Merge pull request #1961 from ghaerr/prectimer2

[kernel] Finalize precision timing routines

elks/arch/i86/lib/prectimer.c

@@ -41,6 +41,7 @@ static unsigned long lastjiffies;
  * unsigned long jiffies        jiffies   497 days(< 2^32 jiffies)
  */
 
+#if 0   /* don't use - too unreliable with no overflow check */
 /* read PIT diff count, returns < 11932 pticks (10ms), no overflow checking */
 unsigned int get_time_10ms(void)
 {
@@ -58,20 +59,32 @@ unsigned int get_time_10ms(void)
     lastcount = count;
     return pdiff;
 }
+#endif
 
 /* count up to 5 jiffies in pticks, returns < 59660 pticks (50ms), w/overflow check */
 unsigned int get_time_50ms(void)
 {
-    int jdiff;
-    unsigned int pticks;
+    int pticks, jdiff;
+    unsigned int lo, hi, count;
+    flag_t flags;
+    static unsigned int lastcount;
 
-    clr_irq();
+    save_flags(flags);
+    clr_irq();                      /* synchronize countdown and jiffies */
+    outb(0, TIMER_CMDS_PORT);       /* latch timer value */
+    /* ia16-elf-gcc won't generate 32-bit subtract so use 16-bit and check wrap */
     jdiff = (unsigned)jiffies - (unsigned)lastjiffies;
     lastjiffies = jiffies;          /* 32 bit save required after ~10.9 mins */
-    outb(0, TIMER_CMDS_PORT);       /* latch timer value */
-    set_irq();
+    restore_flags(flags);
+
+    lo = inb(TIMER_DATA_PORT);
+    hi = inb(TIMER_DATA_PORT) << 8;
+    count = lo | hi;
+    pticks = lastcount - count;
+    if (pticks < 0)                 /* wrapped */
+        pticks += MAX_PTICK;        /* = MAX_PTICK - count + lastcount */
+    lastcount = count;
 
-    pticks = get_time_10ms();
     if (jdiff < 0)                  /* lower half wrapped */
         jdiff = -jdiff;             /* = 0x10000000 - lastjiffies + jiffies */
     if (jdiff >= 2) {
@@ -88,8 +101,7 @@ unsigned long get_time(void)
     unsigned int pticks;
     static unsigned long lasttime;
 
-    clr_irq();                  /* for saving lasttime below */
-    lasttime = lastjiffies;
+    lasttime = lastjiffies;     /* race condition here before clr_irq in get_time_50ms */
     pticks = get_time_50ms();
     if (pticks != 0)
         return pticks;          /* < 50ms */
@@ -99,13 +111,15 @@ unsigned long get_time(void)
 
 #if TIMER_TEST
 /* sample timer routines */
+#if 0
 void timer_10ms(void)
 {
     unsigned int pticks;
 
     pticks = get_time_10ms();
     printk("%u %u = %k\n", pticks, (unsigned)jiffies, pticks);
 }
+#endif
 
 void timer_50ms(void)
 {

elks/init/main.c

@@ -88,11 +88,21 @@ static void INITPROC early_kernel_init(void);
 #if TIMER_TEST
 void testloop(unsigned timer)
 {
-        unsigned pticks, x = timer;
-
-        get_time_10ms();
-        while (x--) outb(x, 0x80);
-        pticks = get_time_10ms();
+        unsigned int pticks, x = timer;
+        int i;
+        static unsigned int a[10];
+
+#if 1
+        get_time_50ms();
+        for (i=0; i<10; i++)
+            a[i] = get_time_50ms();
+        for (i=0; i<10; i++)
+            printk("%d,", a[i]);
+        printk("\n");
+#endif
+        get_time_50ms();
+        while (x--) asm("nop");
+        pticks = get_time_50ms();
         printk("hptimer %u: %k (%u)\n", timer, pticks, pticks);
 }
 #endif
@@ -107,30 +117,28 @@ void start_kernel(void)
     setsp(&task->t_regs.ax);    /* change to idle task stack */
     kernel_init();              /* continue init running on idle task stack */
 
+#if TIMER_TEST
+    /* run tests before 2nd process created for stability */
+    testloop(30000);
+    testloop(3000);
+    testloop(300);
+    printk("\n");
+#endif
+
     /* fork and run procedure init_task() as task #1*/
     kfork_proc(init_task);
     wake_up_process(&task[1]);
 
     /*
      * We are now the idle task. We won't run unless no other process can run.
      */
-#if TIMER_TEST
-    timer_test();
-    testloop(10000);
-    testloop(3000);
-    testloop(500);
-#endif
     while (1) {
-#if TIMER_TEST
-        timer_50ms();
-#else
         schedule();
 #ifdef CONFIG_TIMER_INT0F
         int0F();        /* simulate timer interrupt hooked on IRQ 7 */
 #else
         idle_halt();    /* halt until interrupt to save power */
 #endif
-#endif /* TIMER_TEST */
     }
 }
 

qemu.sh

@@ -118,6 +118,9 @@ AUDIO="-audiodev pa,id=speaker -machine pcspk-audiodev=speaker"
 
 # Configure QEMU as pure ISA system
 
-exec $QEMU $AUDIO $CONSOLE -nodefaults -name ELKS -machine isapc -cpu 486,tsc -m 4M \
+# uncomment to run native speed if x86 macOS
+#MACOS="-accel hvf"
+
+exec $QEMU $MACOS $AUDIO $CONSOLE -nodefaults -name ELKS -machine isapc -cpu 486,tsc -m 4M \
 $KEYBOARD $QDISPLAY -vga std -rtc base=utc $SERIAL \
 $NET $NETDUMP $IMAGE $DISK2 $@