SECTION 3
PCI 9080
FUNCTIONAL DESCRIPTION
PLX Technology, Inc., 1997
Page 42
Version 1.02
in the Outbound Free List FIFO. If Outbound Free List
FIFO is not empty (head and tail pointers are not equal),
the IOP can obtain the MFA of the oldest free outbound
message frame by reading the location pointed to by the
Queue Base Register + (3 * FIFO Size) + Outbound
Free Tail Pointer Register. After the IOP reads the MFA,
it must increment the Outbound Free Tail Pointer
Register. To prevent overflow conditions, I
2
O specifies
that the number of message frames allocated should be
less than or equal to the number of entries in a FIFO.
MU also checks for overflows of the Outbound Free List
FIFO. When the head pointer is incremented and
becomes equal to the tail pointer, the Outbound Free
List FIFO is full, and the MU generates a local LSERR
(NMI) interrupt. The interrupt is recorded in the Queue
Status Control (QSR) Register.
From the time that the PCI write transaction is received
until the data is written into local memory and the
Outbound Free Head Pointer Register is incremented,
any PCI direct slave access to the PCI 9080 is issued a
RETRY.
Table 3-8. Circular FIFO Summary
FIFO
Name
PCI
Port
Generate PCI
Interrupt
Generate Local
Interrupt
Head Pointer
Maintained by
Tail Pointer
Maintained by
Inbound Free
List FIFO
Inbound Queue
Port (Host read)
No
No
Local
processor
MU hardware
Inbound Post
List FIFO
Inbound Queue
Port (Host write)
No
Yes, when Port
is written
MU hardware
Local
processor
Outbound Post
List FIFO
Outbound Queue
Port (Host read)
Yes, when FIFO
is not empty
No
Local
processor
MU hardware
Outbound Free
List FIFO
Outbound Queue
Port (Host write)
No
Yes, (LSERR) when
FIFO full
MU hardware
Local
processor
3.13.10 I
2
0 Enable Sequence
To enable I
2
O, the local processor should perform the
following:
Initialize Space 1 address and range
Initialize all FIFOs and message frame memory
Set the PCI class code in Register (PCI:09h-0Bh) to
be an I
2
O device with programming interface 01h
Set the I
2
O enable bit
Set the Local Init Done bit
Note:
NB# must be pulled up so the PCI 9080 issues
retries to all PCI accesses until the Local Init Done bit is
set in register (LOC:ECh) (refer to Table 4-59) by the
local processor.
The I
2
O enable bit in the Queue Status Register (LOC:
168h; Table 4-89) causes remapping of resources for
use in I
2
O mode. When this bit is set, all memory
mapped configuration registers (such as queue ports
40h and 44h) and Space 1 share PCIBAR0 (PCI:10h,
LOC:10h; Table 4-19). PCI accesses to offset 00h-FFh
of PCIBAR0 will result in accesses to the internal
configuration registers of the PCI 9080. Accesses above
offset FFh of PCIBAR0 will result in local space
accesses beginning at offset 100h from the Local
Space 1 Remap Register (LAS1BA, LOC:174h; Table 4-
46). Therefore space located at offset 00h-FFh from
LAS1BA is not addressable by way of PCIBAR0.
Programmer’s Note:
00h-FFh of PCIBAR0 result in internal configuration
accesses, Inbound Free MFAs must be greater than
FFh.
Because PCI accesses to offset