Table of Contents
Advertisement
in its 16 least significant bits. When a 32-bit alignment of data is requested, two marker
words are inserted with the second one composed of the 16 most significant bits of the
specified data. No address word is to be inserted.
4.5.15 Use of Hit Registers for Conditional Execution of Stack Commands
VM-USB allows one to use hit registers (coincidence registers) to perform conditional
execution of any stack commands. To perform such a conditional execution, one must first
define a module to be read as a hit register module and then identify any of the subsequent
commands as conditional ones, while specifying the conditions.
A module is identified in the command stack as a hit register by setting bit 17 (value
0x20000) in the Mode Word. The data read from such a module are stored in a register and
used in subsequent conditional operations to verify if a desired condition is met. One may
have any number of hit registers defined, each overriding the latest hit word and providing a
new hit pattern for subsequent conditional readouts.
A command to be executed conditionally is identified in the command stack by setting bit 19
(value 0x80000) of its Mode Word. Additionally, one must specify in bits 22-23 (values
0x400000 and 0x800000) of the Mode Word the number of terms less one (i.e., zero
indicates one mask word) in the logical equation (condition) and supply the specified number
of 32-bit mask words. The mask words must follow the address word.
The command is executed when the following logical condition composed of up to fourfold
OR of 32-fold ANDs is met:
(BMask(1) AND HD = BMask(1)) OR
(BMask(2) AND HD = BMask(2)) OR
(BMask(3) AND HD = BMask(3)) OR
(BMask(4) AND HD = BMask(4)),
where HD represents the most recent hit data retrieved from a hit register and BMask(*) are
the (up to four) 32-bit mask words. Note that the command will be executed whenever in the
most recent hit register data all bits specified in any of the used Bit Masks are set. Note that
one can readily use more than four terms by repeating the same conditional command with a
set of different mask words.
4.5.16 Using Dynamical Block Sizing for Block Transfers
VM-USB allows one to perform block transfers with block lengths retrieved dynamically
from any of the VME devices. To use this feature, one must first specify which portion of the
retrieved data (field) contains the desired number of transfers to be performed. This is done
WIENER, Plein & Baus GmbH
30
www.wiener-d.com
Advertisement
Table of Contents
