Revision 1.02 – April 12, 2007
S5920 – PCI Product: Mailbox Overview
Data Book
Servicing a PCI Mailbox Interrupt (INTA# asserted):
1. Identify the interrupt source(s). Multiple interrupt sources are available on the S5920. The interrupt service
routine must verify that a mailbox generated the interrupt (and not some other interrupt source).
INTCSR
INTCSR
INTCSR
Bit 23
Bit 17
Bit 16
PCI interrupt asserted
PCI incoming mailbox interrupt indicator
PCI outgoing mailbox interrupt indicator
2. Check mailbox status. The mailbox status bits indicate which mailbox bytes must be read or written.
MBEF
MBEF
Bits 31:28
Bits 15:12
Full PCI incoming mailbox bytes
Empty PCI outgoing mailbox bytes
3. Access the mailbox. Based on the contents of MBEF, mailboxes are read or written. Reading an incoming
mailbox byte clears the corresponding status bit in MBEF.
OMB
IMB
Bits 31:0
Bits 31:0
PCI outgoing mailboxes
PCI incoming mailboxes
4. Clear the interrupt source. The PCI INTA# signal is deasserted by clearing the interrupt request. The request
is cleared by writing a 1 to the appropriate bit.
INTCSR
INTCSR
Bit 17
Bit 16
Clear PCI incoming mailbox interrupt
Clear PCI outgoing mailbox interrupt
Servicing the Add-On mailbox interrupt (IRQ# asserted):
1. Identify the interrupt source(s). Multiple interrupt sources are available on the S5920. The interrupt service
routine must verify that a mailbox generated the interrupt (and not some other interrupt source).
AINT
AINT
AINT
Bit 23
Bit 17
Bit 16
Add-On interrupt asserted
Add-On outgoing mailbox interrupt indicator
Add-On incoming mailbox interrupt indicator
2. Check mailbox status. The mailbox status bits indicate which mailbox bytes must be read or written.
AMBEF
AMBEF
Bits 31:28
Bits 15:12
Empty Add-On outgoing mailbox bytes
Full Add-On incoming mailbox bytes
3. Access the mailbox. Based on the contents of AMBEF, mailboxes are read or written. Reading the incoming
mailbox byte clears the corresponding status bit in AMBEF.
AIMB
Bits 31:0
Bits 31:0
Add-On incoming mailbox
Add-On outgoing mailbox
AOMB
AMCC Confidential and Proprietary
DS1596
116
AMCC [ APPLIED MICRO CIRCUITS CORPORATION ]
