Non-System-Wide Reset Can Cause Improper Initialization of Mailbox Core

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.