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Bit 3 of the Action Register is a write-only bit linked to the SYSRES line, active when VM-
USB is a slot one controller. When set to "1" VM-USB generates SYSRES. When set to "0",
the SYSRES is cancelled.
Bit 4 (write-only) of the action register is used to trigger scaler readout when VM-USB is in
data acquisition mode. This interactive mode of the scaler readout combines with the two
automatic readout modes (event-based and timer-based) on "whichever-comes-first" basis.
3.2 VME Command Generator / EASY-VME (Address = 4 / 0x4)
The VME Command Generator decodes lists of coded VME commands, submits the
commands for execution in VME cycles, and causes the received data, if any, to be stored in
a 4kB event memory (FIFO). At the end of the list (end of an event), the content of the event
FIFO is compiled into the main data buffer (up to 26 kB), for a subsequent transfer to the
USB controller. The VME Command Generator receives coded data either directly from the
host (in interactive or Easy-VME mode), or reads it from the VME Command Stacks (in
autonomous data acquisition mode). The structure of the list is identical in both modes of
operation and is discussed in detail further below. An integral part of the VME command is
the VME address of a target register/memory location. In the context of the discussed VM-
USB architecture, this VME address is a secondary address and its space includes the internal
VME address space of VM-USB, associated with the internal register file of VM-USB.
3.3 VME Command Stacks
VME Command Stacks (VCS) are used to store suitably formatted lists or sequences of VME
Commands to be performed in response to event trigger signals while VM-USB is operating
in autonomous data acquisition mode of operation (DAQ mode). In this mode of operation,
VM-USB issues VME commands, reads the data received in response to them, and buffers
the data in a data buffer. When the buffer (up to 26kB) is full, VM-USB dumps it to the FIFO
of the USB controller IC for the retrieval by the host. It is this data buffering that allows one
to take advantage of the superior band width of the USB2 interface in bulk transfer mode and
to achieve throughputs in excess of 30 Mbytes/s.
Starting with firmware 16000503 the number of stacks that could be defined was increased
from 2 to 8. The new firmware allows one to define up to 8 stacks, with Stack ID=0-7,
within the allocated memory of 2kBytes = 1kWords. The starting addresses of stacks can be
set arbitrarily. While stacks with ID=2-7 are dedicated to interrupt handling, stacks with
ID=0 and 1 are of dual use. Unless the latter stacks are used for interrupt handling, they
default to a regular stack with ID=0, executed upon trigger pulse (NIM I1 or USBStart) and
the periodic stack with ID=1 (scaler stack).
When not working in DAQ mode, the VME command stacks can also be executed by the
VME Command Generator (VCG). Chapter 4.4 provides details about the VCS and VCG
stack structure and how to write the stack to the VM-USB. Stack instructions and examples
are shown in chapter 4.5.
While any arbitrary block of data can be stored in the stack memory and then read back, all
stacks are expected to contain properly encoded sequences of VME operations and their
associated options, such that they can be meaningfully decoded by the VME Command
Generator module and submitted for execution, while VM-USB operates in autonomous data
acquisition mode.
WIENER, Plein & Baus GmbH
15
www.wiener-d.com
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