1 files changed, 106 insertions, 0 deletions
diff --git a/reference/C/CONTRIB/SNIP/uclock.c b/reference/C/CONTRIB/SNIP/uclock.c
new file mode 100755
index 0000000..0b0058c
--- /dev/null
+++ b/reference/C/CONTRIB/SNIP/uclock.c
@@ -0,0 +1,106 @@
+/*
+**  UCLOCK.C
+**
+**  Contains routines to perform microsecond accuracy timing
+**  operations.
+**
+**  Adapted from public domain source originally by David L. Fox
+**  Modified by Bob Stout
+*/
+
+#include "uclock.h"
+
+/* Constants */
+
+#define CONTVAL   0x34    /* == 00110100 Control byte for 8253 timer.   */
+                          /* Sets timer 0 to 2-byte read/write,         */
+                          /* mode 2, binary.                            */
+#define T0DATA    0x40    /* Timer 0 data port address.                 */
+#define TMODE     0x43    /* Timer mode port address.                   */
+#define BIOS_DS   0x40    /* BIOS data segment.                         */
+#define B_TIKP    0x6c    /* Address of BIOS (18.2/s) tick count.       */
+#define SCALE    10000    /* Scale factor for timer ticks.              */
+
+/* The following values assume 18.2 BIOS ticks per second resulting from
+   the 8253 being clocked at 1.19 MHz. */
+
+#define us_BTIK  54925    /* Micro sec per BIOS clock tick.             */
+#define f_BTIK    4595    /* Fractional part of usec per BIOS tick.     */
+#define us_TTIK   8381    /* Usec per timer tick * SCALE. (4/4.77 MHz)  */
+
+static int init = 0;
+
+/*
+**  usec_clock()
+**
+**  An analog of the clock() function, usec_clock() returns a number of
+**  type uclock_t (defined in UCLOCK.H) which represents the number of
+**  microseconds past midnight. Analogous to CLK_TCK is UCLK_TCK, the
+**  number which a usec_clock() reading must be divided by to yield
+**  a number of seconds.
+*/
+
+uclock_t usec_clock(void)
+{
+      unsigned char msb, lsb;
+      unsigned int tim_ticks;
+      static uclock_t last, init_count;
+      static uclock_t far *c_ptr;
+      uclock_t count, us_tmp;
+
+      if (!init)
+      {
+            c_ptr = (uclock_t far *)MK_FP(BIOS_DS, B_TIKP);
+            init  = 1;        /* First call, we have to set up timer.   */
+            int_off();
+            outp(TMODE, CONTVAL);   /* Write new control byte.          */
+            outp(T0DATA, 0);        /* Initial count = 65636.           */
+            outp(T0DATA, 0);
+            init_count = *c_ptr;
+            int_on();
+            return 0;               /* First call returns zero.         */
+      }
+
+      /* Read PIT channel 0 count - see text                            */
+
+      int_off();        /* Don't want an interrupt while getting time.  */
+      outp(TMODE, 0);                           /* Latch count.         */
+      lsb = (unsigned char)inp(T0DATA);         /* Read count.          */
+      msb = (unsigned char)inp(T0DATA);
+
+      /* Get BIOS tick count (read BIOS ram directly for speed and
+         to avoid turning on interrupts).                               */
+
+      count =  *c_ptr;
+      int_on();                     /* Interrupts back on.              */
+      if ((-1) == init)             /* Restart count                    */
+      {
+            init_count = count;
+            init = 1;
+      }
+
+      /* Merge PIT channel 0 count with BIOS tick count                 */
+
+      if (count < init_count)
+            count += last;
+      else  last = count;
+      count -= init_count;
+      tim_ticks = (unsigned)(-1) - ((msb << 8) | lsb);
+      us_tmp    = count * us_BTIK;
+      return (us_tmp + ((long)tim_ticks * us_TTIK + us_tmp % SCALE) / SCALE);
+}
+
+/*
+**  restart_uclock()
+**
+**  Since usec_clock() bases its return value on a differential value,
+**  a potential exists for problems in programs which run continuously
+**  for more than 24 hours. In such an application, it's necessary, at
+**  least once a day, to reset usec_clock's starting count.
+*/
+
+void restart_uclock(void)
+{
+      if (init)
+            init = -1;
+}