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 development units.)
The register dump/fatal error info can also be written to nandrw/sys/native.log. On retail consoles, the system does not notify ErrDisp that any user-land exceptions occurred, ErrDisp is only notified for this on dev/debug units. Therefore, on retail consoles native.log only contains info from fatal errors. Starting with 5.0.0-11 ErrDisp no longer writes logs to native.log, except when the error-type is value 5 and when other checks with the errorinfo structure are successful (normally processes using this port never use error-type 5).
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 handles "returning" to Home Menu via NSS:RebootSystem, which triggers a hardware system reboot.
ErrDisp error port "err:f"
|0x00020042||(size, (size<<14) | 2, errorinfoptr) This is similar to cmd1, except with this the input buffer is copied to final output errorinfo+0x80 instead of +0x0, via the ARM11 kernel. Max size is 0x100. ErrDisp doesn't do anything in the cmd-handler for this command at all, besides checking the command header and buffer header.|
Note: the following data is still only partly reliable
|2 bytes||The type of error info struct (??)|
|4 bytes||The return code of the errored function (?? - Inconsistent)|
|4 bytes||caller_ptr||The contents of the LR register - where the error was called from|
|4 bytes||process_id||The ID/Handle of the running process|