Implement part of BmcEpoch

Add BmcEpoch which inherits EpochBase and will handle times for BMC,
it is partly implemented.

Add unit test cases to test basic functions.

Change-Id: Ia5e4d0f884156d238f3f84df490a2efbce43e89a
Signed-off-by: Lei YU <mine260309@gmail.com>
diff --git a/bmc_epoch.cpp b/bmc_epoch.cpp
new file mode 100644
index 0000000..c17ddf5
--- /dev/null
+++ b/bmc_epoch.cpp
@@ -0,0 +1,50 @@
+#include "bmc_epoch.hpp"
+
+#include <phosphor-logging/log.hpp>
+
+namespace phosphor
+{
+namespace time
+{
+namespace server = sdbusplus::xyz::openbmc_project::Time::server;
+using namespace phosphor::logging;
+
+BmcEpoch::BmcEpoch(sdbusplus::bus::bus& bus,
+                   const char* objPath)
+    : EpochBase(bus, objPath)
+{
+    // Empty
+}
+
+uint64_t BmcEpoch::elapsed() const
+{
+    // It does not needs to check owner when getting time
+    return getTime().count();
+}
+
+uint64_t BmcEpoch::elapsed(uint64_t value)
+{
+    // TODO: set time based on current time mode and owner
+    auto time = std::chrono::microseconds(value);
+    switch (timeOwner)
+    {
+        case Owner::BMC:
+        {
+            setTime(time);
+            break;
+        }
+        // TODO: below cases are to be implemented
+        case Owner::HOST:
+            break;
+        case Owner::SPLIT:
+            break;
+        case Owner::BOTH:
+            break;
+    }
+    server::EpochTime::elapsed(value);
+    return value;
+}
+
+}
+}
+