Require integer to specify callback interval with Ticker API

* Create new `s_timestamp_t` type to specify timestamp is seconds
* Alter `attach()` API to expect `s_timestamp_t` for interval value
* Create helper macro to convert seconds to milliseconds and help code
  readability
* Modify Greentea tests accordingly

TESTS/mbed_drivers/lp_ticker/main.cpp

@@ -142,7 +142,7 @@ void test_detach(void)
 {
     LowPowerTicker ticker;
     bool ret;
-    const float ticker_time_s = 0.1f;
+    const s_timestamp_t ticker_time_s = 1;
     const uint32_t wait_time_ms = 500;
     Semaphore sem(0, 1);
 
@@ -171,7 +171,7 @@ void test_attach_time(void)
 
     gtimer.reset();
     gtimer.start();
-    ticker.attach(callback(stop_gtimer_set_flag), ((float)DELAY_US) / 1000000.0f);
+    ticker.attach(callback(stop_gtimer_set_flag), MICROSECONDS_TO_SECONDS(DELAY_US));
     while (!ticker_callback_flag);
     ticker.detach();
     const int time_diff = gtimer.read_us();

TESTS/mbed_drivers/ticker/main.cpp

@@ -264,7 +264,7 @@ void test_detach(void)
 {
     Ticker ticker;
     bool ret;
-    const float ticker_time_s = 0.1f;
+    const s_timestamp_t ticker_time_s = 1;
     const uint32_t wait_time_ms = 500;
     Semaphore sem(0, 1);
 
@@ -293,7 +293,7 @@ void test_attach_time(void)
 
     gtimer.reset();
     gtimer.start();
-    ticker.attach(callback(stop_gtimer_set_flag), ((float)DELAY_US) / 1000000.0f);
+    ticker.attach(callback(stop_gtimer_set_flag), MICROSECONDS_TO_SECONDS(DELAY_US));
     while (!ticker_callback_flag);
     ticker.detach();
     const int time_diff = gtimer.read_us();

drivers/Ticker.h

@@ -78,9 +78,9 @@ public:
      *  @param func pointer to the function to be called
      *  @param t the time between calls in seconds
      */
-    void attach(Callback<void()> func, float t)
+    void attach(Callback<void()> func, const s_timestamp_t t)
     {
-        attach_us(func, t * 1000000.0f);
+        attach_us(func, SECONDS_TO_MICROSECONDS(t));
     }
 
     /** Attach a member function to be called by the Ticker, specifying the interval in seconds
@@ -96,10 +96,10 @@ public:
     MBED_DEPRECATED_SINCE("mbed-os-5.1",
                           "The attach function does not support cv-qualifiers. Replaced by "
                           "attach(callback(obj, method), t).")
-    void attach(T *obj, M method, float t)
-    {
-        attach(callback(obj, method), t);
-    }
+   void attach(T *obj, M method, float t)
+   {
+       attach(callback(obj, method), (s_timestamp_t)t);
+   }
 
     /** Attach a function to be called by the Ticker, specifying the interval in microseconds
      *

hal/ticker_api.h

@@ -24,6 +24,21 @@
 #include <stdbool.h>
 #include "device.h"
 
+/**
+ * Number of microseconds in a second
+ */
+#define MICROSECONDS_IN_SECOND  (us_timestamp_t)1000000
+
+/**
+ * Converts seconds to microseconds
+ */
+#define SECONDS_TO_MICROSECONDS(SECONDS)   (us_timestamp_t)(MICROSECONDS_IN_SECOND * SECONDS)
+
+/**
+ * Converts microseconds to seconds
+ */
+#define MICROSECONDS_TO_SECONDS(MICROSECONDS) (s_timestamp_t)(MICROSECONDS / MICROSECONDS_IN_SECOND)
+
 /**
  * Legacy format representing a timestamp in us.
  * Given it is modeled as a 32 bit integer, this type can represent timestamp
@@ -38,6 +53,11 @@ typedef uint32_t timestamp_t;
  */
 typedef uint64_t us_timestamp_t;
 
+/**
+ * A second timestamp stored in a 64 bit integer.
+ */
+typedef uint64_t s_timestamp_t;
+
 /** Ticker's event structure
  */
 typedef struct ticker_event_s {