Add API to dynamically enable/disable input and output on FileHandles.
Aim is to allow power saving by indicating that we permanently or
temporarily do not require input, so that for example serial Rx
interrupts can be released, and deep sleep permitted.
SharedPtr::reset did not actually set the stored pointer value.
Correct this, with other minor tidies:
* Ensure counter is set to NULL if pointer is reset to NULL
* Be consistent about not clearing pointers in decrement_counter().
mbed_die was calling wait_ms in a critical section - this is deprecated
behaviour, and caused a fatal error in debug builds, potentially leading
to an infinite reboot loop if this was caused due to a reboot limit
halt.
Switch to using wait_us - this is safe in a critical section. This does
trigger a call to mbed_warning, due to the large parameter, but that is
harmless - it doesn't output anything to the console, and won't
overwrite the error context if it already contains something.
The pre-main check of error_reboot_count was applied repeatedly on
every boot, meaning that once the reboot limit was hit, every subsequent
reset would halt before main, until something managed to clear
or corrupt the error context.
Set the is_error_processed flag before halting, so that when an external
agent resets us while we're halted, we do not report the error and halt
again.
A couple of places in mbed_retarget.cpp were testing for either ARMC5 or
ARMC6 in a long-winded fashion. Testing for __ARMCC_VERSION being
defined is sufficient.
Similar to SingletonPtr, use atomic accesses when loading the guard word
outside the lock, and when storing, to ensure no races for threads that
don't take the lock.
Lack of atomics unlikely to be a problem in current builds, but code
could conceivably be subject to reordering if link-time optimisation was
enabled.
SingletonPtr's implementation wasn't totally safe - see "C++ and the
Perils of Double-Checked Locking"by Meyers and Alexandrescu. No problems
observed in practice, but it was potentially susceptible to compiler
optimisation (or maybe even SMP issues).
Now that we have atomic loads and stores, the function can be made safe,
avoiding any potential races for threads that don't take the lock:
ensure that the unlocked load is atomic, and that the pointer store is
atomic.
See https://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/
for more discussion.
As barriers were added in #9247, review comments pointed out that atomic
stores needed a second barrier, and they got one. But atomic_flag_clear
was missed.
Add atomic load and store functions, and add barriers to the existing atomic
functions.
File currently has no explicit barriers - we don't support SMP, so don't
need CPU barriers.
But we do need to worry about compiler barriers - particularly if link time
optimisation is activated so that the compiler can see inside these
functions. The assembler or intrinsics that access PRIMASK for
enter/exit critical act as barriers, but LDREX, STREX and simple
volatile pointer loads and stores do not.
Critical section count/state variables are synchronised by IRQ disabling and
critical section calls themselves, so do not need to be volatile.
This eliminates a couple of unnecessary reads of the counter variable.
The DEVICE_FOO macros are always defined (either 0 or 1).
This patch replaces any instances of a define check on a DEVICE_FOO
macro with value test instead.
Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
As part of work to improve the debugging of exceptions, have
Mbed OS make an effort to make exceptions more precise in debug builds
at the cost of performance.
Related pyOCD work:
https://github.com/mbedmicro/pyOCD/pull/430
Make the option positively named, and as it is a platform config
option make sure it only affects platform code.
HAL functions still remain available even if platform is told not
to use them.
MPU lock under- or overflow is not a likely random runtime failure - it
will be a mismatched lock/unlock programming error, so should be
detected during development. Make the checks asserts so they can be
left out from release builds. MBED_ASSERT is also a bit smaller than
MBED_ERROR in develop builds.
Kevin Bracey
Martin Kojtal
Cruz Monrreal
Senthil Ramakrishnan
paul-szczepanek-arm
Deepika
kegilbert
bcostm
Alastair D'Silva
Russ Butler
Filip Jagodzinski