linux: Use Unix signals to notify when a timer is pending

Use Unix signals in software timer implementation.  This makes the
code a little more efficient.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/linux/internal.h

@@ -2,6 +2,7 @@
 #define __LINUX_INTERNAL_H
 // Local definitions for micro-controllers running on linux
 
+#include <signal.h> // sigset_t
 #include <stdint.h> // uint32_t
 #include "autoconf.h" // CONFIG_CLOCK_FREQ
 
@@ -10,7 +11,6 @@
 #define GPIO2PORT(PIN) ((PIN) / MAX_GPIO_LINES)
 #define GPIO2PIN(PIN) ((PIN) % MAX_GPIO_LINES)
 
-
 #define NSECS 1000000000
 #define NSECS_PER_TICK (NSECS / CONFIG_CLOCK_FREQ)
 
@@ -19,10 +19,12 @@ void report_errno(char *where, int rc);
 int set_non_blocking(int fd);
 int set_close_on_exec(int fd);
 int console_setup(char *name);
-void console_sleep(struct timespec ts);
+void console_sleep(sigset_t *sigset);
 
 // timer.c
 int timer_check_periodic(uint32_t *ts);
+void timer_disable_signals(void);
+void timer_enable_signals(void);
 
 // watchdog.c
 int watchdog_setup(void);