National Instruments VXI Series, Getting Started

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Chapter 3 VXI Configuration Utility
VXIpc Controller for VxWorks 3-10 ni.com
Arbiter Timeout
An arbitration timeout feature is available on the VXIpc controller when it
is acting as the VMEbus arbiter. This feature applies only to a VXI Slot 0
VXIpc. By default, this option is disabled.
If you enable this feature, the timer begins when the arbiter circuit on the
VXIpc drives one of the BGOUT lines on the backplane. If no device takes
over the bus within the timeout limit, the BGOUT is removed and the bus
is either idle or granted to another requester.
User Window and Driver Window
The VXIpc controller driver requires the use of two PCI windows—a user
window and a driver window. Calling the
MapVXIAddress()
function
allocates regions of the user window to your application.
VXIpeek()
and
VXIpoke()
accesses are performed through this window. NI-VXI uses the
driver window to perform high-level functions such as
VXIin()
and
VXIout()
, and to access MITE registers on the VXIpc controller.
The windows are mapped to PCI base address registers and determine the
amount of PCI memory space the VXIpc requests from the PCI system
during initialization. You can set the window base, window size, and
whether the window resides above or below the 1 MB address space
boundary.
Window Size
The amount of space you can allocate for the user window is system
dependent. By changing the value of the
Size parameter, you can select the
size of the user window (minimum of 4 KB, maximum of 2 GB). The more
you increase the size of the user window, the larger the window you can
map in
MapVXIAddress()
.
If you change this setting, you must reconfigure the memory mapping
settings in
syslib.c
and recompile the VxWorks image. Refer to the
Step 3. Set up the VXIpc Controller with VxWorks section in Chapter 2,
Setup , for details on how to do this.
You can also disable this option. Disabling the user window causes the
VXIpc to request the minimum amount of address space on the PCI bus.
With the window disabled, you cannot perform any low-level function calls
such as
VXIpeek()
,
VXIpoke()
, and
MapVXIAddress()
.
The default setting for the user window is set at 64 KB. National
Instruments recommends you have a user window of at least this value.