2. PCI Interface
67
PowerSpan II User Manual
80A1010_MA001_09
Integrated Device Technology
www.idt.com
Figure 10: PowerSpan II I
2
O Message Passing
The Top and Bottom pointers manage external FIFOs to determine the full and/or empty status of the
FIFOs. After a FIFO write, the Top pointer is incremented. If the Top pointer then equals the Bottom
pointer, a FIFO full condition exists. After a FIFO read, the Bottom pointer is incremented. If the
Bottom pointer then equals the Top pointer, a FIFO empty condition exists.
PCI
Bus
Inbound Queue
(0x040)
Inbound
Free List
FIFO
Inbound
post List
FIFO
Outbound
Free List
FIFO
Outbound
Post List
FIFO
Bottom Pointer
Top Pointer
Bottom Pointer
Top Pointer
Top Pointer
Bottom Pointer
Top Pointer
Bottom Pointer
Local
Processor (IOP)
Inbound Queue
Outbound Queue
Outbound Queue
(0x044)
Local
Processor (IOP)