Add runtime and buildnml-time checks on output frequency

components/eamxx/cime_config/eamxx_buildnml.py

@@ -1017,6 +1017,23 @@ def do_cime_vars_on_yaml_output_files(case, caseroot):
             print ("  - setting skip_t0_output=true\n")
             print ("  - setting freq and freq_units to HIST_N and HIST_OPTION respectively\n")
 
+        # If frequency_units is not nsteps, verify that we don't request
+        # a frequency faster than the model timestep
+        if content['output_control']['frequency_units'] in ['nsecs','nmins','nhours']:
+            freq  = content['output_control']['Frequency']
+            units = content['output_control']['frequency_units']
+            dt_out = 1 if units=="nsecs" else 60 if units=="nmins" else 3600
+            dt_out = dt_out*int(freq)
+
+            dt_atm = 86400 / case.get_value("ATM_NCPL")
+            expect (dt_atm<=dt_out,
+                   "Cannot have output frequency faster than atm timestep.\n"
+                   f"   yaml file: {fn.strip()}\n"
+                   f"   Frequency: {freq}\n"
+                   f"   frequency_units: {units}\n"
+                   f"   ATM_NCPL: {case.get_value('ATM_NCPL')}\n"
+                   f" This yields dt_atm={dt_atm} > dt_output={dt_out}. Please, adjust 'Frequency' and/or 'frequency_units'\n")
+
         ordered_dump(content, open(dst_yaml, "w"))
 
         output_yaml_files.append(dst_yaml)

components/eamxx/src/share/io/scream_output_manager.cpp

@@ -328,6 +328,17 @@ void OutputManager::run(const util::TimeStamp& timestamp)
     return;
   }
 
+  // Ensure we did not go past the scheduled write time without hitting it
+  EKAT_REQUIRE_MSG (
+      (m_output_control.frequency_units=="nsteps"
+          ? timestamp.get_num_steps()<=m_output_control.next_write_ts.get_num_steps()
+          : timestamp<=m_output_control.next_write_ts),
+      "Error! The input timestamp is past the next scheduled write timestamp.\n"
+      "  - current time stamp   : " + timestamp.to_string() + "\n"
+      "  - next write time stamp: " + m_output_control.next_write_ts.to_string() + "\n"
+      "The most likely cause is an output frequency that is faster than the atm timestep.\n"
+      "Try to increase 'Frequency' and/or 'frequency_units' in your output yaml file.\n");
+
   // Update counters
   ++m_output_control.nsamples_since_last_write;
   ++m_checkpoint_control.nsamples_since_last_write;