The bit access functions are not tied to Cortex-M CPUs, here they only
provide optimisations via bit-banding.
But the functions are generally useful - so move them to an arch independent
location.
This modifies the cortex-m thread specifics to allow running the PendSV
interrupt continuously at lower priority and removes the priority
modifications during the interrupt itself. Interrupts are disabled
during the scheduling itself, but enabled briefly after the sleep to
ensure that they are handled if activated during the scheduling or the
sleep.
Not all MCUs ≥ Cortex-M3 provide the Bit-Banding feature.
It is up to the manufacturer to implement it.
Instead, rely on the CPU_HAS_BITBAND being set in `periph_cpu.h`.
__set_PRIMASK(state) had been directly inlined to avoid a hardfault that
occured when branching after waking up from sleep with DBG_STANDBY,
DBG_STOP or DBG_SLEEP set in DBG_CR.
The hardfault occured when returning from the branch to irq_restore,
since the function is now inlined the branch does not happen either.
Refer to #14015 for more details.
irq_% are not inlined by the compiler which leads to it branching
to a function that actually implement a single machine instruction.
Inlining these functions makes the call more efficient as well as
saving some bytes in ROM.
This commit enables Cortex-M CPU interrupt sub-priorities
and allows the PendSV interrupt to have a priority different
from the default one. Together these two preprocessor
defines can be used to have PendSV always run as the last interrupt
before returning from the interrupt stack back to the user space.
Running PendSV as the last interrupt before returning to the
user space is recommended by ARM, as it increases efficiency.
Furthermore, that change enhances stability a lot with the
new nRF52 SoftDevice support, currently being worked in
PR #9473.
This commit merely enables sub-priorities and a separate
PendSV priority to be used without changing the default
RIOT behaviour.
- The __NOP() that was added in #8518 is now remooved.
- When DBG_STANDBY, DBG_STOP or DBG_SLEEP are set in DBG_CR a hardfault
occurs on wakeup from sleep. This was first diagnosed in #8518. When
enabled, a hardfault occured when returning from a branch to irq_restore()
we avoid the call by inlining the function call. See #11830 for more
details.
This new function allows to jump to another execution
environment (VTOR) located at a certain (aligned) address.
It's used to boot firmwares at another location than
`CPU_FLASH_BASE`.
The user needs to ensure that the CPU using this feature
is able to be initialised at least twice while jumping
to the RIOT `reset_handler_default` function, since it
initialises the CPU again (calls cpu_init()).
Co-authored-by: Kaspar Schleiser <kaspar@schleiser.de>
Refactor cortexm_init to allow bits and pieces of
it to be called separately, while retaining the
current API, too. Needed for non-standard
Cortex-M initialisation, such as with nRF52
SoftDevice.
Instead of using `weak` function definitions, this PR handles
default implementations using `PROVIDES_x` defines, allowing
for cpus/pm realted modules to use their own implementations.
