Freescale Semiconductor MPC8260 - Manual (Page 375)

PCI Bridge
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 9-69
9.12.3 I
2
O Unit
The Intelligent Input Output specification (I
2
O) was established in the industry to allow
architecture-independent I/O subsystems to communicate with an OS through an abstraction layer. The
specification is centered around a message passing scheme. An I
2
O embedded peripheral (IOP) is
comprised of memory, processor, and input/output device(s). An IOP dedicates space in its local memory
to hold inbound (from the remote host) and outbound (to the remote host) messages. The space is managed
as memory-mapped FIFOs, with pointers to this memory maintained in hardware.
Messages are made up of frames which are a minimum of 64-bytes in length. The message frame address
(MFA) is the address which points to the first byte of the message frame. The messages are located in
local-system memory. Tracking of the status and location of these messages is done with four FIFOs (two
FIFOs for inbound and two for outbound messages) also located in local-system memory. Hardware
registers inside the PCI bridge’s core logic manage these FIFOs. One FIFO in each queue keeps track of
the free MFAs (Free_LIST FIFO). The other FIFO keeps track of the MFAs which have posted messages
(Post_LIST FIFO).
Figure 9-64 shows an example of the message queues, although there is no specific
order that these queues must follow.
Table 9-49. IDR Field Descriptions
Bits Name Access Description
31 IMC Write 1 to set from PCI.
Write 1 to clear from local processor. Machine check. Writing to this bit will generate a machine
check interrupt to the local processor.
30–0 IDR x Write 1 to set from PCI.
Write 1 to clear from local processor. Inbound door bell x, where x is each bit. Writing a bit in this
register from the PCI bus causes an interrupt to be
generated through
t he PCI bridge to the local processor.