User manual

DMA Programming

Examples

Appendix

This appendix contains two example programs for using the DMA

controllers on the VXI-MXI-2. If you are using a version of the

National Instruments NI-VXI software that has remote DMA controller

functionality, this information is not necessary because you can make

use of the VXI-MXI-2 module’s DMA controllers from the NI-VXI

high-level function calls.

Overview of Programming Examples

The DMA controllers each have registers that define the source and

destination of the data. Data is always transferred from the source to the

destination during a DMA operation. The DMA controllers can transfer

data between devices located on different buses—VMEbus, MXIbus,

and DRAM onboard the VXI-MXI-2—as well as between devices

located on the same bus. The only limitation regarding location of the

devices is that MXIbus synchronous burst transfers cannot be used for

either the source or destination when both devices are located on the

MXIbus. The source and destination can each use differing data widths,

address spaces, and transfer types (single or block) during a DMA

operation. Detailed descriptions of each DMA register can be found in

the VXIbus A24/A32 Registers section of Chapter 5, Register

Descriptions.

The only difference between the two examples in this appendix is that

Example 1 does not make use of the DMA interrupt; Example 2 does

show this functionality. The examples use pseudo code that mostly

resembles the C language. Constant numbers in the examples preceded

are in hexadecimal notation. Both examples contain the two

functions write and read. These are meant to represent the method

for performing VMEbus or MXIbus data transfers to (write) and from

(read) devices.