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The NTSB’s report explains how Tesla stores its captured data.

The report noted, “As part of Forward Collision Warning (FCW) and Automatic Emergency Braking (AEB) event data, the vehicle supports the acquisition and storage of image data captured by the forward facing camera. This system can buffer 8 frames of image data sampled at one second intervals centred upon a triggering FCW/AEB event. These frames are initially captured in volatile memory in the Camera ECU and then stored in non-volatile memory at the end of the drive. From there it is transferred via CAN bus to the Gateway ECU where it is stored on the internal SD card.” Then, “data from the SD card is episodically data-linked to Tesla servers,” the report says.

Although the data flow described in the report might be a revelation to some, it goes no further about the types of memory used.

VSI, which did a deep dive into Tesla’s Model S a few months ago, shared a few more details and educated guesses.

According to VSI’s Kim, Nvidia’s Tegra SoC, which is part of the MCU motherboard, features volatile memory SK Hynix DDR3 SDRAM (4Gbytes–there are four 4GB slots) and 8GB flash memory. "Along with the Nvidia PCB, the MCU motherboard also contains connectivity modules, microcontroller, FPGA, Ethernet Switch and the 4GB SD memory (for EDR)," he explained.

Kim said VSI believes that inside the vehicle all data is recorded in real-time. VSI speculates that real-time recording would be writing to the 8GB onboard flash drive (not the removable SD card) on the Nvidia Tegra SOC because it has the fastest write speed. Once data is saved on the 8GB flash memory, perhaps after extra processing, VSI suspects that “some of that data is copied to the SD card for long term storage and to be more easily accessed.”

VSI also believes that “perhaps not all of the raw data is copied to the SD card, but perhaps only certain data points the system deems important.” For example, such data could be certain key time interval, or certain data elements like timestamps, vehicle speed data, Auto Pilot engagement and actuation data (steering angle, brakes). Excluded would be larger sensor data (camera frames and radar). This would allow a Tesla engineer to be able to quickly see the most important information and a summary of events, and if necessary, know where to look for more raw data.

NTSB_tesla-crash_02 (cr) Figure 1: 2D diagram of collision area based on 3D scan and Florida Highway Patrol Data (Source: NTSB)

What recovered data did not show

While industry analysts were most curious about what exactly Tesla’s recovered data revealed about the crash, they were disappointed that the NTSB report was not able to find what the camera saw.

NTSB_tesla-crash_03 (cr) Figure 2: Crash scene intersection, looking east (Source: NTSB)

The report said, “Image data from the vehicle’s camera was recovered from the SD card. By design, this data does not contain any timestamp information. The recovered image data did not contain information consistent with the crash.” The report speculates that “these images were likely triggered by an earlier FCW/AEB event and written to the SD card prior to the last trip.”

The Linley Group’s Demler observed, “It is very curious that they couldn’t recover any images from the Mobileye camera.”

Tesla’s OTA capabilities

Given Tesla’s ability to link up with its servers and to store data in the car that expands the information contained on the servers, VSI’s Magney was most impressed with Tesla’s Over-the-Air (OTA) capabilities. He noted, “Based on our examinations, it is my opinion that the Tesla vehicle architecture is a proxy for future vehicle platforms.” He noted, “Albeit Tesla is a maverick in this space, their OTA architecture plus event handling and data recording is vital for proper Autonomous Vehicle management.”

Magney added, “Frankly, I am little bit surprised other OEMs are nowhere near as advanced as Tesla in terms of their ability to manage their vehicle remotely. This industry has been talking about this for years but only Tesla manages their vehicles as a proper digital device.”

First published by EE Times U.S.

 
« Previously: 'Treasure trove' Tesla crash probe falls short