ardupilot/libraries/AP_HAL/Scheduler.h

#pragma once

#include <stdint.h>

#include <AP_Common/AP_Common.h>

#include "AP_HAL_Boards.h"
#include "AP_HAL_Namespace.h"


class AP_HAL::Scheduler {
public:
    Scheduler() {}
    virtual void     init() = 0;
    virtual void     delay(uint16_t ms) = 0;

    /*
      delay for the given number of microseconds. This needs to be as
      accurate as possible - preferably within 100 microseconds.
     */
    virtual void     delay_microseconds(uint16_t us) = 0;

    /*
      delay for the given number of microseconds. On supported
      platforms this boosts the priority of the main thread for a
      short time when the time completes. The aim is to ensure the
      main thread runs at a higher priority than drivers for the start
      of each loop
     */
    virtual void     delay_microseconds_boost(uint16_t us) { delay_microseconds(us); }

    /*
      inform the scheduler that we are calling an operation from the
      main thread that may take an extended amount of time. This can
      be used to prevent watchdog reset during expected long delays
      A value of zero cancels the previous expected delay
     */
    virtual void     expect_delay_ms(uint32_t ms) { }
    
    /*
      end the priority boost from delay_microseconds_boost()
     */
    virtual void     boost_end(void) {}

    // register a function to be called by the scheduler if it needs
    // to sleep for more than min_time_ms
    virtual void     register_delay_callback(AP_HAL::Proc,
                                             uint16_t min_time_ms);
    // returns true if the Scheduler has called the delay callback
    // function.  If you are on the main thread that means your call
    // stack has the scheduler on it somewhere.
    virtual bool     in_delay_callback() const { return _in_delay_callback; }

    // register a high priority timer task
    virtual void     register_timer_process(AP_HAL::MemberProc) = 0;

    // register a low priority IO task
    virtual void     register_io_process(AP_HAL::MemberProc) = 0;

    virtual void     register_timer_failsafe(AP_HAL::Proc,
                                             uint32_t period_us) = 0;

    virtual void     system_initialized() = 0;

    virtual void     reboot(bool hold_in_bootloader) = 0;

    /**
       optional function to stop clock at a given time, used by log replay
     */
    virtual void     stop_clock(uint64_t time_usec) {}

    virtual bool     in_main_thread() const = 0;

    /*
      disable interrupts and return a context that can be used to
      restore the interrupt state. This can be used to protect
      critical regions

      Warning: may not be implemented on all HALs
     */
    virtual void *disable_interrupts_save(void) { return nullptr; }

    /*
      restore interrupt state from disable_interrupts_save()
     */
    virtual void restore_interrupts(void *) {}

    // called by subclasses when they need to delay for some time
    virtual void call_delay_cb();
    uint16_t _min_delay_cb_ms;

    /*
      priority_base is used to select what the priority for a new
      thread is relative to
     */
    enum priority_base {
        PRIORITY_BOOST,
        PRIORITY_MAIN,
        PRIORITY_SPI,
        PRIORITY_I2C,
        PRIORITY_CAN,
        PRIORITY_TIMER,
        PRIORITY_RCIN,
        PRIORITY_IO,
        PRIORITY_UART,
        PRIORITY_STORAGE,
        PRIORITY_SCRIPTING,
    };
    
    /*
      create a new thread
     */
    virtual bool thread_create(AP_HAL::MemberProc proc, const char *name,
                               uint32_t stack_size, priority_base base, int8_t priority) {
        return false;
    }

private:

    AP_HAL::Proc _delay_cb;
    bool _in_delay_callback : 1;

};

/*
  helper macro and class to make using expect_delay_ms() safer and easier
 */
class ExpectDelay {
public:
    ExpectDelay(uint32_t ms);
    ~ExpectDelay();
};

#define EXPECT_DELAY_MS(ms) DELAY_JOIN( ms, __COUNTER__ )
#define DELAY_JOIN( ms, counter) _DO_DELAY_JOIN( ms, counter )
#define _DO_DELAY_JOIN( ms, counter ) ExpectDelay _getdelay ## counter(ms)