Onboard system, communication method, and non-transitory storage medium

A communication method for an onboard system including a first ECU and a second ECU respectively installed at a vehicle and configured to communicate with each other via a transmission path using session information,

• the first ECU including:
• a first volatile memory,
• a first non-volatile memory that is not electronically data-rewritable,
• a second non-volatile memory that is electronically data-rewritable, and
• a first processor coupled to the first non-volatile memory,
• the second ECU including:
• a second volatile memory,
• a third non-volatile memory that is not electronically data-rewritable,
• a fourth non-volatile memory that is electronically data-rewritable, and
• a second processor coupled to the third non-volatile memory,
• the communication method being performed by the first processor and the second processor, the communication method comprising:
• detecting a precursor to a communication anomaly;
• in a case in which the communication anomaly precursor has not been detected, causing first session information to be stored in the first volatile memory and the second volatile memory, while not causing the first session information to be stored in the second non-volatile memory or the fourth non-volatile memory;
• and
• in a case in which the communication anomaly precursor has been detected, causing the first session information to be stored in at least the second non-volatile memory and the fourth non-volatile memory, or causing second session information that is generated by the first processor or the second processor and that is different from the first session information to be stored in at least the second non-volatile memory and the fourth non-volatile memory.

A non-transitory storage medium storing a program for a vehicle system including a first ECU and a second ECU respectively installed at a vehicle and configured to communicate with each other via a transmission path using session information,

• the first ECU including:
• a first volatile memory,
• a first non-volatile memory that is not electronically data-rewritable,
• a second non-volatile memory that is electronically data-rewritable, and
• a first processor coupled to the first non-volatile memory,
• the second ECU including:
• a second volatile memory,
• a third non-volatile memory that is not electronically data-rewritable,
• a fourth non-volatile memory that is electronically data-rewritable, and
• a second processor coupled to the third non-volatile memory,
• the program being executable by the first processor and the second processor to execute communication processing, the communication processing comprising:
• detecting a precursor to a communication anomaly;
• in a case in which the communication anomaly precursor has not been detected, causing first session information to be stored in the first volatile memory and the second volatile memory, while not causing the first session information to be stored in the second non-volatile memory or the fourth non-volatile memory;
• and
• in a case in which the communication anomaly precursor has been detected, causing the first session information to be stored in at least the second non-volatile memory and the fourth non-volatile memory, or causing second session information that is generated by the first processor or the second processor and that is different from the first session information to be stored in at least the second non-volatile memory and the fourth non-volatile memory.