimum value which is long
enough to transfer 1 character.

Addresses issue #1533.

With these you can now do things like:

stm.mem32[0x20000000] = 0x80000000

and read 32-bit values. You can also read all the way to the end
of memory using either stm.mem32[0xfffffffc] or stm.mem32[-4].

IRQs shouldn't use mem32 at all since they'd fail if the top 2 bits
weren't equal, so IRQs should be using 16-bit I/O.

The STMCube examples define both USE_USB_HS and USE_USB_HS_IN_FS when they
use the HS in FS mode.

The STM32F401 doesn't have a USB_HS at all, so the USB_OTG_HS instance
doesn't even exist.