Revision 1.02 – April 12, 2007
S5920 – PCI Product: Mailbox Overview
Data Book
Reading the PCI Incoming Mailbox:
1. Check Mailbox Status. Read the mailbox status register to determine if any information has been passed from
the Add-On interface.
MBEF
Bits 31:28
If a bit is set, valid data is contained in the corresponding mailbox byte.
2. Read Mailbox. Read the mailbox bytes which MBEF indicates are full. This automatically resets the status bits
in the MBEF and AMBEF registers.
IMB
Bits 31:0
Mailbox data.
Writing the PCI Outgoing Mailbox:
1. Check Mailbox Status. Read the mailbox status register to determine if information previously written to the
mailbox has been read by the Add-On interface. Writes to full mailbox bytes overwrite data currently in the
mailbox (if not already read by the Add-On interface). Repeat until the byte(s) to be written are empty.
MBEF
Bits 15:12
If a bit is set, valid data is contained in the corresponding mailbox byte
and has not been read by the Add-On.
2. Write Mailbox. Write to the outgoing mailbox byte(s).
OMB Bits 31:0 Mailbox data.
Mailbox operations for the Add-On interface are functionally identical. The following sequences are suggested for
Add-On mailbox operations using status polling (interrupts disabled):
Reading an Add-On Incoming Mailbox:
1. Check Mailbox Status. Read the mailbox status register to determine if any information has been passed from
the PCI interface.
AMBEF
Bits 15:12
If a bit is set, valid data is contained in the corresponding mailbox byte.
2. Read Mailbox. Read the mailbox bytes which AMBEF indicates are full. This automatically resets the status
bits in the AMBEF and MBEF registers.
AIMB
Bits 31:0
Mailbox data.
Writing an Add-On Outgoing Mailbox:
1. Check Mailbox Status. Read the mailbox status register to determine if information previously written to the
mailbox has been read by the PCI interface. Writes to full mailbox bytes overwrite data currently in the mailbox
(if not already read by the PCI interface). Repeat until the byte(s) to be written are empty.
AMBEF
Bits 31:28
If a bit is set, valid data is contained in corresponding mailbox byte and
has not been read by the PCI bus.
2. Write Mailbox. Write to the outgoing mailbox byte(s).
AOMB Bits 31:0 Mailbox data.
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DS1596
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AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
