atspi-txrx can now send repeatedly, cleans up on ^C, prints the power level.

if it differs by more than 0.01 dBm from the level specified
- tools/atspi-txrx/Makefile (LDLIBS): added -lm, for fabs()
- tools/atspi-txrx/atspi-txrx.c (transmit, usage, main): add optional
  command-line argument with the number of times to send the message
- tools/atspi-txrx/atspi-txrx.c (receive, transmit, die, main): return and
  clean up on ^C
- tools/tools/lib/misctxrx.c (wait_for_interrupt) return and raise SIGINT
  for the caller's signal handler on ^C

tools/lib/misctxrx.c

@@ -15,19 +15,32 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
+#include <signal.h>
 
 #include "at86rf230.h"
 #include "atspi.h"
 #include "misctxrx.h"
 
 
+static volatile int run = 1;
+
+
+static void die(int sig)
+{
+	run = 0;
+}
+
+
 uint8_t wait_for_interrupt(struct atspi_dsc *dsc, uint8_t wait_for,
     uint8_t ignore, int sleep_us, int timeout)
 {
-	uint8_t irq, show;
+	uint8_t irq = 0, show;
+	void (*old_sig)(int);
 
-	while (1) {
-		while (!atspi_interrupt(dsc)) {
+	run = 1;
+	old_sig = signal(SIGINT, die);
+	while (run) {
+		while (run && !atspi_interrupt(dsc)) {
 			usleep(sleep_us);
 			if (timeout && !--timeout)
 				return 0;
@@ -57,5 +70,8 @@ uint8_t wait_for_interrupt(struct atspi_dsc *dsc, uint8_t wait_for,
 		if (irq & wait_for)
 			break;
 	}
+	signal(SIGINT, old_sig);
+	if (!run)
+		raise(SIGINT);
 	return irq;
 }