FeRAM for data logging
One of the key reasons for doing mass, real-time data logging in vehicles with ADAS features is to capture what happens if something goes wrong. So, developers can learn from it and stop it from happening again. For example, some ADAS implementations are not good at identifying pedestrians, especially at night. Rigorous data logging, in which all the relevant sensor data is captured, timestamped, and stored in real-time, can provide a snapshot of what was happening at the time of an incident. It can then be used to drive a process of continuous model refinement that improves the ADAS implementation.
The non-volatile ferroelectric random-access memory (FRAM) can serve this purpose. Unlike traditional non-volatile memory technologies such as flash and EEPROM, FRAMs, also known as FeRAMs, have fast write times, support instant non-volatility, are as easy to address as SRAMs and, crucially, have almost unlimited endurance, reaching 1014 read/write cycles.
Their one drawback is that they don’t have as much density as other memory types. However, in practice, this issue is mitigated by using the FRAM as a rolling buffer for ADAS data streams. If a vehicle loses power, the FRAM data log will hold a snapshot of the data available to the ADAS computers up to that point.
Moreover, there aren’t yet any mandates about how much data a vehicle should log if it has a catastrophic failure. However, SAE International is already offering guidelines about what type of data should be stored. Similar specifications are in development in Europe. But it seems likely that developers will be asked to ensure that their vehicles can capture and store 5 seconds worth of data about issues such as acceleration, braking effort and seatbelt status, as well as four images per second for 5 seconds from each of the onboard cameras.
The data-logging memory must understand what happens when vehicles have issues and provide the insights necessary to improve the ADAS features, so it doesn’t happen again. One such memory chip is MB85RC64TAPNF-G-AWERE2; it’s targeted at data logging applications in ADAS and has been qualified to the ASIL-B functional safety standard.