The vstr.had_error flag was a relic from the very early days which assumed
that the malloc functions (eg m_new, m_renew) returned NULL if they failed
to allocate.  But that's no longer the case: these functions will raise an
exception if they fail.

Since it was impossible for had_error to be set, this patch introduces no
change in behaviour.

An alternative option would be to change the malloc calls to the _maybe
variants, which return NULL instead of raising, but then a lot of code
will need to explicitly check if the vstr had an error and raise if it
did.

The code-size savings for this patch are, in bytes: bare-arm:188,
minimal:456, unix(NDEBUG,x86-64):368, stmhal:228, esp8266:360.

With the previous patch combining 3 emit functions into 1, it now makes
sense to also combine the corresponding VM opcodes, which is what this
patch does.  This eliminates 2 opcodes which simplifies the VM and reduces
code size, in bytes: bare-arm:44, minimal:64, unix(NDEBUG,x86-64):272,
stmhal:92, esp8266:200.  Profiling (with a simple script that creates many
list/dict/set comprehensions) shows no measurable change in performance.

The 3 kinds of comprehensions are similar enough that merging their emit
functions reduces code size.  Decreases in code size in bytes are:
bare-arm:24, minimal:96, unix(NDEBUG,x86-64):328, stmhal:80, esp8266:76.

Instead of busy-looping waiting for UART input. Not enabled by default,
needs more testing.

Based on https://github.com/micropython/micropython/pull/2210 .

A port now just needs to define FROZEN_DIR var and add $(BUILD)/frozen.c
to SRC_C to support frozen modules.

With FROZEN_MPY_DIR.

Takes element primitive type encoded as a char per standard JNI encoding,
and array size. TODO: Support object arrays.

bool(None) has a fast path in mp_obj_is_true so doesn't need to be
handled in none_unary_op.  The only caveat is that subclassing may
bypass the mp_obj_is_true function, but actually you aren't allowed to
subclass classes that have singleton instances like NoneType (see
https://mail.python.org/pipermail/python-dev/2002-March/020822.html for
reference on this point).

The algorithm here should mirror that in the machine.freq() function.

This is actually long overdue: the README in the windows directory has been
updated once to indicate mingw32 is abandoned and not ok to use with uPy,
but we forgot travis builds were still using it.
As a bonus the travis build will succeed again since moduerrno.c now compiles.
(see https://github.com/micropython/micropython/pull/2399)

This also fixes the test failure for vfs_fat_ramdisk.py

py/makeqstrdefs.py declares that it works with python 2.6 however the
syntax used to initialise of a set with values was only added in python
2.7. This leads to build failures when the host system doesn't have
python 2.7 or newer.

Instead of using the new syntax pass a list of initial values through
set() to achieve the same result. This should work for python versions
from at least 2.6 onwards.

Helped-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Chris Packham <judge.packham@gmail.com>

If a user tries to call `swint()` while interrupt is disabled the flag in
SWIER is set but the interrupt is not triggered and therefore the SWIER bit
is not cleared.  When the interrupt is again enabled the next call to
`swint()` won't trigger the IRQ because a 0 to 1 transition will not occur.

different HAL versions implement GPIO differently (BSRR vs BSRRH+BSRRL),
this way both drivers are portable between different HAL's

The LCD interface library fails to deassert the chip select of the LCD
after an SPI transmission.  Consequently using the SPI with other
peripherals disturbs the state of the LCD.  This patch changes
lcd.lcd_out() to deassert CS after each transmission to the LCD.

Tested on a STM32F7DISCO at 216MHz.  All tests generating code (inlineasm,
native, viper) now pass, except pybnative/while.py, but that's because
there is no LED(2).

It has reliability issues (cause unknown at this time).

machine.POWER_ON is renamed to machine.PWRON_RESET to match other
reset-cause constants that all end in _RESET.  The cc3200 port keeps a
legacy definition of POWER_ON for backwards compatibility.

- Refers to the technique of instantiating an object for use in an ISR by
  specifying it as a default argument.

- Footnote detailing the fact that interrupt handlers continue to be
  executed at the REPL.

When dealing with a board which controls chip reset with UART's DTR/RTS,
we never see REASON_DEFAULT_RST (0), only REASON_EXT_SYS_RST (6). However,
trying a "raw" module with with just TXD/RXD UART connection, on power up
it has REASON_DEFAULT_RST as a reset reason.

According to the Arduino ESP8266 implementation the first argument to the
wifi scan callback is actually a bss_info pointer.  This patch fixes the
iteration over this data so the first 2 entries are no longer skipped.

Fixes issue #2372.

Interrupts during neopixel_write causes timing problems and therefore
wrong light patterns.  Switching off IRQs should help to keep the strict
timing schedule.

It's built first in case any ports need to use it.

They require mp_hal_stdout_tx_strn_cooked, which requires extra work to
add to mpy-cross.