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
224
Section 8: PCI Bus and HyperTransport Fabric
Document
1250_1125-UM100CB-R
H
YPER
T
RANSPORT
D
IFFERENCES
FROM
R
EVISION
1.03 S
PECIFICATION
This section compares the HyperTransport interface with the HyperTransport I/O Link Protocol Specification
Rev 1.03 10/10/2001. This is the first specification released by the HyperTransport Consortium, the
specification details and section numbers match the 1.02 release made by AMD. Comments are made by
section number in the specification. (The sections were reordered in HT 1.04.)
1.1 Terminology
Care is needed with the term Doubleword. In HyperTransport/PCI it is used for four bytes, in
MIPS it is used for eight bytes.
2 Signaling
The interface only supports 8 bit links (8 CAD pairs, 1 CLK pair, 1 CTL pair). The optional power
management signals are not supported.
3.2.1.4 Command Encoding
The interface uses the Isochronous bit in Wr(sized) and Rd(sized) inbound (dma) commands
to set the ZBbus L2CA flag to request the access be allocated in the L2 cache on a miss. All
memory accesses will be marked cacheable coherent and all others uncached regardless of
the coherence bit in the command.
4.1 Topology
The part is always a host. If the interface revision is 3 or greater the ActAsSlave mode is
supported for double-hosted chains.
4.1.1 Double-Hosted Chains
The interface supports double-hosted chains. Designation of the master and slave end must
be done by software. The Host Hide function is not implemented. The ActAsSlave is
implemented in interface RevId 3 and greater, but is not available on earlier versions. Care is
therefore needed to understand the dataflows in sharing double-hosted chains.
In a chain with two hosts A and B, if the MAC or Serial port DMA engine on A is doing writes to
any device through the HyperTransport then accesses from B to any of the peripherals behind
I/O bridge 1 on A can cause deadlock.
4.1.2.2 Host Implementations
The interface has LDT_PWROK and LDT_RESET_L separated from the system reset. A
system reset will always cause the HyperTransport to reset until released by software. See
Section: “HyperTransport Resets” on page 260
4.2 Transactions and UnitID
The interface is a host and therefore always uses UnitID 0. In interface RevId 3 and greater the
ActAsSlave function allows the interface to use the UnitID set in the DevNum field on a double-
hosted chain.
4.4.1 Sized Writes
In byte writes nonzero byte masks are ignored for doublewords that are not sent.