Message and error handling - MD30

MD30 Interface Description

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User guide

The mobile sensor records the time when the message handling starts. The mobile sensor expects to receive a complete message within the given time, which is known as data discarding period. If a checksum error is detected, all received data is discarded until data discarding period has passed. If message reception is not ready by the end of data discarding period, the receiver is reset and the received data bytes are ignored. The unit is ready to receive the next message after the response message sending has started or the data discarding period has passed.

Figure 1. Error handling

Response time

In case a checksum error is acknowledged, the receiver waits the data discarding period of 20 ms before producing a response message. The data discarding period is included in the total response time. Disabling the checksum error acknowledgment does not affect the total time. Incomplete messages and time-outs have the same total time, but are not acknowledged.

The mobile sensor is expected to start data handling and to produce a response message in 500 ms after data reception has started. This is the total response time, including message handling delays and the data discarding period. This time does not include the time it takes to physically transmit and receive the message at a given data rate. Ongoing continuous data sending may be interrupted for the duration of the message handling.

Response times of up to 2.5 seconds can be expected from messages that update several parameters. The SET ROAD COEFFICIENTS message has the longest response time. Ongoing continuous data sending is interrupted for the duration of the message handling. Also the SET REFERENCES message updates several parameters. The response is sent within 500 ms, but the parameter update takes place after the data collection period. During the parameter update, continuous data sending frequency cannot be guaranteed. Assigned data sending frequency is assumed as soon as the parameter update is over.

Buffer overflow

Buffer overflow occurs if the mobile sensor receives a message that does not fit into the data buffer that is allocated for data reception. In case of buffer overflow, the receiver is reset and no acknowledgment is sent.