Per CPython docs, "Registering a file descriptor that’s already registered
is not an error, and has the same effect as registering the descriptor
exactly once."
https://docs.python.org/3/library/select.html#select.poll.register
That's somewhat ambiguous, what's implemented here is that if fd si not
yet registered, it is registered. Otherwise, the effect is equivalent to
modify() method.
Usually this checking is done by VM on jump instructions, but for linear
sequences of instructions and builtin functions this won't happen. Particular
target of this change is long-running builtin functions like time.sleep().
This is a hack to free up TIM3 so that it can be used by the user.
Instead we use the PVD irq to call the USB VCP polling function, and
trigger it from SysTick (so SysTick itself does not do any processing).
The feature is enabled for pyboard lite only, since it lacks timers.
Consider the following scenario: SD card is being read by pyboard; USB
irq comes in for MSC read request; SD card needs to be read from within
USB irq while SD read is already ongoing. Such contention needs to be
avoided.
This patch provides a simple solution, to raise the irq priority above
that of the USB irq during SD DMA transfers. Pyboard and PC can now
read from the SD card at the same time (well, reads are interleaved).
As set by signal handler. This assumes that exception will be raised
somewhere else, which so far doesn't happen for single function call.
Still, it makes sense to handle that in some common place.
Dave Hylands
Paul Sokolovsky
Ryan Shaw
Damien George
fabien.lementec