SPRUHZ7K August 2015 – April 2024 AM5706 , AM5708 , AM5716 , AM5718 , AM5718-HIREL
So that 16-bit processors can access the mailbox module, the module allows 16-bit register read and write access, with restrictions for the MAILBOX_MESSAGE_m registers. The 16-bit half-words are organized in little endian fashion; that is, the least-significant 16 bits are at the low address and the most-significant 16 bits are at the high address (low address + 0x02).
All mailbox module registers can be read or written to directly using individual 16-bit accesses with no restriction on interleaving, except the MAILBOX_MESSAGE_m registers, which must always be accessed by either single 32-bit accesses or two consecutive 16-bit accesses.
When using 16-bit accesses to the MAILBOX_MESSAGE_m registers, the order of access must be the least-significant half-word first (low address) and the most-significant half-word last (high address). This requirement is because of the update operation by the message FIFO of the MAILBOX_MSGSTATUS_m registers. The update of the FIFO queue contents and the associated status registers and possible interrupt generation occurs only when the most-significant 16 bits of a MAILBOX_MESSAGE_m are accessed.