platform/minimal-net: Implement better idle behavior.

The minimal-net target, as currently written, wakes up the
CPU every millisecond to check for packets, and will only
react in real-time to input from stdin. If you are running
this on a laptop battery, your battery will quickly drain.

This change allows the CPU to idle when there is literally
nothing to do while still being responsive to input from
stein and/or incoming packets. This fix should significantly
improve performance while significantly improving power
usage. Win-win.

Also added `_xassert()` implementation so that the contiki-
provided `assert()` macro will work properly when used
on this platform.

cpu/native/net/tapdev-drv.c

@@ -59,7 +59,6 @@ tapdev_output(void)
 static void
 pollhandler(void)
 {
-  process_poll(&tapdev_process);
   uip_len = tapdev_poll();
 
   if(uip_len > 0) {

cpu/native/net/tapdev-drv.h

@@ -38,5 +38,6 @@
 PROCESS_NAME(tapdev_process);
 
 uint8_t tapdev_output(void);
+int tapdev_fd(void);
 
 #endif /* __TAPDEV_DRV_H__ */

cpu/native/net/tapdev.c

@@ -69,6 +69,13 @@ static unsigned long lasttime;
 
 #define BUF ((struct uip_eth_hdr *)&uip_buf[0])
 
+/*---------------------------------------------------------------------------*/
+int
+tapdev_fd(void)
+{
+  return fd;
+}
+
 /*---------------------------------------------------------------------------*/
 static void
 remove_route(void)

cpu/native/net/tapdev6.c

@@ -85,6 +85,13 @@ static unsigned long lasttime;
 static void do_send(void);
 uint8_t tapdev_send(uip_lladdr_t *lladdr);
 
+/*---------------------------------------------------------------------------*/
+int
+tapdev_fd(void)
+{
+  return fd;
+}
+
 
 uint16_t
 tapdev_poll(void)
@@ -161,6 +168,7 @@ tapdev_init(void)
   /*  gdk_input_add(fd, GDK_INPUT_READ,
       read_callback, NULL);*/
 
+  atexit(&tapdev_exit);
 }
 /*---------------------------------------------------------------------------*/
 static void

platform/minimal-net/contiki-main.c

@@ -33,13 +33,16 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
 #include <time.h>
 #include <sys/select.h>
 #include <unistd.h>
 #include <memory.h>
 
 #include "contiki.h"
 #include "contiki-net.h"
+#include "lib/assert.h"
 
 #include "dev/serial-line.h"
 
@@ -267,9 +270,15 @@ main(void)
        (ipaddr.u16[2] != 0) ||
        (ipaddr.u16[3] != 0)) {
 #if UIP_CONF_ROUTER
-      uip_ds6_prefix_add(&ipaddr, UIP_DEFAULT_PREFIX_LEN, 0, 0, 0, 0);
+      if(!uip_ds6_prefix_add(&ipaddr, UIP_DEFAULT_PREFIX_LEN, 0, 0, 0, 0)) {
+        fprintf(stderr,"uip_ds6_prefix_add() failed.\n");
+        exit(EXIT_FAILURE);
+      }
 #else /* UIP_CONF_ROUTER */
-      uip_ds6_prefix_add(&ipaddr, UIP_DEFAULT_PREFIX_LEN, 0);
+      if(!uip_ds6_prefix_add(&ipaddr, UIP_DEFAULT_PREFIX_LEN, 0)) {
+        fprintf(stderr,"uip_ds6_prefix_add() failed.\n");
+        exit(EXIT_FAILURE);
+      }
 #endif /* UIP_CONF_ROUTER */
 
       uip_ds6_set_addr_iid(&ipaddr, &uip_lladdr);
@@ -290,36 +299,66 @@ main(void)
 
 #if UIP_CONF_IPV6 && !RPL_BORDER_ROUTER  /* Border router process prints addresses later */
   {
-    uint8_t i;
+    int i = 0;
+    int interface_count = 0;
     for(i = 0; i < UIP_DS6_ADDR_NB; i++) {
       if(uip_ds6_if.addr_list[i].isused) {
-	printf("IPV6 Addresss: ");
-	sprint_ip6(uip_ds6_if.addr_list[i].ipaddr);
-	printf("\n");
+        printf("IPV6 Addresss: ");
+        sprint_ip6(uip_ds6_if.addr_list[i].ipaddr);
+        printf("\n");
+        interface_count++;
       }
     }
+    assert(0 < interface_count);
   }
 #endif
 
   while(1) {
     fd_set fds;
     int n;
     struct timeval tv;
+    clock_time_t next_event;
 
     n = process_run();
+    next_event = etimer_next_expiration_time() - clock_time();
+
+#if DEBUG_SLEEP
+    if(n > 0)
+      printf("sleep: %d events pending\n",n);
+    else
+      printf("sleep: next event @ T-%.03f\n",(double)next_event / (double)CLOCK_SECOND);
+#endif
+
+#ifdef __CYGWIN__
+    /* wpcap doesn't appear to support select, so
+     * we can't idle the process on windows. */
+    next_event = 0;
+#endif
+
+    if(next_event > (CLOCK_SECOND * 2))
+      next_event = CLOCK_SECOND * 2;
+    tv.tv_sec = n ? 0 : (next_event / CLOCK_SECOND);
+    tv.tv_usec = n ? 0 : ((next_event % 1000) * 1000);
 
-    tv.tv_sec = 0;
-    tv.tv_usec = 1000;
     FD_ZERO(&fds);
     FD_SET(STDIN_FILENO, &fds);
+#ifdef __CYGWIN__
     select(1, &fds, NULL, NULL, &tv);
+#else
+    FD_SET(tapdev_fd(), &fds);
+    if(0 > select(tapdev_fd() + 1, &fds, NULL, NULL, &tv)) {
+      perror("Call to select() failed.");
+      exit(EXIT_FAILURE);
+    }
+#endif
 
     if(FD_ISSET(STDIN_FILENO, &fds)) {
       char c;
       if(read(STDIN_FILENO, &c, 1) > 0) {
 	serial_line_input_byte(c);
       }
     }
+    process_poll(&tapdev_process);
     etimer_request_poll();
   }
 
@@ -338,6 +377,14 @@ uip_log(char *m)
   printf("uIP: '%s'\n", m);
 }
 /*---------------------------------------------------------------------------*/
+void
+_xassert(const char *file, int line)
+{
+  fprintf(stderr, "%s:%u: failed assertion\n", file, line);
+  abort();
+}
+
+
 unsigned short
 sensors_light1(void)
 {