Altera UG-01080 Guía de usuario Pagina 171

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Chapter 8: PHY IP Core for PCI Express (PIPE) 8–19
Link Equalization for Gen3 Data Rate
November 2012 Altera Corporation Altera Transceiver PHY IP Core
User Guide
The tuning sequence typically includes the following steps:
1. The Endpoint receives the starting presets from the Phase 2 training sets sent by
the Root Port.
2. The circuitry in the Endpoint receiver determines the BER and calculates the next
set of transmitter coefficients using FS and LF and embeds this information in the
Training Sets for the Link Partner to apply to its transmitter.
The Root Port decodes these coefficients and presets, performs legality checks for
the three transmitter coefficient rules and applies the settings to its transmitter and
also sends them in the Training Sets. Three rules for transmitter coefficients are:
a. |C
-1
| <= Floor (FS/4)
b. |C-1|+C
0
+|C
+1
| = FS
c. C
0
-|C
-1
|-|C
+1
|>= LF
Where:
C
0
is the main cursor (boost)
C
-1
is the pre-cursor (pre shoot)
C
+1
is the post-cursor (de emphasis)
3. This process is repeated until the downstream component's receiver achieves a
BER of < 10
-12
.
Phase 3 (Optional)
During this phase, the Root Port tunes the Endpoint’s transmitter. This process is
analogous to Phase 2 but operates in the opposite direction.
1 If you are using the PHY IP Core for PCI Express (PIPE) PCI Express as a Root Port,
you cannot perform Phase 3 tuning.
Once Phase 3 tuning is complete, the Root Port moves to Recovery.RcvrLock, sending
EC=2’b00, along with the final coefficients or preset agreed upon in Phase 2. The
Endpoint moves to Recovery.RcvrLock using the final coefficients or preset agreed
upon in Phase 3.
Recommendations for Tuning Link Partner’s Transmitter
To improve the BER of the StratixV receiver, Altera recommends that you turn on
Adaptive Equalization (AEQ) one-time mode during Phase 2 Equalization for
Endpoints or Phase 3 Equalization for Root Ports. You enable AEQ through the
Transceiver Reconfiguration Controller IP Core. For more information about this
component, refer to Transceiver Reconfiguration Controller IP Core. For more
information about running AEQ, refer to AEQ Registers.
1 AEQ must be turned off while switching from Gen3 to Gen1 or from Gen3 to Gen2.
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