cx_built_in_test: debounce audible warning for nil

We recently had a case where either rpm or servo out returned nil for a
single loop for reasons that don't seem to be related to a telemetry
dropout. To narrow down the cause, we have split the nil checks in two
separate warnings. To prevent unnecessary concern, we are reducing the
severity of the warning until one of these returns nil three loops in a
row.

Also fixed an issue where continuous nil returns would result in message
spam.

SW-219

libraries/AP_HAL_ChibiOS/hwdef/CarbonixCubeOrange/scripts/cx_built_in_test.lua

@@ -118,6 +118,13 @@ local function esc_is_stopped(i)
     esc_warmup_end_time[i] = nil
 end
 
+-- Counters to debounce nil checks on esc rpm and servo output, this is a
+-- workaround to avoid giving the pilot a critical warning for an unexplained
+-- one-loop dropout we saw recently
+local NIL_WARN_THRESHOLD = 3
+local esc_rpm_nil_counter = {0, 0, 0, 0, 0}
+local servo_out_nil_counter = {0, 0, 0, 0, 0}
+
 local function esc_check_loop()
     for i = 1, number_of_esc  do
         local esc_last_telem_data_ms = esc_telem:get_last_telem_data_ms(i-1):toint()
@@ -135,6 +142,28 @@ local function esc_check_loop()
             if arming:is_armed() then
                 local esc_rpm = esc_telem:get_rpm(i-1)
                 local servo_out = SRV_Channels:get_output_pwm(srv_number[i][2])
+                if not esc_rpm then
+                    esc_rpm_nil_counter[i] = esc_rpm_nil_counter[i] + 1
+                    if esc_rpm_nil_counter[i] < NIL_WARN_THRESHOLD then
+                        gcs_msg(MAV_SEVERITY_INFO, "ESC " .. i .. " RPM nil")
+                    elseif srv_rpm_in_err_status[i] == false then
+                        gcs_msg(MAV_SEVERITY_CRITICAL, "ESC " .. i .. " RPM nil")
+                        srv_telem_in_err_status[i] = true
+                    end
+                else
+                    esc_rpm_nil_counter[i] = 0
+                end
+                if not servo_out then
+                    servo_out_nil_counter[i] = servo_out_nil_counter[i] + 1
+                    if servo_out_nil_counter[i] < NIL_WARN_THRESHOLD then
+                        gcs_msg(MAV_SEVERITY_INFO, "ESC " .. i .. " Servo Out nil")
+                    elseif srv_rpm_in_err_status[i] == false then
+                        gcs_msg(MAV_SEVERITY_CRITICAL, "ESC " .. i .. " Servo Out nil")
+                        srv_telem_in_err_status[i] = true
+                    end
+                else
+                    servo_out_nil_counter[i] = 0
+                end
                 if esc_rpm and servo_out then
                     -- If the PWM is below the threshold, consider it a stopped motor situation
                     if servo_out < SERVO_OUT_THRESHOLD then
@@ -156,9 +185,6 @@ local function esc_check_loop()
                             end
                         end
                     end
-                else
-                    gcs_msg(MAV_SEVERITY_CRITICAL, "ESC " .. i .. " Null Rcout or RPM")
-                    srv_telem_in_err_status[i] = true
                 end
             end
         end