Skip list is a "random" data structure that in high possibilities it
would get O(log(N)) time complexity in inserting while the old list get
O(N). Forthermore, when set RT_TIMER_SKIP_LIST_LEVEL to 1, it will just
the same as the old double linked list, both in time and space
complexity.
Benchmarks shows that when RT_TIMER_SKIP_LIST_LEVEL is 3, the average
time of random insertion of new timer is about 2 times faster than the
old timer when there are 100 timers and 3 times faster when there are
200 timers.
However, it restores the deprecated funcion rt_system_timer_init. BSPs
must invoke it upon system startup.
In thread context means: 1) the scheduler has been started; 2) not in
interrupt context. It is more stronger than RT_DEBUG_NOT_IN_INTERRUPT.
With this commit, you will catch the error on situations like taking
mutex before scheduling instead of crashing on NULL pointer reference.
vsnprintf is a common string function that could be used in many places.
Using both vsnprintf in libc and vsnprintf in the RTT could make a
bigger image. Moreover, if newlib is not enabled when compiling with
GCC, referencing vsnprintf will lead to link error:
.../arm-none-eabi/lib/armv7-ar/thumb/softfp/libc.a(lib_a-sbrkr.o):
In function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0xc): undefined reference to `_sbrk'
collect2: error: ld returned 1 exit status
Using rt_vsnprintf could avoid such problem.
Portal is a device that connect devices. Currently, you can only connect
pipes in portal. Pipes are unidirectional. But with portal, you can
construct a bidirectional device with two pipes.
This is a simple work around to the current device stack design. A
ref_count could let different modules to open/close the same device
independently without interfere others in some degree.
But there is still some data shared between the modules, like flag,
open_flag and user_data. Moreover, it won't yield an error if A open a
device, and B read from it before open it in B. Maybe alloc a new handle
in rt_device_open will be the ultimate solution. But that is much bigger
change and we may leave it to future development.
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