wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

24-4 Industrial Communication Systems
Moreover, an ARINC 429 transmitter can transmit to a maximum of 20 receivers. While the ARINC
429 data bus provides high determinism, point-to-point wiring has become a major problem in systems
composed of multiple emitting units.
24.4 Integrated Modular Avionics
The IMA concept has introduced the sharing of execution and communication resources. IMA hardware
architecture, as described in the standard ARINC 651 [ARI91], is represented in Figure 24.3.
Execution and communication resources are described as standard LRMs that are installed in common
cabinets. Three types of modules have been designed: core modules for application execution, input–
output modules for communications with non-IMA equipment (existing LRUs), and gateway modules
for communicating among cabinets. The ARINC 659 back plane data bus standard has been used for
communication between modules hosted in the same cabinet [ARI93]. Communication among cabinets
needs new aircraft data buses such as ARINC 629 [ARI99].
ARINC 653 [ARI97] describes how many avionics subsystems can share the execution resources of
an IMA architecture. In an ARINC 653 environment, an avionics subsystem is no longer implemented
on a dedicated CPU or LRU but is viewed as a partition, to which is assigned a time window to execute
its code on a shared core processing module (CPM). Each partition becomes a virtual CPU or LRU.
A robust partitioning concept is introduced to guarantee isolation between subsystems running on the
same execution computer. Spatial isolation is guaranteed by protecting the address space of each partition
(for example, by a memory management unit). Temporal isolation is based on the static allocation
of CPU time to each partition. Time partitioning guarantees that each user partition obtains a slice of
time for execution as determined by the integrator as a worst-case execution time (easier to evaluate for
systems that have mostly periodic processes). The main objective is to guarantee that an avionic subsystem
running in a given partition will have no effect on other subsystems running in other partitions.
Partitions communicate with each other by exchanging messages through communication ports. Two
types of communication ports can be used: sampling ports (periodic data—only the last value of data
is stored) and queuing ports (all the values of data are stored). A logical channel concept is used to link
communicating ports (multicast scheme—1 emitter and N receivers) independently of the underlying
data bus or network stack. Mechanisms are needed in order to schedule inputs–outputs according to the
needs of each partition (for example, port sizes and depths must be determined on a worst case communication
basis). In conclusion, the ARINC 653 interface between application software and the run-time
Backplane
Backplane
APEX/C APEX/C APEX/C APEX/C APEX/C APEX/C APEX/C APEX/C
F1
F2
F1
F3
F1
F2
F3
F1
F3
F1
F3
F1
F2
F2
F1
F1
F3
Aircraft data bus
ARINC 429
API
API
Eq F1
Eq F2
F1
F3
ARINC 429
Eq F3
FIGURE 24.3
IMA avionics architecture.
© 2011 by Taylor and Francis Group, LLC