The stack required for the idle thread is highly dependent on the
target because it will call the sleep function which is target
specific.
While 256 bytes of stack is enough for most targets, others like the
NRF52840 might require more.
With this change, target maintainers can specify the idle thread stack
size in their mbed_rtx.h file.
uVisor doesn't set the PSP of the target thread. The RTOS sets the PSP
of the target thread from the target thread's TCB. However, when
interrupts of higher priority than PendSV happen between the call to
uVisor to switch boxes, and the RTOS setting PSP, the uVisor vIRQ
interrupt handler will attempt to use an invalid PSP (the PSP from
before the box and thread switch). This leads to a crash. Make box and
thread switching atomic by disabling interrupts immediately before the
box switching until immediately after the new PSP is set.
Vincent Coubard
Russ Butler
Jimmy Brisson
Jaeden Amero
Bartosz Szatkowski
Yuguo Zou
Bartek Szatkowski