Critical Issue
Description
The altera_avalon_mailbox peripheral might not
be initialized properly when a soft (non-system-wide) reset occurs.
In this condition, mailbox contents (read and write pointers) are
not reinitialized and might show potentially stale data.
Resolution
Ensure that a system-wide reset event occurs by asserting
the reset_n input to the SOPC Builder system containing
the mailbox. This resets all peripherals and Nios II processors
in the system.