RCS20 M:N Redundancy Switch
Revision 15
Remote Operations
MN-RCS20 and CD-RCS20
A–9
Volatile Section is. This count is used by M&C developers to index into the start of the volatile section use
this count.
When new features are added to Radyne equipment, the control parameters are appended to the end of
the non-volatile section, and status of the features, if any, are added at the end of the volatile section. If a
remote M&C queries two pieces of Radyne equipment with different revision software, they may respond
with two different sized packets. The remote M&C MUST make use of the non-volatile count value to
index to the start of the volatile section. If the remote M&C is not aware of the newly added features to the
Radyne product, it should disregard the parameters at the end of the non-volatile section and index to the
start of the volatile section.
If packets are handled in this fashion, there will also be backward-compatibility between Radyne
equipment and M&C systems. Remote M&C systems need not be modified every time a feature is added
unless the user needs access to that feature.
A.1.7
Flow Control and Task Processing
The original packet sender (the M&C computer) relies on accurate timeout information with regard to
each piece of equipment under its control. This provides for efficient bus communication without
unnecessary handshake overhead timing. One critical value is designated the Inter-Frame Space (FS).
The Inter-Frame Space provides a period of time in which the packet receiver and medium (control bus
and M&C computer interface) fully recover from the packet transmission/reception process and the
receiver is ready to accept a new message. The programmed value of the Inter-Frame Space should be
greater than the sum of the "turnaround time" and the round-trip (sender/receiver/bus) propagation time,
including handshake overhead. The term "turnaround time" refers to the amount of time required for a
receiver to be re-enabled and ready to receive a packet after having just received a packet. In flow control
programming, the Inter-Frame Space may be determined empirically in accord with the system
configuration, or calculated based on established maximum equipment task processing times.
Each piece of supported equipment on the control bus executes a Radyne Link Level Task (RLLT) in
accordance with its internal hardware and fixed program structure. In a flow control example, the RLLT
issues an internal "message in" system call to invoke an I/0 wait condition that persists until the task
receives a command from the M & C computer. The RLLT has the option of setting a timeout on the
incoming message. Thus, if the equipment does not receive an information/command packet within a
given time period, the associated RLLT exits the I/0 wait state and takes appropriate action.
Radyne equipment is logically linked to the control bus via an Internal I/O Processing Task (IOPT) to
handle frame sequencing, error checking, and handshaking. The IOPT is essentially a link between the
equipment RLLT and the control bus. Each time the M&C computer sends a message packet, the IOPT
receives the message and performs error checking. If errors are absent, the IOPT passes the message to
the equipment's RLLT. If the IOPT detects errors, it appends error messages to the packet. Whenever an
error occurs, the IOPT notes it and discards the message; but it keeps track of the incoming packet. Once
