Because py/mpconfig.h has header include guards.

The patch solves the problem where multiple Timer objects (e.g. multiple
Timer(0) instances) could initialise multiple handles to the same internal
timer.  The list of timers is now maintained not for "active" timers (where
init is called), but for all timers created.  The timers are only removed
from the list of timers on soft-reset (machine_timer_deinit_all).

Fixes #4078.

To enable define MICROPY_HW_USB_CDC_NUM to 3.

The board config option MICROPY_HW_USB_ENABLE_CDC2 is now changed to
MICROPY_HW_USB_CDC_NUM, and the latter should be defined to the maximum
number of CDC interfaces to support (defaults to 1).

Otherwise flushing and disabling the D-cache will give a hard-fault when
SDRAM is used.

Fixes #4818.

EAGAIN should be for pure non-blocking mode and ETIMEDOUT for when there is
a finite (but non-zero) timeout enabled.

Set the active MPU region to the actual size of SDRAM configured and
invalidate the rest of the memory-mapped region, to prevent errors due to
CPU speculation.  Also update the attributes of the SDRAM region as per ST
recommendations, and change region numbers to avoid conflicts elsewhere in
the codebase (see eth usage).

Fixes issue #4795.

I2C can't be enabled in prj_base.conf because it's a board-specific
feature.  For example, if a board doesn't have I2C but CONFIG_I2C=y then
the build will fail (on Zephyr build system side).  The patch here gets the
qemu_cortex_m3 build working again.

So it fits better with existing narrative.

This enables going back to previous wrapped lines using backspace or left
arrow: instead of just sticking to the beginning of a line, the cursor will
move a line up.

As part of this, ctrl-C is now able to interrupt a running program.

Defining NRFX_STATIC_ASSERT macro to be empty, but available
to nrfx.

On MCUs that have an I2C TIMINGR register, this can now be explicitly set
via the "timingr" keyword argument to the I2C constructor, for both
machine.I2C and pyb.I2C.  This allows to configure precise timing values
when the defaults are inadequate.

Previously the hardware I2C timeout was hard coded to 50ms which isn't
guaranteed to be enough depending on the clock stretching specs of the I2C
device(s) in use.

This patch ensures the hardware I2C implementation honors the existing
timeout argument passed to the machine.I2C constructor.  The default
timeout for software and hardware I2C is now 50ms.

Fixes issue #4794.

For modules I initially created or made substantial contributions to.

Recent gcc versions (at least 9.1) give a warning about using "sp" in the
clobber list.  Such code is removed by this patch.  A dedicated function is
instead used to set SP and branch to the bootloader so the code has full
control over what happens.

Fixes issue #4785.

This also fixes deleting the PPP task, since eTaskGetState() never returns
eDeleted.

A limitation with this patch: once the PPP is deactivated (ppp.active(0))
it cannot be used again. A new PPP instance must be created instead.

Only the M4 and M7 MCUs have an FPU and FPU_IRQn, and FPU_IRQn is not
always the last entry/IRQ number.

The H7 HAL uses SPI IRQs when the SPI is running in DMA mode.

This is required for the H7 DMA to work.

This allows figuring out the number of bytes in the memoryview object as
len(memview) * memview.itemsize.

The feature is enabled via MICROPY_PY_BUILTINS_MEMORYVIEW_ITEMSIZE and is
disabled by default.