BCM1250/BCM1125/BCM1125H
User Manual
10/21/02
B r o a d c o m C o r p o r a t i o n
Page
226
Section 8: PCI Bus and HyperTransport Fabric
Document
1250_1125-UM100CB-R
6.1 Upstream I/O Ordering
The interface follows the ordering rules through the HyperTransport Interface into the I/O
Bridge.
6.2 Host Ordering Rules
The ordering rules are maintained into the ZBbus domain, which has a different set of rules.
The same ordering is used for Cacheable and Non-Cacheable commands, and the rules for
these, interrupt messages and responses are maintained correctly. However, because the
ZBbus allows responses to pass posted writes care must be taken when using the producer-
consumer model as described in point 10 of the previous section.
6.2.1 Host Responses to Nonposted Requests
A non-posted write is acknowledged as the transaction leaves the HyperTransport interface
and becomes a posted write internally. See point 13 of the previous section.
6.4 Ordering in Sharing Double-Hosted Chains
The I/O Bridge and HyperTransport interface will always push posted writes ahead of read
responses. But this is not the case internally and care must be taken because the ZBbus
always allows read responses to pass posted writes. See the
.
7.1 Configuration Cycle Types
Configuration Cycles are generated as described in
Section: “Configuration of PCI and
7.3.1.1 I/O Space Enable, 7.3.1.2 Memory Space Enable
These bits are always set because the address decoders on the ZBbus are always active.
7.3.8 Interrupt Line
The Interrupt Line register is not writeable.
7.3.2.3, 7.3.2.4, 7.3.2.5 Primary Bus Error Status bits
These bits are always clear because errors on the ZBbus side are reported in other ways.
7.4.8.3 ISA Enable
The optional ISA address scrambling is not supported so this bit is always 0.
7.4.8.4 VGA Enable
The optional VGA address forwarding is supported so this bit is R/W. The implementation is
described in
Section: “The SouthBridge, VGA and Subtractive Decode” on page 195
.
7.5 Capability Registers
The interface uses the Host Format from the earlier HyperTransport specifications, these cover
the +00, +04 and +08 offsets of the block in Table 29 of the HyperTransport specification.
Interface revision 3 uses the format from the 1.03 specification.