I would like to store an application's configuration in a file stored on the Circuit Playground Express (CPX) flash. The application itself needs to be able to update the configuration file. Things I need to store are basic, for example:

  • NeoPixel brightness (eg. brightness = 0.9)
  • NeoPixels on/off (eg. NP_enable = [0,0,1,0,1,0,1,1,1,1]

ArduinoJason seems appropriate, but I cannot even get to the point of writing files to the CPX. The TinyUSB libraries are supposed to give the ability to write to the CPX SPI Flash, but I cannot get any of the examples included with this library to compile. I am trying to compile the msc_external_flash example provided with the TinyUSB library. I get the following 2 errors:

In file included from /home/pi/Arduino/libraries/Adafruit_TinyUSB_Library/examples/MassStorage/msc_external_flash/msc_external_flash.ino:28:0:
/home/pi/Arduino/libraries/Adafruit_TinyUSB_Library/src/Adafruit_TinyUSB.h:31:2: error: #error TinyUSB is not selected, please select it in "Tools->Menu->USB Stack"
#error TinyUSB is not selected, please select it in "Tools->Menu->USB Stack"
msc_external_flash:65:6: error: #error No QSPI/SPI flash are defined on your board variant.h !
#error No QSPI/SPI flash are defined on your board variant.h !

The board selected is SAMD-->Circuit Playground Express. There is no Tools menu item for selecting the USB stack.

Regarding the second error, From msc_external_flash.ino:

    Adafruit_FlashTransport_QSPI flashTransport;
  #elif defined(EXTERNAL_FLASH_USE_SPI)
    Adafruit_FlashTransport_SPI flashTransport(EXTERNAL_FLASH_USE_CS, EXTERNAL_FLASH_USE_SPI);
    #error No QSPI/SPI flash are defined on your board variant.h !

of the files named variant.h, this looks like the best candidate: /home/pi/.arduino15/packages/arduino/hardware/samd/1.8.12/variants/circuitplay/variant.h

but the file does not contain the string "EXTERNAL_FLASH", nor anything I see that is CPX specific.

Arduino version is 1.8.19, which I am running on a Raspberry Pi 3 B+ running Buster.

Thanks, Scott

  • please describe the problem and ask a question ... this site is not a forum
    – jsotola
    Feb 23, 2022 at 0:20
  • ArduinoJson has an example that reads a configuration file from the SD card. See JsonConfigFile.ino. You can easily adapt it for any other filesystem, such as SPIFFS and LittleFS. Feb 23, 2022 at 7:27
  • install the Adafruit SAMD core. it looks like you are using the Arduino SAMD core, which has only basic support for the Adaruit board
    – Juraj
    Mar 5, 2022 at 6:13
  • The board selected is SAMD-->Circuit Playground Express. I can run other CPX examples, like IRNeoPixels, I assume I have the Adafruit SAMD core. Mar 7, 2022 at 15:42
  • yes but you can't compile Adafruit specialties with the Arduino SAMD core
    – Juraj
    Mar 8, 2022 at 5:30

1 Answer 1


The problem was using the Arduino SAMD board core instead of the Adafruit SAMD board core. The Adafruit SAMD board core is not visible unless you add: https://adafruit.github.io/arduino-board-index/package_adafruit_index.json

to the "Additional Boards Manager URLs:" field of the Arduino IDE preferences panel.

Once you do that... Then install the "Adafruit SAMD Boards" from the Arduino IDE Boards Manager. Then select the menu item: Tools --> Board: --> Adafruit SAMD (32-bits ARM Cortext-M0+ and Cortext-M4) boards --> Adafruit Circuit Playground Express (SAMD21)

I have not seen this procedure in any Adafruit documentation.


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