Valkyrie Knowledge Base

Advanced PHY Features Port Properties

This section only applies to CFP4 and QSFP28/QSFP+ ports on 40/100G modules supporting these port types. For these ports, an additional sub-tab will appear in the main Resource Properties tab as shown in the image below (available on R.57.3 or newer).

The Advanced PHY Features include the ability to control and monitor the four receive SerDes associated with the 4x10G or 4x25G link at the physical level. This includes the possibility to read out bit-error-rate (BER) eye diagrams, estimate the link BER from the vertical and horizontal BER bathtub curves and to control the PHY tuning in the transmit and the receive directions.

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Configuration and Controls

The configuration and controls for the advanced PHY features are shown in the image below. They consist of three main sections: Diagram Control, Per SerDes TX PHY Tuning and Overall RX PHY Tuning.

controls.png


Diagram Control

This section controls the collection of the BER eye diagram and eye data as well as the parameters associated with this measurement.

Property Explanation
Collection state Shows the current state of the eye diagram measurement.
Start/Stop Collection Start/Stop eye diagram measurement.
Refresh Data Re-read current eye diagram and eye data measurement from the chassis. Press this to view the current eye measurement for the SerDes if one already exists.
X Resolution Resolution of the time-axis (horizontal). Calculated from “X Exponent” as 2^(exp) + 1. Min/Max = 9 / 65.
Y Resolution Resolution of the voltage axis (vertical). Calculated from “Y Exponent” as 2^(exp) – 1. Min/Max = 7 / 255.
X Exponent User-settable X resolution exponent. See “X-Resolution” for details). Min/Max = 3 / 6.
Y Exponent User-settable Y resolution exponent. See “Y-Resolution” for details). Min/Max = 3 / 8.
SerDes Index The SerDes for which the settings and controls listed above, as well as the Per SerDes TX PHY Tuning listed below applies. Valid values = 0..3.

Note that higher values of X and Y will give you a higher precision in the vertical and horizontal bathtub curve estimations, respectively. However, the time it takes to measure the eye is directly proportional to the number of sampling points (X*Y).


Per SerDes TX PHY Tuning 

This section allows the user to manually control and monitor the equalizer settings of the four individual 25G/10G SerDes of the on-board PHY in the transmission direction (towards the transceiver cage). The affected SerDes is selected using the “SerDes Index” parameter described under “Diagram Control”. This feature can, for example, be used to improve the signal quality over a directly attached copper cable (e.g. CR4) in the absence of automatic TX tuning auto-negotiation or to test a transceiver using various TX equalization settings.

Property Explanation
TX Pre-emphasis Transmit pre-emphasis. Values = -7..15. Default = 0 (neutral).
TX Attenuation Transmit attenuation. Values = 0..31. Default = 0 (full power).
TX Post-emphasis Transmit post-emphasis. Values = -31..31. Default = 0 (neutral).

Note: The absolute values of the three equalizer parameters (pre, attn and post) must be <= 32. So {-7 10 15} is OK, but {-8 10 15} is invalid and will be rejected by the server.


Overall RX PHY Tuning 

This section allows the user to control the tuning of the on-board PHY in the receive direction (signals coming from the transceiver): The user can enable or disable the automatic receive PHY retuning, which is performed on the 25G interfaces as soon as a signal is detected by the transceiver. This is useful if a bad signal causes the PHY to continuously retune or if for some other reason it is preferable to use manual retuning. Regardless of whether the automatic tuning is enabled, the user may also trigger a manual retuning of the PHY. Note that as opposed to the TX tuning, receive tuning affects ALL four SerDes.

Property Explanation
Auto-Tune PHY Enabled Enable/Disable the automatic RX PHY tuning upon signal detection at the transceiver.
Retune PHY Now Press to trigger a manual RX PHY tuning.


Eye Diagram

The bit-error-rate (BER) eye-diagram allows the user to get a direct visual representation of the signal quality. The eye-diagram is formed by changing the sampling point of the PHY step by step in the time dimension (sampling delay) and the amplitude dimension (0/1 threshold). For each sampling point (x,y), 1 million bits are measured and the number of bit-errors is counted. A simple division gives the BER. The result is the BER eye-diagram shown below:

eye-diagram2.png

The color map shows the measured bit-error-rate for each point going from 1 million (maximum red) to zero (black). The color scale is logarithmic. Higher resolutions give a more clear diagram and higher values of X and Y will also give a higher precision in the vertical and horizontal bathtub curve estimations, respectively (see Eye Data below). However, the time it takes to measure the eye is directly proportional to the number of sampling points (X*Y).


Eye Data

The eye-data table provides an estimate of several parameters of the eye, including width, height, and jitter. Future releases will also include link BER estimates based on the horizontal and vertical bathtub curves.

Eye Data.png
Name Description
Common Parameters
Width Estimated eye-width in mUI
Height Estimated eye-height in mV
Horizontal Bathtub Parameters
HSlope left Left slope of the horizontal bathtub curve
HSlope right Right slope of the horizontal bathtub curve
Y-intercept left Intersection with the Y-axis on the left side
Y-intercept right Intersection with the Y-axis on the right side
R-squared fit left Quality assessment of the estimation. Max = 100.
R-squared fit right Quality assessment of the estimation. Max = 100.
Est RJrms left Estimated random jitter (rms) – left side
Est RJrms right Estimated random jitter (rms) – right side
Est DJpp Estimated deterministic jitter
Vertical Bathtub Parameters
VSlope bottom Bottom slope of the vertical bathtub curve
VSlope top Top slope of the vertical bathtub curve
X-intercept bottom Intersection with the bottom X-axis
X-intercept top Intersection with the top X-axis
R-squared fit bottom Quality assessment of the estimation. Max = 100.
R-squared fit top Quality assessment of the estimation. Max = 100.
Est RJrms bottom Estimated random jitter (rms) – bottom
Est RJrms top Estimated random jitter (rms) – top

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