AP_HAL: added EXPECT_DELAY() macro

this prevents nesting errors in use of EXPECT_DELAY(), ensuring we
always close the expected delay

libraries/AP_HAL/Scheduler.cpp

@@ -1,4 +1,5 @@
 #include "Scheduler.h"
+#include "AP_HAL.h"
 
 using namespace AP_HAL;
 
@@ -22,3 +23,13 @@ void Scheduler::call_delay_cb()
     _delay_cb();
     _in_delay_callback = false;
 }
+
+ExpectDelay::ExpectDelay(const AP_HAL::HAL &hal, uint32_t ms) : _hal(hal)
+{
+    _hal.scheduler->expect_delay_ms(ms);
+}
+
+ExpectDelay::~ExpectDelay()
+{
+    _hal.scheduler->expect_delay_ms(0);
+}

libraries/AP_HAL/Scheduler.h

@@ -121,3 +121,19 @@ private:
     bool _in_delay_callback : 1;
 
 };
+
+/*
+  helper macro and class to make using expect_delay_ms() safer and easier
+ */
+class ExpectDelay {
+public:
+    ExpectDelay(const AP_HAL::HAL &hal, uint32_t ms);
+    ~ExpectDelay();
+
+private:
+    const AP_HAL::HAL &_hal;
+};
+
+#define EXPECT_DELAY(hal, ms) DELAY_JOIN( hal, ms, __COUNTER__ )
+#define DELAY_JOIN( hal, ms, counter) _DO_DELAY_JOIN( hal, ms, counter )
+#define _DO_DELAY_JOIN( hal, ms, counter ) ExpectDelay _getdelay ## counter(hal, ms)