This system process handles displaying the error screens, such as "An error has occurred, the system needs shutdown". This can also display a register dump for exceptions, and info for fatal errors. (Normally the black-screen errors are displayed on retail, while the latter is displayed on dev units.)
The register dump/fatal error info can also be written to nandrw/sys/native.log, but this is normally disabled on retail as well. The retail ARM11 kernel does not notify err:f that any user-land exceptions occurred, this is likely only enabled for the dev/debug ARM11 kernel.
The bottom screen displays the error screen like "error has occurred", even with a development 3DS. The top screen can display the development error info, this is only displayed when UNITINFO bit0 is clear, for a development 3DS.
ErrDisp error port "err:f"