Chapter 6 NI-VXI Configuration Utility
© National Instruments Corporation 6-17 PCI-MXI-2 for Linux
beneficial to disable the MXI-2 auto retry feature. With this feature
disabled, you can lower the MXI Bus Timeout because there will be no
delay due to the inward cycles being retried.
Note The PCI-MXI-2 has a limit on the number of automatic retries they will perform on
any one cycle. If the limit is exceeded and the PCI-MXI-2 receives another retry, it will
pass a retry back to the MXIbus even though the Enable MXI-2 Auto Retry checkbox is
checked.

A24/A32 Write Posting

This field determines whether to enable write posting for incoming slave
accesses to A24/A32 VXI/VME shared RAM. By default this option is
disabled—the Enable A24/A32 Write Posting checkbox is cleared.
Enabling write posting will increase the throughput of your inward cycles.
However, you should not enable write posting unless the destination of your
inward A24/A32 cycles is onboard RAM, because cycles to onboard RAM
will always complete successfully.
PCI Bus
The following sections describe the opt ions for the PCI Bus portion of this
editor.

User Window and Driver Window

The PCI-MXI-2 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 registers on the PCI-MXI-2 and
VXI/VME-MXI-2.
The windows are mapped to PCI base address registers and determine the
amount of PCI memory space the PCI-MXI-2 requests from the PCI system
during initialization.