rom/kernel/kernel_timer.c

   1 /*
   2  * Generic support code for software emulated system timer.
   3  *
   4  * The main idea is: we have a single timer or arbitrary frequence (eclock),
   5  * which is used for generating timer interrupts. Its frequency can be higher
   6  * than reasonable VBlank frequency, so we emulate VBlank by dividing EClock
   7  * frequency by some integer factor.
   8  *
   9  * This code uses two variables in ExecBase, which describe the way in which the machine
  10  * measures time:
  11  *
  12  * VBlankFrequency    - this is the frequency with which exec VBlank handler is called.
  13  *                      Task scheduler's Quantum is measured in these intervals.
  14  * ex_EClockFrequency - this is the machine's master clock frequency. It specifies
  15  *                      how many EClock units is in one second. This value is provided
  16  *                      here to be used by generic software implementation of timer.device,
  17  *                      which simply counts ticks of our system timer. Real hardware
  18  *                      implementations of timer.device are expected to update ex_EClockFrequency
  19  *                      to the unit in which machine's hardware measures time.
  20  *
  21  * On native ports this file will likely be replaced by hardware-probing code.
  22  */
  23
  24 #include <aros/symbolsets.h>
  25 #include <exec/execbase.h>
  26 #include <hardware/intbits.h>
  27 #include <proto/arossupport.h>
  28 #include <proto/exec.h>
  29
  30 #include <kernel_base.h>
  31 #include <kernel_intr.h>
  32
  33 #include <stdlib.h>
  34 #include <string.h>
  35
  36 /* This definition can come from machine-specific files */
  37 #ifndef NO_VBLANK_EMU
  38
  39 static int Timer_Init(struct KernelBase *KernelBase)
  40 {
  41     char *args;
  42
  43     /*
  44      * This will make EClock frequency to be equal to VBlank by default.
  45      * Reasonable Amiga(tm)-compatible VBlank is already provided by exec.library.
  46      */
  47     SysBase->ex_EClockFrequency = 0;
  48
  49     /*
  50      * Since we are software-driven, we can just ask the user which
  51      * frequencies he wishes to use.
  52      */
  53     args = (char *)LibGetTagData(KRN_CmdLine, 0, BootMsg);
  54     if (args)
  55     {
  56         char *s;
  57
  58         /* Set VBlank and EClock frequencies if specified */
  59         s = strstr(args, "vblank=");
  60         if (s)
  61             SysBase->VBlankFrequency = atoi(&s[7]);
  62
  63         s = strstr(args, "eclock=");
  64         if (s)
  65             SysBase->ex_EClockFrequency = atoi(&s[7]);
  66     }
  67
  68     /* By default we enable VBlank emulation */
  69     KernelBase->kb_VBlankEnable = 1;
  70
  71     /*
  72      * Calculate number of timer ticks per VBlank and ensure that it is nonzero.
  73      * Note that if eclock= argument was not supplied this will set ticks
  74      * number to 1 (because ex_EClockFrequency is 0 by default).
  75      */
  76     KernelBase->kb_VBlankTicks = SysBase->ex_EClockFrequency / SysBase->VBlankFrequency;
  77     if (!KernelBase->kb_VBlankTicks)
  78         KernelBase->kb_VBlankTicks = 1;
  79
  80     /*
  81      * Calculate fixed up value of timer frequency. We need to set ex_EClockFrequency
  82      * in order to provide correct information to the software.
  83      * If timer.device provides better clock, it should update ex_EClockFrequency with
  84      * the value which reflects its time granularity.
  85      */
  86     SysBase->ex_EClockFrequency = SysBase->VBlankFrequency * KernelBase->kb_VBlankTicks;
  87
  88     return TRUE;
  89 }
  90
  91 ADD2INITLIB(Timer_Init, 0)
  92
  93 /* Handle periodic timer and drive exec VBlank */
  94 void core_TimerTick()
  95 {
  96     if (KernelBase->kb_VBlankEnable)
  97     {
  98         KernelBase->kb_TimerCount++;
  99         if (KernelBase->kb_TimerCount == KernelBase->kb_VBlankTicks)
 100         {
 101             core_Cause(INTB_VERTB, 1L << INTB_VERTB);
 102             KernelBase->kb_TimerCount = 0;
 103         }
 104     }
 105 }
 106
 107 #endif