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
255
S
YSTEM
R
ESET
I
NITIALIZATION
OF
THE
H
YPER
T
RANSPORT
I
NTERFACE
There are a number of parameters that must be configured in the HyperTransport interface before the
HyperTransport link can come out of reset and the link initialization described in the HyperTransport
Specification can start. These registers should be programmed and then the SipReady bit in the SRI Command
Register set. Once this bit is set the HyperTransport interface will come out of reset, remove the link reset, and
start the link initialization.
Most of the configuration is setting up the HyperTransport receive and transmit FIFO clocks. A high level view
of this is shown in
. Data from the fabric is loaded into the receive FIFO using the clock that was
received with the data. It is unloaded using the internal HyperTransport interface clock and passed to the
receive logic. Data from the transmit logic is loaded into the transmit FIFO using the internal HyperTransport
interface clock and extracted using the link transmit clock. The FIFOs both buffer clock speed differences and
provide time for the data to stabilize as it crosses the clock boundary.
Figure 50: HyperTransport Interface Clocks and FIFOs
÷
4
DDR
HT PLL
x(2,3,4,5,6,8,10)
Link Frequency
Register
Unload Pointer
Load Pointer
Transmit FIFO
8 x 32 Bit
Load Pointer
Unload Pointer
HT
Transmit
Logic
HT
Receive
Logic
Receive FIFO
8 x 32 Bit
HT Internal Clock (f
LDTINT
)
RX Data
RX Clock
TX Data
32
32
100 MHz Reference
8
32
32
TX Clock
(f
TX
)
(f
RX
)
I/O Clk