kern_idlethread.cxx

C++ 编写的EROS RTOS

/*
 * Copyright (C) 1998, 1999, Jonathan S. Shapiro.
 *
 * This file is part of the EROS Operating System.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2,
 * or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include <kerninc/kernel.hxx>
#include <kerninc/Thread.hxx>
#include <kerninc/CpuReserve.hxx>
#include <kerninc/Machine.hxx>

const uint32_t StackSize = 256;
static uint32_t Stack[StackSize];

/* I wonder
 * if I shouldn't hand-code this thread in assembler for the sake of
 * reducing it's stack, though.
 */

class IdleThread : public KernThread {
public:
  static void Start();

  IdleThread()
    :KernThread("Idler", 
		&IdleThread::Start,
		Stack, &Stack[StackSize])
  {
    procContext.InitStack();
  }
};

IdleThread TheIdleThread;
Thread *pIdleThread = &TheIdleThread;

void 
StartIdleThread()
{
  CpuReserve::KernIdleCpuReserve.AddKernelThread(&TheIdleThread);
  TheIdleThread.Wakeup();	/* let it initialize itself... */
  
  printf("IdleThread...\n");
}

/* Unlike all other threads, this one runs once and then exits (or at
 * least sleeps forever).
 */
void
IdleThread::Start()
{
  int stack;
  printf("Start IdleThread (thread 0x%x,context 0x%x,stack 0x%x)\n",
	       &TheIdleThread, TheIdleThread.context, &stack);

  for(;;) {
    /* On machines with high privilege-crossing latency, it is NOT a
     * good idea for the idle thread to enter and leave the kernel
     * aggressively.  On the x86, for example, this can easily render
     * the processor non-interruptable for 300-400 cycles PER YIELD,
     * which (among other problems) has the effect of quantizing
     * interrupt response time. 
     *    Machine::SpinWaitUs(50);
     */
    TheIdleThread.DirectedYield();
#if 0
    Console::Twiddle(0);
#endif
  }

    /* We will never wake up again... */
  TheIdleThread.SleepOn(IdlePile);
  TheIdleThread.DirectedYield();
}