Nucleo F401 shows as a 33 KB mass stage device

What causes this.? I try to load software and get the infamous “no space on device” error. If I move the Nucleo to another host computer it still is seen as a 33KB mass storage device, not the 512K it should be.

No the device is not full of files, it shows as 33KB capasity

But here is an odd thing. One in about 50 attempts actually works and I can download my software. But then I need to fix a bug and it takes another 45 minutes to get the software working. So the error is not 100%, just about 98%, It actually works about 2% of the time.

If it matters this is (mostly) on MacOS.


  1. re-flashed the firmware, 5 or 6 times
  2. look for and remove any hidden files and directories (.Thrash) event doing “rm -f *”
  3. Unplug the cable and reset
  4. using different USB ports and different cables

Is the device simply broken? One would think reflashing the ST-Link firmware would either fix this or find an error with corrupted flash ROM when it tries to verify the re-flash

I searched the forums and this seems to be a recurring problem over the last few years.

What to try?

Hw to verify to the board is dead-for-good. vs. dumb-user-error I don’t want to toss out stacks of good Nucleo boards.

That issue is symptomatic of the main processor not being in a “run” state when the USB processor connects to the PC. This can happen if the external power jumper is in place instead of the USB power jumper and/or other JTAG jumpers being in the wrong position or missing.
So double-check the jumpers per the Nucleo manual and make sure the correct LEDs are illuminated when connected to the PC and report back.