some fixes

focus_seq_FLI.py

@@ -21,7 +21,7 @@ import pathlib as pl
 
 
 def init_seq(seq_kwds):
-    # replace extension as Eddy's 'fli_control' add hardcoded '.fit'
+    # replace extension since Eddy's 'fli_control' adds hardcoded '.fit'
     pt = pl.Path(seq_kwds["root_filename"]).with_suffix(".fit")
     seq_kwds["root_filename"] = str(pt)
 
@@ -47,6 +47,10 @@ def init_seq(seq_kwds):
 
 
 def set_focus(foc_val):
+    if foc_val < 0:
+        print("INVALID FLI-FOCUSER VALUE! IT MUST BE NON-NEGATIVE VALUE!")
+        return -1
+
     cmd = ["fli_control", "-g", str(int(foc_val))]
     ret = sp.run(cmd, stdout=sp.PIPE, stderr=sp.PIPE)
     return ret.returncode