Schedulability analysis of CAN with non-abortable transmission requests

Abstract

Abstract-The analysis of the real-time properties of an embedded communication system relies on finding upper bounds on the Worst-Case Response Time (WCRT) of the messages that are exchanged among the nodes on the network. The classical WCRT analysis of Controller Area Network (CAN) implicitly assumes that at any given time, each node is able to enter its highest priority ready message into arbitration. However, in reality, CAN controllers may have some characteristics, such as nonabortable transmit buffers, which may break this assumption. This paper provides analysis for networks that contain nodes with non-abortable transmit buffers, as well as nodes that meet the requirements of the classical analysis. The impact on message WCRTs due to a limited number of transmission buffers with non-abortable behaviour is examined via two case-studies.

Extending response-time analysis of mixed messages in CAN with controllers implementing non-abortable transmit buffers

“…Later on, Davis et al [3] refuted, revisited and revised the analysis developed by Tindell et al The queueing polices implemented by the CAN device drivers and communications stacks, internal organization and hardware limitations of CAN controllers may have significant impact on the timing behavior of CAN messages [4]. A few examples of such limitations are controllers implementing FIFO and work-conserving queues [4,5], limited number of transmit buffers [6,7,8], copying delays in transmit buffers [6,8], transmit buffers supporting abort requests [7], the device drivers lacking abort request mechanisms in transmit buffers [4,6,7,8] and protocol stack prohibiting transmission abort requests in some configurations as in the case of AUTOSAR [9].…”

“…However, the analysis in [2,3] assumes that CAN controllers have very large number of transmit buffers. However, most CAN controllers have small number of transmit buffers [6,4]. If all such buffers are occupied by lower priority messages, a higher priority message released in the same controller may suffer from priority inversion (it will be discussed in Section 3) [2,7,8].…”

Analysis and optimization of message acceptance filter configurations for controller area network (CAN)

“…Further work has explored the issues that can arise if the prioritybased arbitration mechanism is circumvented, for example by the use of non-abortable transmit bufers [20], or FIFO queues [8,9]. In practical applications, using an optimal priority assignment policy is not in itself enough, since the ordering generated could leave the system only just schedulable, and thus vulnerable to deadline misses in the event that there is an increase in errors on the bus.…”

A review of fixed priority and EDF scheduling for hard real-time uniprocessor systems

“…Precise schedulability analysis has been derived for Controller Area Networks [36] that makes certain assumptions in terms of the behaviour of the nodes connected to the bus (perfect priority queues); however, in practice these assumptions may not always hold. Recent work has sort to address particular features of the hardware such as nonabortable transmit requests [51], and the fact that FIFO queuing policies are often used [30], [31]. These extensions make the analysis more flexible and better suited to commercial use.…”