rt 0.19.1

A real-time operating system capable of full preemption
Documentation 
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#include <rt/abort.h>
#include <rt/context.h>
#include <rt/cycle.h>
#include <rt/idle.h>
#include <rt/interrupt.h>
#include <rt/mpu.h>
#include <rt/syscall.h>
#include <rt/task.h>
#include <rt/tls.h>
#include <rt/trap.h>

#include <rt/arch/fp.h>
#include <rt/arch/profile.h>

#include <stddef.h>
#include <stdint.h>

#if RT_ARM_PROFILE_AR
#include "ar/ar.c"
#elif RT_ARM_PROFILE_M
#include "m/m.c"
#endif

void *rt_context_init(uintptr_t fn, uintptr_t arg, void *stack,
                      size_t stack_size)
{
    void *const sp = (char *)stack + stack_size;
    struct context *ctx = sp;
    --ctx;
    profile_context_init(ctx);
#if RT_ARM_V8M
    /* V8M is the only variant with additional state based on the stack, so set
     * that here rather than pass the stack to profile_context_init. */
    ctx->psplim = (uint32_t)stack;
#endif // RT_ARM_V8M
    /* Exception return in all profiles will ignore the LSB of this field and
     * set the execution state based on the psr instead, but clear the LSB here
     * to match the behavior of exception entry, which does not set the LSB of
     * the exception return address. */
    ctx->r0 = arg;
    ctx->r1 = fn;
    ctx->pc = (uint32_t)rt_task_entry & ~UINT32_C(1);
    return ctx;
}

__attribute__((noreturn, weak)) void rt_idle(void)
{
    rt_task_drop_privilege();
    for (;;)
    {
        __asm__("wfi" :::);
    }
}

__attribute__((noreturn, weak)) void rt_abort(void)
{
    for (;;)
    {
        __asm__("udf" :::);
    }
}

__attribute__((noreturn, weak)) void rt_trap(void)
{
    for (;;)
    {
        __asm__("bkpt" :::);
    }
}

#if RT_ARM_V6M
#include "m/atomic-v6.c"
#endif