![Altera PHY IP Core Скачать руководство пользователя страница 145](http://html.mh-extra.com/html/altera/phy-ip-core/phy-ip-core_user-manual_2910918145.webp)
Chapter 9: Deterministic Latency PHY IP Core
9–3
March 2012
Altera Corporation
Altera Transceiver PHY IP Core
User Guide
Achieving Deterministic Latency
Figure 9–2
illustrates the TX and RX channels when configured as a wireless
basestation communicating to a remote radio head (RRH) using a CPRI or OBSAI
interface.
Figure 9–2
also provides an overview of the calculations that guarantee
deterministic delay. As this figure illustrates, you can use a general-purpose PLL to
generate the clock that drives the TX CMU PLL or an external reference clock input
pin.
In the current release, Altera recommends that you use a delay estimate FIFO to
measure the phase difference between the
tx_clkout
and
rx_clkout
, and the clock
output of the PLL to ensure the delay through the FIFO to a certain accuracy.
Systems that require multiple PLLs in a single transceiver block must use a delay
estimate FIFO to determine delay estimates and the required phase adjustments.
Delay Estimation Logic
This section provides the equations to calculate delays when the Deterministic
Latency PHY IP core implements CPRI protocol. CPRI defines the radio base station
interface between network radio equipment controllers (REC) and radio equipment
(RE) components.
Figure 9–2. Achieving Deterministic Latency for the TX and RX Datapaths
(1)
No
t
e
t
o
Figu
r
e 9–2
:
(1) The TX and RX Phase Compensation FIFOs always operate in register mode.
TX PLL refclk
or external refclk pin
TX data
RX data
bitslipboundaryselect (from RX Word Aligner)
TX PMA
tx_dataout
D
Q
D
Q
Serializer
RX PMA
De-
serializer
Bit Slip
CMU
PLL
GPLL
CDR
refclk
refclk
(from on- or
off-chip PLL)
<n>
8B/10B
rx_datain
Remote
Radio
Head
RX PCS
TX PCS
Achieving Deterministic Latency for the TX and RX Datapaths
RX Phase
Comp
FIFO
TX Phase
Comp
FIFO
tx_clkout
TX feedback (for Remote Radio Head only)
rx_clkout
Byte
Serializer
2
Byte
Deserializer
2
8B/10B
Word
Aligner