No, sorry, we don't have a Statement Of Volatility . It's on my long to-do list, as we've had several requests.
Here's the basic info, as an informal forum message. Hopefully this can at least help for now?
Teensy 4.x has a built-in flash memory wipe function, which fully erases all user programmable non-volatile memory. Press and hold the pushbutton for 13 to 17 seconds to initiate. The red LED blinks at 13 seconds to indicate pushbutton release within 4 seconds will start the memory wipe. Full erase takes about 1 minute, during which time the red LED remains on. When completed, a simple LED blink program is written to the flash memory. You will see the red LED turn off and the orange LED blinks when the process is completed. (a video demo is on my to-do list)
Teensy 4.x also has a small 256 byte fuse memory meant for permanent storage of critical settings. This memory can not be erased. Finer details of this fuse memory, its locking mechanism, and which portions are user writable on standard and lockable Teensy are the main work still needed to publish an official Statement Of Volatility. Details can be found in the chip's
reference manual, chapters 22 and 23 from pages 1287 to 1354. But to be honest, that info is highly technical and presented in a very difficult format to digest, and lacks info about how the chip is actually configured and used in practice. Something much simpler and more specific to real world usage is needed for an official Statement Of Volatility. We probably also need to add an example program to display what is stored in the fuse memory in a format that's easy to understand.
Teensy 4.1 has a SD socket. SD cards are common commodity products, not sold by PJRC. To erase the SD card, physically remove it from Teensy 4.1 and use 3rd party SD card reader/writer hardware & software to erase the SD card.
Teensy 4.1 has 2 empty locations to add memory chips, either PSRAM or Flash. PSRAM is volatile, just turn off power. For Flash memory, the LittleFS lowLevelFormat() function should be used to fully erase. We probably need to add an example program to the LittleFS library.
