AP_Scripting: added rc:get_aux_cached() example

libraries/AP_Scripting/examples/aux_cached.lua

@@ -0,0 +1,37 @@
+--[[ 
+   example for getting cached aux function value
+--]]
+
+local RATE_HZ = 10
+
+local MAV_SEVERITY_ERROR = 3
+local MAV_SEVERITY_INFO = 6
+
+local AUX_FUNCTION_NUM = 302
+
+local last_func_val = nil
+local last_aux_pos = nil
+
+function update()
+   local aux_pos = rc:get_aux_cached(AUX_FUNCTION_NUM)
+   if aux_pos ~= last_aux_pos then
+      last_aux_pos = aux_pos
+      gcs:send_text(MAV_SEVERITY_INFO, string.format("Aux set to %u", aux_pos))
+   end
+end
+
+-- wrapper around update(). This calls update() and if update faults
+-- then an error is displayed, but the script is not stopped
+function protected_wrapper()
+    local success, err = pcall(update)
+    if not success then
+        gcs:send_text(MAV_SEVERITY_ERROR, "Internal Error: " .. err)
+        -- when we fault we run the update function again after 1s, slowing it
+        -- down a bit so we don't flood the console with errors
+        return protected_wrapper, 1000
+    end
+    return protected_wrapper, math.floor(1000 / RATE_HZ)
+end
+
+-- start running update loop
+return protected_wrapper()