First White Rabbit Tutorial Workshop, Barcelona (Spain), 7 October 2017
With the occasion of the ICALEPCS 2017
conference, we took the opportunity to organize a special type of
workshop. Traditionally, WR
had been organized around contributions of WR users who come and show
their latest developments. They are also a great time to discuss
informally and catch up with the latest developments. This time we to
catered also for potential WR users, people who have a problem to
solve and would like to understand how WR can help them solve that
problem. We therefore decided to organize the first WR tutorial
This format is adapted to typical attendees of the ICALEPCS conference.
But we also wanted to see the usual WR workshop crowd, because workshops
also play this role of providing a place for people to meet and discuss,
which is often perceived as even more useful than the actual technical
presentations. We therefore decided to include some advanced topics in
the program as well, so that everybody, including seasoned WR users and
developers, could learn something new.
White Rabbit (WR) is an extension of Ethernet which provides determinism
and a common notion of time to all nodes connected in the same network.
By determinism we mean a guaranteed upper bound in message transport
latency. The common notion of time is delivered using extensions to IEEE
1588 (PTP), currently undergoing a standardization effort. The accuracy
of this common notion of time is better than 1 nanosecond. All the basic
building blocks in WR are open source software, gateware and hardware.
The talk explains the basic concepts behind WR and provides context for
the more detailed talks which come later in the day.
WR in action: distributed synchronization concepts and demo
The presentation will start with a general discussion about distributed
synchronization concepts using the distribution of a Pulse Per Second
(PPS) over a WR network as an example. A short showcase of available WR
devices will follow. The demo will show how to setup a WR network from
scratch. Starting with a discussion about needed fiber cabling, through
the configuration of WR nodes and switches (introducing some
newly-developed web-based tools), to an overview of the basic
diagnostics in a WR network using standard monitoring and expert tools.
The talk will end with a short demo presenting how changes in fiber
temperature can affect the synchronisation between two nodes (aka "the
hot air gun demo").
Phase-compensated distribution of RF signals using WR (with demo)
Every node in a WR network is provided with a phase-aligned 125 MHz
reference. Having same reference clock phase everywhere enables
distribution of Radio Frequency clocks and other RF signals through
Direct Digital Synthesis (DDS). This talk will focus on a WR-based RF
distribution system capable of efficiently handling modulated RF
signals. A live demo will follow.
MIMO systems (with demo) and distributed oscilloscopes using WR
This presentation will focus on the WR network operating at CERN for
exchanging trigger pulses between a set of geographically distributed
instruments responsible for beam instability diagnostics in the LHC. The
system features low&fixed latency message distribution and can be
easily tailored to custom requirements. The presentation will be
followed by a demo of a small trigger distribution network.
Distributes oscilloscopes using WR
This talk will introduce the idea of utilising a WR network in order to
form an interconnected network of distributed oscilloscopes (and other
scientific instruments). The main goal is to leverage the sub-nanosecond
synchronisation and time distribution provided by WR to “negate” the
actual distance between the instruments and provide the user with a
unified view and control (e.g. for trigger sequencing and distribution)
of all interconnected instruments, as well as automatic discovery and
enumeration of newly connected
How to use the WR PTP Core to make your own WR nodes, advanced concepts
The White Rabbit PTP Core (WRPC) is the main element of every WR node.
It is an HDL implementation of a Gigabit Ethernet MAC including the full
White Rabbit synchronization stack. This talk will provide a
comprehensive description of the WRPC and its interfaces. We will
present how user-defined HDL modules can benefit from the timing
information provided by the core and how they can use the pipelined
Wishbone interface for sending application-specific Ethernet frames. We
will also see how the WRPC instantiation in your own WR node can be
simplified by using provided HDL wrappers for officially supported
boards and FPGA platforms.
Advanced diagnostics in a WR network
White Rabbit is an extension of a regular Ethernet network. The same way
you can diagnose off-the-shelf Ethernet switches and routers using the
Simple Network Management Protocol (SNMP), you can also diagnose timing
and data problems in your WR network. In this talk we will describe the
various SNMP objects that are exported by WR switches and WR nodes as
well as how they can be analysed using Nagios (an open-source SNMP
manager) to ensure correct operation of the network. Finally, we will
emulate various failures that may occur in a typical WR installation,
show how these can be detected and fixed.
Determinism in WR: priority handling and latency bounds with demo
This talk explains the mechanism to ensure determinism of message
transport latency in White Rabbit, the possibilities enabled by this
feature and its configuration. A professional IT tester will be used to
demonstrate how the deterministic message transport latency works.
Real-Time streaming of information using WR (with demo)
White Rabbit cores provide a streaming facility/layer that can be used
in WR Nodes - the WR
VHDL module. The WR Streamers take advantage of WR's features (i.e.
synchronization and determinism) to allow data streaming with low and
fixed latency. This streaming facility is a building brick of a system
that distributes the value of the magnetic field in real-time to clients
in different CERN accelerators. This talk explains the WR Streamers,
their integration into your design and their applications. The
demonstration will illustrate how the WR Streamers are used at CERN.
Calibration (with demo) and remote configuration of WR nodes
To ensure sub-nanosecond synchronization, the White Rabbit software
stack needs to estimate the communication link asymmetry. In this talk
we will introduce the White Rabbit link delay model to characterize
various factors that make the Master-to-Slave and Slave-to-Master link
latencies not equal. To model these asymmetries we will demonstrate the
calibration procedure that can be performed in the lab before the WR
infrastructure is deployed. We will also show how to use a Simple
Network Management Protocol (SNMP) to upload calibration parameters to
the WR nodes.
High-precision time and frequency distribution using WR
The talk explains the phase noise formalism for studying and optimizing
jitter through the use of Phase Locked Loops (PLL). We then move on to
apply these concepts in the context of WR, identifying places in a WR
link which impose constraints on any jitter optimization exercise, and
discussing how to design a very precise time and frequency transfer
system using WR.