This document defines the format of Raw Event Data within Euroball - ie the format of data generated by the electronics and passed to the data collectors. The format of full events generated within the event builder may (as in the case of Eurogam) be different.

It is assumed that compatibility with the Eurogam readout is necessary and hence the general format of the data follows the format described in the paper by J.Alexander DT32 bus specification Version 2 (edoc075).

In Eurogam all data sources connect to one DT32 bus which in effect acts as a hardware event builder. The Start Event token is generated within the Trigger module which is ensured to be the first data word within an event by the physical location of the Trigger module within the first VXI crate on the DT32 bus. Each ROCO outputs an End SubEvent token for each event and the End Event token is just the End SubEvent token generated by the last ROCO on the DT32 bus.

For Euroball it is required that there will be several DT32 bus chains and hence a more flexible system is needed. However there can be no radical departure from the defined 32 bit structure since this is a feature of the Eurogam readout system.

        Format of a data word

                      I xx I xxxxxx I xxxxxxxx I xxxxxxxxxxxxxxxx I
                        qq    item     group          data

        group 255 is used by the Trigger and ROCOs.
        items 1 => 47 are allocated to ROCOs with the last ROCO in the chain
        always being 47

        The Eurogam Start Event token has
                qq    = 11
                item  = 0x3f
                group = 0xff
                data  = event number

        and the End SubEvent token has

                qq    = 00    (good)   or  10  (ROCO detected error)
                item  = ROCO number
                group = 0xff
                data  = size of subevent in words (most significant 12 bits)
                      = least significant 4 bits contain copy of event number

For Euroball the requirement for more than one DT32 bus means that an alternative for the Trigger produced Start Event Token has to be found. Also as the requirement is analysed a more general system is desirable. Each ROCO should be as independant as possible and the ROCO only should be responsible for generation of the tokens.

Within the general format the address fields (group + item) allow data items to be uniquely identfied throughout the system. Thus it is possible to identify the source of data at any time during processing. This feature is a valuable diagnostic tool and is preserved in the following definitions.

The requirement for Euroball is that we define both a Start SubEvent token and an End SubEvent token where the term SubEvent here refers to the contribution to the total event from a single ROCO.

        Format of a token

                      | xxxx | xxxx | xxxxxxxx | xxxxxxxxxxxxxxxx |
                        flags  item    group          data

        Start SubEvent Token

                      | qq00 | xxxx | xxxxxxxx | xxxxxxxxxxxx | xxxx |
                               ROCO    group        word       event
                                         no         count      number


        End SubEvent Token

                      | q011 | xxxx | xxxxxxxx | xxxxxxxxxxxxxxxx |
                               ROCO    group        check sum
                                        no

This format assumes no more than 15 ROCOs on a single DT32 bus. The first in the chain MUST be ROCO Number = 1 and the last in the chain MUST be ROCO Number = 15. If there is only one ROCO on the DT32 bus then it WILL BE ROCO Number = 15.

The group = 0xf8 (248) is assigned to the first DT32 bus and groups 0xf9 (249), 0xfa (250) etc are assigned to the second and third DT32 bus. The maximum number of DT32 bus chains allowed is 8 and thus groups 248 to 255 are reserved for this purpose.

The qualifier bits in the Start SubEvent token will normally be set to zero but may be set by the ROCO to indicate that the data which follows should not be trusted and used to construct an event. For example the ROCO may use these bits to forward data being discarded following a VXI readout error.

The event number field is the low order 4 bits of the Trigger event number as broadcast throughout the system.

The word count field is the total number of data items (words) within the subevent and includes all the tokens.

The checksum is calculated as the twos complement 32 bit sum of all data words within the event including the start and end tokens. The 32 bit sum is converted into a 16 bit checksum by addition of the most significant and the least sigificant 16 bits. For the purpose of the sum the value of the checksum field is taken to be zero.

The qualifier bit in the End SubEvent token will initially be set to zero but may be set to one by the event collector to indicate a checksum failure.

Each SubEvent MUST also contain a EventNumber data item which MUST immediately follow the Start SubEvent token.

        EventNumber Data Item

                      | qq01 | xxxx | xxxxxxxx | xxxxxxxxxxxxxxxx |
                               ROCO    group       event number
                                no

The event number will be reconstructed using the method as described in the document Event Number generation within Euroball. The qualifier bits will normally be set to zero but qq=10 will be used to indicate that a single step resynchronisation occurred and qq=11 will be used to indicate that a multi step resynchronisation occurred.

Each SubEvent MAY also contain a EventNumber Extension data item which if it is present MUST immediately follow the EventNumber data item. The EventNumber Extension extends the event number to 32 bits as described in the document Event Number generation within Euroball.

        EventNumber Extension Data Item

                      | qq10 | xxxx | xxxxxxxx | xxxxxxxxxxxxxxxx |
                               ROCO    group       event number
                                        no          extension

The qualifier bits will normally be set to zero.

The Eurogam Trigger module currently generates data using group 255. The format of Trigger data words are

                      | 1111 | xxxx | 11111111 | xxxxxxxxxxxxxxxx |
                               0-15    group          data

Data of this format will be considered as a normal data item for group 255. For Euroball a redesign of the trigger module will allow use of a group other than 255. Group 247 has been reserved for the Euroball trigger.

Using the terms Start Event and End Event for the collection of all the SubEvents which can be readout on a single DT32 bus we have

Start Event Token     | xx00 | xxxx | 11111xxx | xxxxxxxxxxxxxxxx

and

End Event Token       | xx11 | 1111 | 11111xxx | xxxxxxxxxxxxxxxx

Where x is a do-not-care bit.

To implement these requirements the firmware within the ROCOs must perform the following tasks

These programming options allow virtually any protocol to be generated for the Tokens within the general outline format.