Adds design document for Omega driver layer

components/omega/doc/design/Driver.md

@@ -0,0 +1,253 @@
+(omega-design-driver)=
+# Driver and Component Layer
+
+## 1 Overview
+
+OMEGA can be used as either a standalone ocean model or as
+the ocean component of E3SM. In either case, OMEGA requires a
+top-level driver and interface layer. Here we describe the
+requirements and design of both the standalone driver (main)
+and the component interface for coupled simulation.
+
+## 2 Requirements
+
+### 2.1 Requirement: Component interfaces
+
+When running as part of a larger coupled model, OMEGA must
+supply initialize, run and finalize methods. These routines
+must export all variables needed by the parent model while also
+importing all fields needed by OMEGA. In most cases, there will
+also need to be a thin wrapper to translate data types between
+the parent model and internal OMEGA data types.
+
+### 2.2 Requirement: Standalone driver
+
+When OMEGA is used as a standalone model, it must supply a
+driver or main routine. For consistency with coupled
+simulations, this driver must mimic a parent coupled model,
+calling the same init, run and finalize methods and supplying
+any needed data (eg surface forcing data).
+
+### 2.3 Requirement: Encapsulation and persistent model state
+
+Communication with the parent model or standalone driver must
+be through the component interfaces as method arguments. All
+other aspects of the OMEGA model and model state that need to
+be retained across component calls or subsequent run intervals
+must be stored internally within OMEGA as static variables.
+
+### 2.4 Requirement: Managing environments
+
+Initializing and exiting environments like MPI and YAKL must
+take place at the driver level (standalone driver or coupled
+model driver) as these environments are shared by other
+components. The finalize method described below must clean up
+all of Omega memory and data types so that these environments
+can be exited cleanly.
+
+### 2.5 Requirement: Run method
+
+The run method must advance the model one specified time
+interval based on a set of inputs (the import state) and must
+return a set of outputs (the export state) at the end of the
+time interval. In a coupled simulation, this interval will be
+the coupling interval. In standalone simulations, this interval
+is typically the fastest forcing data interval.
+
+### 2.6 Requirement: Finalize method
+
+The finalize method must provide a graceful exit, checkpointing
+as needed and cleaning up all memory. It must not, however,
+exit the MPI or other shared environments (eg YAKL) per
+requirement 2.4
+
+### 2.7 Requirement: Init method
+
+An initialization method must initialize all model state, mesh
+and other information needed by the model itself or the parent
+coupled system. The model state must correspond to the initial
+time for the simulation integration.
+
+## 3 Algorithmic Formulation
+
+No algorithms are introduced.
+
+## 4 Design
+
+The design is essentially determined by the requirements above.
+We define an init, run and finalize method. There will actually
+be two layers of these functions. One will be the internal
+Omega inteface used by the Omega standalone driver. A second
+layer will be needed for translating between internal Omega
+data types and E3SM (or other parent model) data types and
+ensuring the model is synchronized correctly with the parent. 
+
+Within the directory structure of OMEGA, the `src/driver`
+directory will contain two subdirectories called standalone
+and E3SM. The standalone subdirectory will contain the
+standalone driver (obviously) and the E3SM directory will
+contain the wrapper interfaces that translate between the
+E3SM components and data types and the Omega methods and data
+types. The CMake build system will determine which directory
+will be used in the build. The actual OcnInit, OcnRun, OcnFinalize
+routines described below will reside in the `src/ocean` directory.
+
+### 4.1 Data types and parameters
+
+#### 4.1.1 Parameters
+
+There are currently no additional parameters needed for this level. Configuration is generally determined by other modules.
+
+#### 4.1.2 Class/structs/data types
+
+For standalone simulation, data types are determined by other modules (eg state and mesh). No new data types are needed here.
+
+E3SM data types are in flux (from MCT to MOAB). We will add the coupled model data types here in the future. 
+
+### 4.2 Methods
+
+#### 4.2.1 Init
+
+The Init method (OcnInit) will call individual initialization
+routines for every module in Omega. On input, it requires the
+MPI communicator to use as the master ocean communicator
+(`MPI_COMM_WORLD` for standalone, a coupler-partitioned
+communicator for coupled simulations). On output, it will
+return mesh information, the current model state and the
+time instant associated with that state. 
+
+The precise interface awaits the design of various other
+modules, but will look something like:
+```c++
+int OMEGA::OcnInit(
+   MPIComm Comm, ///< [in] ocean MPI communicator
+   OMEGA::TimeInstant &StartTime, ///< [out] sim start time
+   OMEGA::TimeInterval &RunInterval, ///< [out] interval for run method
+   OMEGA::State &CurrState, ///< [out] current model state
+   other args as needed
+);
+```
+The routine will return the initial state, the start time and
+the run interval computed based on input options. An integer
+return value will be non-zero if errors are encountered and zero
+if successful.
+It is also possible that a multi-stage initialization may
+be needed, especially in coupled mode and would require
+additional OcnInit interfaces. This will be determined during
+integration with E3SM later.
+
+#### 4.2.2 Run
+
+The run method will advance the model one time interval,
+typically the coupling time or the fastest forcing interval.
+The interface will look like:
+```c++
+int OMEGA::OcnRun(
+   OMEGA::TimeInstant &CurrTime, ///< [inout] current sim time
+   OMEGA::TimeInterval &RunInterval, ///< [in] interval to advance model
+   OMEGA::Alarm &EndAlarm, ///< [out] alarm to end simulation
+   OMEGA::State &CurrState, ///< [inout] current model state
+   other args as needed (eg forcing)
+)
+```
+The model state, current time and the time interval will be input.
+Other variables will be needed as well, like the surface forcing
+fields, and will be added as needed. On return, the time instant
+will contain the end time of the interval and the end alarm will
+be ringing if the end of the simulation has been reached. The
+CurrState will be the ocean state at the end of the run interval.
+An integer error code will be zero if successful and non-zero if an
+error was encountered. This interface will be modified as needed to
+include other fields.
+
+#### 4.2.3 Finalize
+
+The finalize method will write a checkpoint/restart file
+(if not already written by driver or run method on the
+final timestep) and then clean up all arrays and classes by
+calling the relevant routines for all Omega modules. The
+interface is similar to the Init interface:
+
+```c++
+int OMEGA::OcnFinalize(
+   OMEGA::TimeInstant &CurrTime, ///< [in] current sim time
+   OMEGA::State &CurrState, ///< [in] current model state
+   other args as needed for restart
+);
+```
+An integer return value will be zero if successful and
+non-zero if an error is encountered either writing a
+restart or deallocating memory.
+
+#### 4.2.4 Standalone driver (main)
+
+With the interfaces above, the standalone driver should look
+something like the code below (details subject to change during implementation).
+```c++
+
+int main(int argc, char **argv) {
+
+   MPI_Init(); // initialize MPI
+   yakl::init(); // initialize YAKL
+
+   OMEGA::State CurrState;
+   OMEGA::TimeInstant CurrTime;
+   OMEGA::TimeInterval RunInterval;
+   OMEGA::Alarm EndAlarm;
+
+   int Err = OcnInit(MPI_COMM_WORLD, CurrTime, RunInterval, CurrState,
+                     etc);
+   if (Err != 0) LOG_ERROR("Error initializing OMEGA");
+
+
+   while (Err == 0 && !(EndAlarm.isRinging()) ) {
+
+      // call routines for forcing and other inputs
+
+      // call run method
+      Err = OMEGA::OcnRun(CurrTime, RunInterval, EndAlarm,
+                          CurrState, etc);
+      if (Err != 0) LOG_ERROR("Error advancing Omega one interval");
+
+      // Other tasks if needed (eg IO could occur here or within run
+      // method
+   }
+
+   int Err2 = OMEGA::OcnFinalize(CurrTime, CurrState, etc);
+   if (Err2 != 0) LOG_ERROR("Error finalizing Omega");
+
+   int ErrAll = abs(Err) + abs(Err2);
+   if (ErrAll == 0){
+      LOG_INFO("OMEGA successfully completed");
+   } else {
+      LOG_ERROR("OMEGA terminating due to error");
+   }
+
+   // Exit various environments
+   yakl::finalize();
+   MPI::Finalize();
+
+   return ErrAll;
+}
+
+```
+
+#### 4.2.5 Coupler-component interfaces
+
+To be added later
+
+## 5 Verification and Testing
+
+### 5.1 Test forward model
+
+A forward model test is included as part of the test suite
+that runs the standalone model and tests for successful
+completion. All forward model system testing will be
+inherently testing the driver.
+  - tests requirements 2.2-2.7
+
+### 5.2 Coupled model testing
+
+Once Omega is integrated into E3SM, various E3SM tests will
+be run regularly and will test all interfaces
+  - tests requirement 2.1

components/omega/doc/index.md

@@ -54,6 +54,7 @@ design/Broadcast
 design/Config
 design/DataTypes
 design/Decomp
+design/Driver
 design/Halo
 design/Logging
 design/MachEnv