In the new HAL this is renamed to I2C_NOSTRETCH_DISABLE.

The custom IRQ handler only works for F4 MCUs, which have the SR1
register.

stdio.h was included in all HAL files only to provide
definition of NULL symbol

"stdio.h" includes "types.h" which contains some conflicting definitions
with "drivers/cc3000/inc/socket.h"

Use custom handlers providing minimal required functionality
because those provided by ST increase code size by almost 2 KiB.

HAL Driver before v1.4.2 had a bug which caused clearing all pending
flags in MSR, TSR, RF0R and RF1R instead of only the requested one.

This is why micropython got away without explicitly clearing flags
in IRQ handler.

Current version of HAL drivers checks if `hdma->State == HAL_DMA_STATE_READY`
before executing some functions.

Current version of HAL drivers optimize IRQ handler by using precalculated
DMA register address and stream bitshift instead of calculating it on every interrupt.

Since we skip call to `HAL_DMA_Init` on reused DMA, fields StreamBaseAddress and StreamIndex
of DMA handle are not initialized and thus leads to SegFault in `DMA_IRQHandler`.

HAL_DMA_Init is a big routine and we do not need to call it on each use of DMA
(ex.: series of I2C operations) and DMA_CalcBaseAndBitshift is really small and
releasing it increases code size by only 8 bytes.

This is required by HAL Driver for error handling since v1.5.0

CMSIS v2.5.0 removed all uint32_t casts and uses only Misra Cast (U)

changes include:
* use single GPIO.BSRR instead of BSRRH and BSRRL
* change HSE_STARTUP_TIMEOUT to 100 ms
* define LSE_STARTUP_TIMEOUT to 5 s

If a port defines MICROPY_READER_POSIX or MICROPY_READER_FATFS then
lexer.c now provides an implementation of mp_lexer_new_from_file using
the mp_reader_new_file function.

Implementations of persistent-code reader are provided for POSIX systems
and systems using FatFS.  Macros to use these are MICROPY_READER_POSIX and
MICROPY_READER_FATFS respectively.  If an alternative implementation is
needed then a port can define the function mp_reader_new_file.

Its addition was due to an early exploration on how to add CPython-like
stream interface. It's clear that it's not needed and just takes up
bytes in all ports.

This way the caller doesn't need to initialise a big GPIO_InitTypeDef
struct, and HAL_GPIO_Init is no longer called.

If an I2C send/recv fails then the peripheral is now checked to see if
it's in a "stuck" state waiting for the stop bit, and if so then it is
reset so that the next I2C transaction can proceed.

This patch also de-inits the I2C peripheral in the init() method, before
init'ing it again.

New keyword option in constructor and init() method is "dma=<bool>".
DMA is now disabled by default for I2C transfers because it currently does
not handle I2C bus errors very well (eg if slave device doesn't ACK or
NACK correctly during a transfer).

The DMA state is always HAL_DMA_STATE_RESET because of the memset clearing
all the data, so prior to this patch HAL_DMA_DeInit was never called.  Now
it is always called to make sure the DMA is properly reset.

Now, to use frozen bytecode all a port needs to do is define
FROZEN_MPY_DIR to the directory containing the .py files to freeze, and
define MICROPY_MODULE_FROZEN_MPY and MICROPY_QSTR_EXTRA_POOL.

Following best-practice use of the const feature, to make it compatible
with Python.

This allows it to be used only when the hardware supports VFP
instructions, preventing compile errors.

In order to have more fine-grained control over how builtin functions are
constructed, the MP_DECLARE_CONST_FUN_OBJ macros are made more specific,
with suffix of _0, _1, _2, _3, _VAR, _VAR_BETEEN or _KW.  These names now
match the MP_DEFINE_CONST_FUN_OBJ macros.

As defined in py/py.mk.