Structure Of The In Packets - Wiener VM-USB User Manual

A
0000
0009
0000
0020
7800
FFFF
AAAA
0109
0000
0121
7800

4.6 Structure of the IN Packets

The General Output Buffer is associated with Endpoint 6 of the USB2 controller IC, which is
configured as a 512 byte deep FIFO. This endpoint is configured for bulk transfer and one
can specify lengths of buffers to be read of any length (up to 26 kBytes) compatible with the
VM-USB functionality. All data supplied by the VM-USB is to be read from the Endpoint 6.
While reading, it is important to specify the length of the buffer not shorter than the length of
the actual data buffer written by the VM-USB into this endpoint.
The structure of data retrieved in conjunction with direct requests for data addressed to the
Register Block and to the VME Stacks is straightforward, such that the buffer consists only
of the requested data.
The data buffers read during the data acquisition process have a structure depending on the
buffer filling mode selected by bit 4 of BuffOpt code specified in the Global Register. The
default filling is such that the buffer contains only complete events (bit 4 of BuffOpt=0). On
the other hand, when bit 4 of BuffOpt is set, continuous filling is selected allowing single
events to span two or more buffers. Whenever the size of a single event exceeds the declared
size of the data buffer and the filling mode is set for complete events, the filling mode
switches to continuous mode, with this fact tagged by setting of the bit 13 of the buffer
header word. For the Complete Event Mode, the data buffer has the following structure:
1. Header word
15
LB
LB= Last Buffer, is 1 if the buffer is last buffer of a run
Scaler=Scaler Buffer, is 1 if the data in the buffer is from the scaler stack
Cont= Indicates the module switched to a continuous mode
MB= Indicates that the event data spans several buffers
NE=Number of Events, indicates how many events are in the buffer
nd
2. Optional 2
3. Event Header
WIENER, Plein & Baus GmbH
// number of lines (decimal 11)
// the starting address to store the stack within the stack buffer
// AM / write mode (bits 0-15)
// BLT / special modes (bits 16-31)
// VME address (bits 0-15)
// VME address (bits 16-31)
// data (bits 0-15)
// data (bits 16-31)
// AM / write mode (bits 0-15), bit 8=1 for read
// BLT / special modes (bits 16-31)
// VME address (bits 0-15), A0=1 for 16bit
// VME address (bits 16-31)
14
Scaler
Header Word Bits 0-11 represent the number of words in the buffer.
13 12
Cont MB
32
11-0
NE
www.wiener-d.com