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15-13
Stack Id
Event length (in 16 or 32-bit words depending on read type) including terminator words.
4. Event Data
5. Optional Event Terminator (user definable, 0xAAAA in firmware before 660007010
...
... Subsequent Events
...
Buffer Terminator
Second Buffer Terminator
Firmware 95000405 and later allows one to mix regular and scaler events in a common data
buffer. In a mixed buffer mode, the scaler data are identified by bit 15=1 of the Event Length
word.
Note that write operations performed in autonomous mode (data acquisition) do not return
data into the data stream.
The unpacking of the events must be done in accordance with the VME Stack that is
involved in generating the buffer.
In the Continuous (split-event) mode, when events span two or more buffers, no buffer
terminator is written.
For the direct access of the VME Command Generator (Interactive VME operations), no
header words are written and the In Packet contains only one event.
VM-USB has dedicated 2kWords-long event FIFO to compile events. To handle longer
events, VM-USB splits the long event into parts, each of which appears as a separate event in
the output buffer. The partial events are tagged by setting bit 12 of the Event Length word,
except for the last part. Also, only the last "installment" is terminated by the Event
Terminator word (s).
VM-USB has a provision to automatically switch the output buffer packing mode to Split-
Event mode, whenever the Event Length exceeds the length of the Integer-Event buffer.
Setting of bit 13 in the buffer header word indicates the fact of such a change.
With firmware 16000503 and the introduction of up to 8 executable stacks the structure of
the event header (specifying the number of words in the event) has been modified to identify
the stack ID associated with this event. The 3-bit stack ID is stored in bits 13-15 (counting
from 0) of the event header word. Unless a mixed-event option is selected for data buffering
(recommended for increased band width), the buffers will contain events with identical stack
IDs.
In interactive mode, VME Write command returns a single word, but only when this
command is the last command in the interactive stack. Note that this includes the case when
the write command is the only command in the stack. The returned word is "1" when the
WIENER, Plein & Baus GmbH
12
Continuation bit
0xFFFF
0xFFFF – firmware 66000701 and newer
33
11-0
Event length
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