Timer driver: Add hooks to support signal notification of timer expiration. Commented out because invasive interface changes would also be required to complete the implementation.

drivers/timers/timer.c

@@ -66,6 +66,11 @@
 struct timer_upperhalf_s
 {
   uint8_t   crefs;         /* The number of times the device has been opened */
+#ifdef HAVE_NOTIFICATION
+  uint8_t   signal;        /* The signal number to use in the notification */
+  pid_t     pid;           /* The ID of the task/thread to receive the signal */
+  FAR void *arg;           /* An argument to pass with the signal */
+#endif
   FAR char *path;          /* Registration path */
 
   /* The contained lower-half driver */
@@ -77,6 +82,12 @@ struct timer_upperhalf_s
  * Private Function Prototypes
  ****************************************************************************/
 
+#ifdef HAVE_NOTIFICATION
+  /* REVISIT: This function prototype is insufficient to support signaling */
+
+static bool    timer_notifier(FAR uint32_t *next_interval_us);
+#endif
+
 static int     timer_open(FAR struct file *filep);
 static int     timer_close(FAR struct file *filep);
 static ssize_t timer_read(FAR struct file *filep, FAR char *buffer,
@@ -110,6 +121,36 @@ static const struct file_operations g_timerops =
  * Private Functions
  ****************************************************************************/
 
+/************************************************************************************
+ * Name: timer_notifier
+ *
+ * Description:
+ *   Notify the application via a signal when the timer interrupt occurs
+ *
+ * REVISIT: This function prototype is insufficient to support signaling
+ *
+ ************************************************************************************/
+
+#ifdef HAVE_NOTIFICATION
+static bool timer_notifier(FAR uint32_t *next_interval_us)
+{
+  FAR struct timer_upperhalf_s *upper = HOW?;
+#ifdef CONFIG_CAN_PASS_STRUCTS
+  union sigval value;
+#endif
+  int ret;
+
+#ifdef CONFIG_CAN_PASS_STRUCTS
+  value.sival_ptr = upper->arg;
+  ret = sigqueue(upper->pid, upper->signo, value);
+#else
+  ret = sigqueue(upper->pid, upper->signo, upper->arg);
+#endif
+
+  return ret == OK;
+}
+#endif
+
 /************************************************************************************
  * Name: timer_open
  *
@@ -322,6 +363,36 @@ static int timer_ioctl(FAR struct file *filep, int cmd, unsigned long arg)
       }
       break;
 
+#ifdef HAVE_NOTIFICATION
+    /* cmd:         TCIOC_NOTIFICATION
+     * Description: Notify application via a signal when the timer expires.
+     * Argument:    signal number
+     *
+     * NOTE: This ioctl cannot be support in the kernel build mode. In that
+     * case direct callbacks from kernel space into user space is forbidden.
+     */
+
+    case TCIOC_NOTIFICATION:
+      {
+        FAR struct timer_notify_s *notify =
+          (FAR struct timer_notify_s *)((uintptr_t)arg)
+
+        if (notify != NULL)
+          {
+            upper->signo = notify->signal;
+            upper->get   = notify->signal;
+            upper->arg   = noify->arg;
+
+            ret = timer_sethandler((FAR void *handle)upper, timer_notifier, NULL);
+          }
+        else
+          {
+            ret = -EINVAL;
+          }
+      }
+      break;
+#endif
+
     /* Any unrecognized IOCTL commands might be platform-specific ioctl commands */
 
     default:

include/nuttx/timers/timer.h

@@ -52,6 +52,12 @@
 /****************************************************************************
  * Pre-processor Definitions
  ****************************************************************************/
+/* It would require some interface modifcations in order to support
+ * notifications.
+ */
+
+#undef HAVE_NOTIFICATION
+
 /* IOCTL Commands ***********************************************************/
 /* The timer driver uses a standard character driver framework.  However,
  * since the timer driver is a device control interface and not a data
@@ -68,6 +74,10 @@
  *                      Argument:  A writeable pointer to struct timer_status_s.
  * TCIOC_SETTIMEOUT   - Reset the timer timeout to this value
  *                      Argument: A 32-bit timeout value in microseconds.
+ * TCIOC_NOTIFICATION - Set up to notify an application via a signal when
+ *                      the timer expires.
+ *                      Argument: A read-only pointer to an instance of
+ *                      stuct timer_notify_s.
  *
  * WARNING: May change TCIOC_SETTIMEOUT to pass pointer to 64bit nanoseconds
  * or timespec structure.
@@ -86,7 +96,9 @@
 #define TCIOC_STOP         _TCIOC(0x0002)
 #define TCIOC_GETSTATUS    _TCIOC(0x0003)
 #define TCIOC_SETTIMEOUT   _TCIOC(0x0004)
-#define TCIOC_SETHANDLER _TCIOC(0x0005)
+#ifdef HAVE_NOTIFICATION
+#define TCIOC_NOTIFICATION _TCIOC(0x0005)
+#endif
 
 /* Bit Settings *************************************************************/
 /* Bit settings for the struct timer_status_s flags field */
@@ -117,6 +129,17 @@ struct timer_status_s
                              * (in microseconds) */
 };
 
+#ifdef HAVE_NOTIFICATION
+/* This is the type of the argument passed to the TCIOC_NOTIFICATION ioctl */
+
+struct timer_notify_s
+{
+  FAR void *arg;            /* An argument to pass with the signal */
+  pid_t     pid;            /* The ID of the task/thread to receive the signal */
+  uint8_t   signal;         /* The signal number to use in the notification */
+};
+#endif
+
 /* This structure provides the "lower-half" driver operations available to
  * the "upper-half" driver.
  */