Changeset c984fb3 in rtems

Timestamp:

05/22/04 15:14:31 (19 years ago)

Author:

Joel Sherrill <joel.sherrill@…>

Branches:

4.10, 4.11, 4.8, 4.9, 5, master

Children:

96e5865

Parents:

138aa38

Message:

2004-05-22 Till Strauman <strauman@…>

PR 619/bsps

• mpc6xx/clock/c_clock.c: The PPC decrementer must be reloaded on each clock tick. Currently, this is done by just reloading a fixed value. The attached patch takes into account the time that elapsed since the decrementer crossed zero in order to adjust the value to be re-loaded. Without the patch, the effective system clock cycle is increased by the exception handler latency.

Location:

c/src/lib/libcpu/powerpc

Files:

• ChangeLog (modified) (1 diff)
• mpc6xx/clock/c_clock.c (modified) (3 diffs)

c/src/lib/libcpu/powerpc/ChangeLog

@@ +1 @@
+2004-05-22      Till Strauman <strauman@slac.stanford.edu>
+
+        PR 619/bsps
+        * mpc6xx/clock/c_clock.c: The PPC decrementer must be reloaded on each
+        clock tick. Currently, this is done by just reloading a fixed value.
+        The attached patch takes into account the time that elapsed since the
+        decrementer crossed zero in order to adjust the value to be
+        re-loaded. Without the patch, the effective system clock cycle is
+        increased by the exception handler latency.
+
 2004-04-13      Ralf Corsepius <ralf_corsepius@rtems.org>
 

c/src/lib/libcpu/powerpc/mpc6xx/clock/c_clock.c

@@ -74 +74 @@
  *
  */
+
 void clockIsr()
 {
+int decr;
   /*
    *  The driver has seen another tick.
    */
-
-  PPC_Set_decrementer( Clock_Decrementer_value );
-
-  Clock_driver_ticks += 1;
-
-  /*
-   *  Real Time Clock counter/timer is set to automatically reload.
-   */
-
-  rtems_clock_tick();
+  do {
+        asm volatile ("mfdec %0; add %0, %0, %1; mtdec %0":"=r"(decr):"r"(Clock_Decrementer_value));
+
+        Clock_driver_ticks += 1;
+
+        /*
+         *  Real Time Clock counter/timer is set to automatically reload.
+         */
+        rtems_clock_tick();
+  } while ( decr < 0 );
 }
 
@@ -145 +147 @@
             (rtems_configuration_get_microseconds_per_tick()/1000);
 
+  /* set the decrementer now, prior to installing the handler 
+   * so no interrupts will happen in a while.
+   */
+  PPC_Set_decrementer( (unsigned)-1 );
+
+  /* if a decrementer exception was pending, it is cleared by
+   * executing the default (nop) handler at this point;
+   * The next exception will then be taken by our clock handler.
+   * Clock handler installation initializes the decrementer to
+   * the correct value.
+   */
+
   if (!BSP_connect_clock_handler ()) {
     printk("Unable to initialize system clock\n");
@@ -191 +205 @@
     else if (args->command == rtems_build_name('N', 'E', 'W', ' '))
     {
-      if (!BSP_connect_clock_handler ()) {
-        printk("Error installing clock interrupt handler!\n");
-        rtems_fatal_error_occurred(1);
-      }
+                Clock_initialize(major, minor, 0);
     }
 done: