AP_Scripting: add SD file and dataflash logging example

libraries/AP_Scripting/examples/logging.lua

@@ -0,0 +1,64 @@
+-- example of logging to a file on the SD card and to data flash
+local file_name = "AHRS_DATA.csv"
+local file
+
+-- index for the data and table
+local roll = 1
+local pitch = 2
+local yaw = 3
+local interesting_data = {}
+
+local function write_to_file()
+
+  if not file then
+    error("Could not open file")
+  end
+
+  -- write data
+  -- separate with comas and add a carriage return
+  file:write(tostring(millis()) .. ", " .. table.concat(interesting_data,", ") .. "\n")
+
+  -- make sure file is upto date
+  file:flush()
+
+end
+
+local function write_to_dataflash()
+
+  -- care must be taken when selecting a name, must be less than four characters and not clash with an existing log type
+  -- format characters specify the type of variable to be logged, see AP_Logger/README.md
+  -- not all format types are supported by scripting only: i, L, e, f, n, M, B, I, E, and N
+  -- lua automatically adds a timestamp in micro seconds
+  logger.write('SCR','roll(deg),pitch(deg),yaw(deg)','fff',interesting_data[roll],interesting_data[pitch],interesting_data[yaw])
+
+end
+
+function update()
+
+  -- get some interesting data
+  interesting_data[roll] = math.deg(ahrs:get_roll())
+  interesting_data[pitch] = math.deg(ahrs:get_pitch())
+  interesting_data[yaw] = math.deg(ahrs:get_yaw())
+
+  -- write to then new file the SD card
+  write_to_file()
+
+  -- write to a new log in the data flash log
+  write_to_dataflash()
+
+  return update, 1000 -- reschedules the loop
+end
+
+-- make a file
+-- note that this appends to the same the file each time, you will end up with a very big file
+-- you may want to make a new file each time using a unique name
+file = io.open(file_name, "a")
+if not file then
+  error("Could not make file")
+end
+
+-- write the CSV header
+file:write('Time Stamp(ms), roll(deg), pitch(deg), yaw(deg)\n')
+file:flush()
+
+return update, 10000