The boot counter is a uint8_t single-byte counter stored in the first NVM byte position (`micrcontroller.nvm[0]`). The counter increments by 1 each time the board boots, regardless if it's a hard or soft reset.
Enable the boot counter by adding `#define CIRCUITPY_BOOT_COUNTER 1` to your board's mpconfigboard.h file. Note that an error will be thrown during the build if `CIRCUITPY_INTERNAL_NVM_SIZE` is not also set within mpconfigboard.h.
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