8–4
Chapter 8: Reset and Clocks
Clocks
Arria V GZ Hard IP for PCI Express
November 2012
Altera Corporation
As
illustrates, the RX transceiver reset includes the following steps:
1. After
rx_pll_locked
is asserted, the LTSSM state machine transitions from the
Detect.Quiet to the Detect.Active state.
2. When the
pipe_phystatus
pulse is asserted and
pipe_rxstatus[2:0]
= 3, the
receiver detect operation has completed.
3. The LTSSM state machine transitions from the Detect.Active state to the
Polling.Active state.
4. The Hard IP for PCI Express asserts
rx_digitalreset
. The
rx_digitalreset
signal
is deasserted after
rx_signaldetect
is stable for a minimum of 3 ms.
illustrates the TX transceiver reset sequence.
As
illustrates, the RX transceiver reset includes the following steps:
1. After
npor
is deasserted, the core deasserts the
npor_serdes
input to the TX
transceiver.
2. The SERDES reset controller waits for
pll_locked
to be stable for a minimum of
127 cycles before deasserting
tx_digitalreset.
Clocks
The Hard IP contains a clock domain crossing (CDC) synchronizer at the interface
between the PHY/MAC and the DLL layers which allows the Data Link and
Transaction Layers to run at frequencies independent of the PHY/MAC and provides
more flexibility for the user clock interface. Depending on parameters you specify, the
core selects the appropriate
coreclkout_hip
as listed in
Table 8–1 on page 8–1
. You
can use these parameters to enhance performance by running at a higher frequency
for latency optimization or at a lower frequency to save power.
In accordance with the
PCI Express Base Specification 2.1
, you must provide a 100 MHz
reference clock that is connected directly to the transceiver. As a convenience, you
may also use a 125 MHz input reference clock as input to the TX PLL.
Figure 8–4. TX Transceiver Reset Sequence
npor
pll_locked
npor_serdes
127 cycles
tx_digitalreset