galileo: Support for rtimer library

This patch adds support for rtimer library on Galileo's platform.

We use the PIT to implement the rtimer platform dependent
functionalities. We chose the PIT for mainly two reason: I) its
configuration is very simple II) it has a high frequency which
provides us a good clock resolution (requirement from rtimer
library).

Since we keep track of the number of ticks in software, we define
rtimer_clock_t type as uint64_t. This gives us a good amount of time
til the variable overflows. For instance, a 32-bit type would overflow
in about one hour for high clock resolution (~ 1us).

The rtimer clock frequency (RTIMER_ARCH_SECOND) is setup to 1 kHz.
There is no technical matter regarding this value. It is just an
initial guess.

Just for the record, we might want to use HPET in future to
implement the rtimer library since it seems to be more appropriate.
The reason why we don't use it at this moment is that, in order to
configure it, we need support for ACPI 2.0 which we don't. Once we
have use-cases for the rtimer library we'll probably replace PIT
by HPET or any other timer more suitable for the job.

platform/galileo/Makefile.galileo

@@ -3,7 +3,7 @@ LIBGCC_PATH = /usr/lib/gcc/$(shell gcc -dumpmachine)/$(shell gcc -dumpversion)
 
 CONTIKI_TARGET_DIRS = .
 CONTIKI_TARGET_MAIN = ${addprefix $(OBJECTDIR)/,contiki-main.o}
-CONTIKI_SOURCEFILES += contiki-main.c newlib-syscalls.c loader.S clock.c
+CONTIKI_SOURCEFILES += contiki-main.c newlib-syscalls.c loader.S clock.c rtimer-arch.c
 
 LINKERSCRIPT = $(CONTIKI)/platform/galileo/galileo.ld
 

platform/galileo/contiki-conf.h

@@ -36,6 +36,10 @@
 #define CLOCK_CONF_SECOND 128
 typedef unsigned long clock_time_t;
 
+typedef uint64_t rtimer_clock_t;
+#define RTIMER_ARCH_SECOND 1024
+#define RTIMER_CLOCK_LT(a, b)     ((int64_t)((a) - (b)) < 0)
+
 /* We define the following macros and types otherwise Contiki does not
  * compile.
  */

platform/galileo/contiki-main.c

@@ -37,6 +37,7 @@ main(void)
 {
   cpu_init();
   clock_init();
+  rtimer_init();
 
   ENABLE_IRQ();
 

platform/galileo/rtimer-arch.c

@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2015, Intel Corporation. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * 3. Neither the name of the copyright holder nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "sys/rtimer.h"
+
+#include "contiki-conf.h"
+#include "drivers/pit.h"
+
+static volatile rtimer_clock_t tick_count = 0;
+static rtimer_clock_t trigger = UINT64_MAX;
+
+static void
+update_ticks(void)
+{
+  if(++tick_count >= trigger) {
+    /* Disable trigger by assigning it to the maximum value */
+    trigger = UINT64_MAX;
+    rtimer_run_next();
+  }
+}
+/*---------------------------------------------------------------------------*/
+void
+rtimer_arch_init(void)
+{
+  pit_init(RTIMER_ARCH_SECOND, update_ticks);
+}
+/*---------------------------------------------------------------------------*/
+rtimer_clock_t
+rtimer_arch_now()
+{
+  return tick_count;
+}
+/*---------------------------------------------------------------------------*/
+void
+rtimer_arch_schedule(rtimer_clock_t t)
+{
+  trigger = t;
+}

platform/galileo/rtimer-arch.h

@@ -31,4 +31,6 @@
 #ifndef RTIMER_ARCH_H
 #define RTIMER_ARCH_H
 
+rtimer_clock_t rtimer_arch_now();
+
 #endif /* RTIMER_ARCH_H */