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over the VXlbus on request. I t provides primitive security capabilities. Another flag is
used to identify this as a user or a breadboard block. There are two flags reserved for
future use. Four bits are available for the user to identify different types of blocks.
The Block Checksum is used to verify integrity of the block. I t is checked during power-
up initialization.
Block Size i s used f o r maintaining the Non-Vol structure. T h e user can store a
description of each block. Commands can be used to cause this information to be sent
over the V X I . T h e information to be stored goes i n the data area. T h e type o f
information can be just about anything the user wants to store.
There is a set o f commands available from the VXlbus to manipulate the Non-Vol
memory. T h e standard Non-Vol memory size is 16K bytes. T h e system block size is
about 3/4 K bytes.
4.3.3.1 The System Area
The system area maintains a variety of Non-Vol records for operation of the system.
The user can specify a board configuration by selecting a port, value and a mask. When
that is specified, it is stored in Non-Vol. T h e system reads the board configuration at
power-up, and will report i f any configurations do not match.
Initial port values can be specified and stored in Non-Vol. These cause values other than
the default jumper values to be setup shortly after power-up.
If the user wants to change some of the initial values of the VXI registers, they can be
stored i n Non-Vol. A s the system powers up, these values w i l l be placed i n the
appropriate registers (see Appendix B).
The user can specify a number of vectors for asynchronous events. These vectors can be
stored in Non-Vol and setup as the system is powering up.
The user can specify the size of the input queue, the secondary input queue and the output
queue. These sizes can be stored in Non-Vol and used to setup the queues at power-on
initialization.
User code can be saved in Non-Vol so it can be used as the system is powered-up or as
part of the main loop without down loading code each time.
The interface software uses the system block to hold information to customize the
operation o f the interface. Information saved i n the system block is shown in the
structure nv_sys in the nv.h header file. Here is a reproduction of that structure (For the
actual structure for your version of the firmware, look at nv.h on the supplied diskette).
4-7
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