This library has been deprecated and is no longer required to access QSPI flash as filesystem, check https://github.com/adafruit/Adafruit_SPIFlash for full QSPI/SPI support with SdFat as the FAT filesystem manager, its great!
This is a library for interfacing with the QSPI peripheral and external flasheds on SAMD51 and nRF52 microcontrollers.
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Written by Dean Miller and Ha Thach for Adafruit Industries. MIT license, all text above must be included in any redistribution