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https://gitlab.rtems.org/rtems/rtos/rtems.git
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Sebastian Huber
e74cea4172
The _ARMV7M_Pendable_service_call() and _ARMV7M_Supervisor_call() work
as a team. The --ef and ++ef is there to preserve the original exception
frame across the jump to and from _ARMV7M_Thread_dispatch().
void _ARMV7M_Pendable_service_call( void )
{
Per_CPU_Control *cpu_self = _Per_CPU_Get();
/*
* We must check here if a thread dispatch is allowed. Right after a
* "msr basepri_max, %[basepri]" instruction an interrupt service may
still
* take place. However, pendable service calls that are activated during
* this interrupt service may be delayed until interrupts are enable
again.
*/
if (
( cpu_self->isr_nest_level |
cpu_self->thread_dispatch_disable_level ) == 0
) {
ARMV7M_Exception_frame *ef;
cpu_self->isr_nest_level = 1;
_ARMV7M_SCB->icsr = ARMV7M_SCB_ICSR_PENDSVCLR;
_ARMV7M_Trigger_lazy_floating_point_context_save();
At this point, the floating point context should be saved on the
exception frame. The FPCCR.LSPACT bit should be 0, to indicate that lazy
state preservation is no longer active.
ef = (ARMV7M_Exception_frame *) _ARMV7M_Get_PSP();
--ef;
_ARMV7M_Set_PSP( (uint32_t) ef );
This new exception frame is just there to jump to
_ARMV7M_Thread_dispatch(). Here was the problem, that FPCCR.LSPACT was
not set to 1. This resulted in a floating-point context from
uninitialized memory which could corrupt the floating-point state. See
also:
https://developer.arm.com/documentation/ddi0403/d/System-Level-Architecture/System-Level-Programmers--Model/ARMv7-M-exception-model/Exception-return-behavior?lang=en
/*
* According to "ARMv7-M Architecture Reference Manual" section B1.5.6
* "Exception entry behavior" the return address is half-word aligned.
*/
ef->register_pc = (void *)
((uintptr_t) _ARMV7M_Thread_dispatch & ~((uintptr_t) 1));
ef->register_xpsr = 0x01000000U;
}
}
Close #4923.
Real-Time Executive for Multiprocessing Systems
RTEMS is a real-time executive (kernel) which provides a high performance environment for embedded applications with the following features:
- Standards based user interfaces.
- Multitasking capabilities.
- Homogeneous and heterogeneous multiprocessor systems.
- Event-driven, priority-based, preemptive scheduling.
- Optional rate monotonic scheduling.
- Intertask communication and synchronisation.
- Priority inheritance.
- Responsive interrupt management.
- Dynamic memory allocation.
- High level of user configurability.
- Open source with a friendly user license.
Project git repositories are located at:
Online documentation is available at:
RTEMS Doxygen for CPUKit:
RTEMS POSIX 1003.1 Compliance Guide:
RTEMS Mailing Lists for general purpose use the users list and for developers use the devel list.
The version number for this software is indicated in the VERSION file.