Table of Contents
Advertisement
A jump table, located just above the 68000 exception vectors, is maintained in EPROM.
This jump table provides linkage between application specific code and Message-Based
Interface system services.
ASCII command strings arriving over the VXI interface are placed into a primary input
queue. Each position in the queue holds 16-bits of data. V X I status information (like
"EOI asserted") is encoded into the upper 8 bits of each piece o f data. These 16-bit
values are referred to as "raw data", or "raw characters". Application specific command
strings are placed into a secondary queue. A l l VXI status information in the upper 8 bits
is preserved. A suite of functions is available to retrieve raw and stripped characters from
the input queues, and to query the VXI status bits.
A heap is maintained, and its overall size is programmable. The default size is 4Kb. The
Message-Based Interface provides memory management functions that allocate and
reclaim blocks of storage from this heap.
The Message-Based Interface maintains a global symbol table. A t run time, it is used to
bind identifiers (i.e. ASCII strings) to the absolute addresses of blocks o f application
specific code.
4.2.2 C a l l i n g Conventions
All Message-Based Interface system services obey C-language calling conventions as
specified by the Intermetrics C Cross Compiler. See the Cross Compiler's Manual for
complete details.
4.2.3 V X l b u s Interface
The VXI interface is implemented with dual-port RAMs. T h e RAMs and interface I/O
support circuitry are located in this area.
User space is the upper half of memory. The user may use this space in conjunction with
any user supplied code and circuitry to implement special functions and handle special
needs.
All of the I/O ports are located in the local bus space. Reads and writes to this area
cause transfers across the local bus. These cause reads or writes to the I/O ports.
4.2.4 T i m e r
A timer is used to maintain a real time clock with the time since power-up initialization.
A set of routines are provided to allow the user access to the timer.
4-2
Advertisement
Table of Contents
