# $USINF Information Message Note: Except for the $USINF messages listed below, Cerulean Sonar may arbitrarily change the format and content of any $USINF messages at any time. Example: $USINF,Cerulean Sonar RTH ROV Locator\*6B Format: $USINF,\\*hh \ is free-form text that does not include any asterisks or newlines All $USINF messages can be safely ignored. However, several information messages can assist with calibrating and other tasks: * **$USINF,IMU status unknown** is sent at power-up. This is useful in case, for example, to indicate that power was interrupted to the receiver and it has re-booted. IMU-based data such as true bearing to the transmitter are suspect until the IMU has reported full sync. * **$USINF,IMU status All OK** is sent each time the IMU reports all sensors have achieved calibration. Note that the IM U can achieve full calibration and then drop down to a lower calibration status as anomalies are detected. Generally, once the IMU reports all OK the IMU outputs and data dependent on the IMU are good enough to use even if the IMU drops to a lower calibration status. * **$USINF,IMU Cal voided** is sent to confirm you asked to replace the IMU calibration in flash memory * **$USINF,IMU Cal written to NV RAM** is sent when a valid calibration data set has been written to flash memory * **$USINF,IMU CAL abcd** reports the calibration status of the IMU Kalman filter calibration inputs and outputs. {a,b,c,d} have values from 0 to 3, with 3 being fully calibrated, 0 being suspect. ‘a’ is system total calibration status, ‘b’ is gyroscope status, ‘c’ is accelerometer status, ‘d’ is magnetometers status ***(this message form is deprecated; use the IMU s field in the $USRTH message instead)*** * **$USINF,Starting crystal calibration** is sent to confirm the 30-minute crystal clock calibration routine has started * **$USINF,Ending crystal calibration** is sent when the 30-minute crystal clock calibration routine has ended and the clock calibration has been written to flash memory --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.ceruleansonar.com/c/rov-locator/communicating-with-the-rovl/messages-from-rovl-to-host/usdusinf-information-message.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.