AP_Scripting: add callback time test script

libraries/AP_Scripting/tests/callback_time_test.lua

@@ -0,0 +1,37 @@
+-- Test call back times from 2^0 to 2^18 (0.001 to 262.144 seconds)
+local power = 0
+local end_power = 18
+
+-- The error must be less than the larger of the two thresholds
+-- This can be (alot) smaller if speedup is not used
+local absTheshold = 250
+local pctThreshold = 1
+
+local last_run_us
+
+local function update()
+  local now_us = micros()
+
+  local expectedDelay = (2^power) / 1000
+  local measuredDelay = (now_us - last_run_us):tofloat() / 1000000
+  local error_ms = (expectedDelay - measuredDelay) * 1000
+
+  print(string.format("Timing test want: %0.3f s, got: %0.3f s, error: %0.3f ms", expectedDelay, measuredDelay, error_ms))
+
+  local threshold = math.max(absTheshold, expectedDelay * 10 * pctThreshold)
+  if math.abs(error_ms) > threshold then
+    error(string.format("Large timeing error! (>%0.3fms)", threshold))
+  end
+
+  power = power + 1
+  if power > end_power then
+    print("Timing test passed")
+    return
+  end
+
+  last_run_us = micros()
+  return update, 2^power
+end
+
+last_run_us = micros()
+return update, 2^power