User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 8: PCI Bus and HyperTransport Fabric Page
231
E.3 Subtractive Decode
Subtractive Decode is discussed in the
“The SouthBridge, VGA and Subtractive
F.1 Interrupts
The interface follows the x86 interrupt mechanism as outlined in
. Interrupt messages and EOI are generated by software as described
in Section EOI Signalling Space on
Section: “HyperTransport End Of Interrupt (EOI) Signaling
.
In logical mode IntrDest[31:2] bits are ignorred and the low two bits used to select the
processor(s) that will receive the interrupt. The MT[3] bit is ignored so legacy PIC NMI and
ExtInt get mapped on to the regular NMI and ExtInt interrupts.
G. CRC Testing Mode
The CRC Testing mode is supported. The data used during the test is UNPREDICTABLE.
H. Doubleword Based Data Buffer Flow Control
The interface does not support the optional doubleword flow control.
O
RDERING
R
ULES
The HyperTransport fabric and the PCI bus have a set of ordering rules described in Appendix E of the PCI
specification revision 2.2. These differ from the more relaxed ordering rules used on the ZBbus. The PCI/
HyperTransport rules are imposed in the I/O bridge which will allow posted writes to pass reads and will not
allow read responses to pass posted writes, allowing the producer-consumer model to be used. Using this
model requires some care, see
Section: “Ordering Rules and Device Drivers” on page 14
A deadlock exists in the ordering boundary between the ZBbus and I/O Bridge 1 (in the HyperTransport terms
bridge 1 does not have sufficient virtual channels). This is only provoked when writes from I/O Bridge 1 are
targeted at the PCI/HT space (the access must have come from one of the MAC or Serial DMA engines) at the
same time as any write is in progress from the PCI/HT to any address serviced by Bridge 1 (see
for the devices that are serviced by Bridge 1) or a read is in progress from I/O Bridge 1 to
bridge 0. This deadlock can be avoided by forbidding the Bridge 0 to Bridge 1 writes and the Bridge 1 to Bridge
0 reads.