Since the very beginning, the stm32 port (first called stm, then stmhal now
stm32) has had a special keyboard interrupt feature which works by using
PendSV to break out of any running code. This preemptive ctrl-C was added
long ago in commit 01156d510c728408be4fd3100bcee18e8985ac00.
The stm32 port still uses that code, and current does this:
- If ctrl-C is received on UART or USB then `mp_sched_keyboard_interrupt()`
is called (like all other ports) to set a flag for the VM to see, and
then the VM (or any loop calling `mp_handle_pending(true)`) will
eventually handle the `KeyboardInterrupt` exception, raising it via NLR.
- If another ctrl-C is received while the existing scheduled keyboard
interrupt is still pending (ie the VM has not yet processed it) then a
special hard NLR jump will activate, that preempts the calling code.
Within the PendSV interrupt the stack is adjusted and an NLR jump is made
to the most recent `nlr_push()` location. This is like a normal NLR
except it is called from an interrupt context and completely annihilates
the code that was interrupted by the IRQ.
The reason for the preemptive interrupt was to handle ctrl-C before the VM
was able to handle it. Eventually a mechanism (that's in use today by all
ports) was added to the VM and runtime to be able to check for pending
interrupts. Then the stm32 port was updated to use this mechanism, with a
fallback to the old preemptive way if a second ctrl-C was received (without
the first one being processed).
This preemptive NLR jump is problematic because it can interrupt
long-running instructions (eg store multiple, usually used at the end of a
function to restore registers and return). If such an instruction is
interrupted the CPU remembers that with some flags, and can resume the
long-running instruction when the interrupt finishes. But the preemptive
NLR does a long jump to different code at thread level and so the
long-running interrupt is never resumed. This leads to a CPU fault.
This fault has been previously reported in issues #3807 and #3842 (see also
issue #294). It's now possible to easily reproduce this problem, since
commit 69c25ea8653566ec97690b5121bd10b753c89426. Running the test suite
over and over again on any stm32 board will eventually crash the board (it
can happen on a PYBv1.x, but it happens more regularly on PYBD-SF2/6).
The point is, a skipped test now soft resets the board and so the board
must run `boot.py` again. The test runner may then interrupt the execution
of `boot.py` with the double-ctrl-C that it sends (in `tools/pyboard.py`,
`enter_raw_repl()`) in order to get the board into a known good state for
the next test. If the timing is right, this can trigger the preemptive
PendSV in an unfortunate location and hard fault the board.
The fix in this commit is to just remove the preemptive NLR jump feature.
No other port has this feature and it's not needed, ctrl-C works very well
on those ports. Preemptive NLR jump is a very dangerous thing (eg it may
interrupt and break out of an external SPI flash operation when reading
code from a filesystem) and is obviously buggy.
With this commit, stm32 borads no longer hard fault when running the test
suite (but it does leave an issue, the tests can still interrupt `boot.py`
with a single ctrl-C; that will be fixed separately).
An alternative to this commit would be to clear the CPU state for the
long-running instruction as suggested in issue #3842. But it's much
simpler to just remove this code, which is now unnecessary and can have
other problems as per issue #294.
Signed-off-by: Damien George <damien@micropython.org>
This introduces a new macro to get the main thread and uses it to ensure
that asynchronous exceptions such as KeyboardInterrupt (CTRL+C) are only
scheduled on the main thread. This is more deterministic than being
scheduled on a random thread and is more in line with CPython that only
allow signal handlers to run on the main thread.
Fixes issue #7026.
Signed-off-by: David Lechner <david@pybricks.com>
This moves mp_pending_exception from mp_state_vm_t to mp_state_thread_t.
This allows exceptions to be scheduled on a specific thread.
Signed-off-by: David Lechner <david@pybricks.com>
For a given IRQn (eg UART) there's no need to carry around both a PRI and
SUBPRI value (eg IRQ_PRI_UART, IRQ_SUBPRI_UART). Instead, the IRQ_PRI_UART
value has been changed in this patch to be the encoded hardware value,
using NVIC_EncodePriority. This way the NVIC_SetPriority function can be
used directly, instead of going through HAL_NVIC_SetPriority which must do
extra processing to encode the PRI+SUBPRI.
For a priority grouping of 4 (4 bits for preempt priority, 0 bits for the
sub-priority), which is used in the stm32 port, the IRQ_PRI_xxx constants
remain unchanged in their value.
This patch also "fixes" the use of raise_irq_pri() which should be passed
the encoded value (but as mentioned above the unencoded value is the same
as the encoded value for priority grouping 4, so there was no bug from this
error).
Header files that are considered internal to the py core and should not
normally be included directly are:
py/nlr.h - internal nlr configuration and declarations
py/bc0.h - contains bytecode macro definitions
py/runtime0.h - contains basic runtime enums
Instead, the top-level header files to include are one of:
py/obj.h - includes runtime0.h and defines everything to use the
mp_obj_t type
py/runtime.h - includes mpstate.h and hence nlr.h, obj.h, runtime0.h,
and defines everything to use the general runtime support functions
Additional, specific headers (eg py/objlist.h) can be included if needed.
This is to keep the top-level directory clean, to make it clear what is
core and what is a port, and to allow the repository to grow with new ports
in a sustainable way.
