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GUIDE TO LIST MODE DATA ACQUISITION WITH VM-USB
VM-USB is intended for use in list mode data acquisition, where it performs sequences of
desired VME operations pursuant to stack(s) stored in it, upon receipt of event trigger. VM-
USB then formats the data read form the VME bus and buffers them in a data buffer. When
the buffer is full, VM-USB transfers its content to the In FIFO of the USB controller IC for
readout by host software.
To set up VM-USB for data acquisition in list mode the following steps are advised:
1. Build the regular VME command stack by adding all the desired simple and complex
commands to it. One must make sure that the stack sequence will clear all VME
modules. It is recommended to first execute the stack from the host software to verify
that it performs as intended. For this purpose the libxxusb library function
xxusb_stack_execute can be used. For firmware 66000701 and newer, insert one or
more marker words at the end of the stack to mark the end of an event in the data
stream.
2. Load the stack into the VM-USB memory, e.g., by calling the libxxusb library
function xxusb_stack_write. It is recommended to read back the stack (function
xxusb_stack_read), to verify that the stack is correctly stored.
3. When the setup calls for it, build and load the auxiliary (scaler) stack and define the
readout mode and frequency.
4. Set the trigger delay (time from the receipt of an event to the commencement of the
stack execution).
5. If VM-USB is not the slot 1 controller, set up the bus request level, by writing the bus
request level code into bits 12-14 of the Global Register.
6. Set up event termination mode. By default, VM-USB terminates every event by one
terminator word 0x5555, with the second word 0xAAAA being optional – applicable
to old firmware only. For firmware 0x66000701 and newer, insert a suitable marker
word into the command stack to mark the end of an event.
7. Set up buffering mode and data buffer length by writing a suitable 5-bit code into bits
0-4 of the Global Mode Register. The default is buffer length of 13k words and events
fitting into one buffer.
8. Set buffer header option. By default, VM-USB writes one buffer header word
containing information on the number of events in the buffer, buffer type (regular, or
periodic auxiliary), and the buffer termination mode (regular or watchdog).
9. Start acquisition by setting bit 0 of the Action Register to 1. End acquisition by
resetting this bit to "0". While in acquisition mode, the host software is expected to
read the USB port In FIFO in a loop, to empty it and make space for subsequent
events.
WIENER, Plein & Baus GmbH
35
www.wiener-d.com
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