MacOS Ventura Does Not Play Well With Raspberry Pi Pico

A problem has arisen in the way the latest version of MacOS mounts Raspberry Pi Pico virtual volumes, meaning Macs updated to 13.0 Ventura, released October 24, cannot copy across the UF2 files used for flashing instructions onto the microcontroller. The Raspberry Pi blog has a post about the error, and the company has reported it to Apple as a bug.

The Finder still mounts the volume onto the desktop when the Pico is connected over USB while the Bootsel button is held down to put it into mass storage mode, just like it would with any other volume from a flash drive to a network server, but throws an unexpected error code 100093 -  kPOSIXErrorENOATTR ("Attribute not found") - when you try to copy a file to the Pico. It seems to have something to do with the volume’s extended attributes, but whatever it means, the file does not copy across. The problem also appears to affect other boards that use "fake" virtual volumes, including third party RP2040-based boards, and there's a long discussion about the issue on GitHub.

This has led to speculation that, since Picos mounted properly in previous versions of the OS, Apple has changed something in the way Ventura deals with external volume attributes, and the Pico falls foul of the change. “We’re not entirely sure what the exact change is; possibly Finder is now carrying out an additional re-read of the metadata after write, or it could be that there has been a change in the way errors are handled based on reading incorrect data. There may even have been some sort of change to the default caching behavior,” writes Raspberry Pi’s head of documentation Alisdair Allen on the blog, also noting that it could be a combination of several changes.

There are currently two workarounds for the problem, both of which address the issue by bypassing Finder. One is to use the command line, from where you can successfully copy a UF2 file across despite yet another error message appearing, and the other is to use Raspberry Pi’s own Picotool, which can achieve the same thing. An Apple Shortcut written by Allen can also be downloaded to help matters.

Raspberry Pi is in talks with Apple about the issue, but notes that the error still occurs in the beta version of Ventura 13.1. Pico owners who encounter the issue can  send a bug report to Apple through the Feedback Assistant app on their Macs, quoting feedback number FB11725030.