Abstract
The IEC 61499 standard provides an executable model for distributed control systems in terms of interacting function blocks. However, the current IEC 61499 standard lacks appropriate timing semantics for the specification of timing requirements, reasoning on timing properties at the model level, and for the timing verification of a specific deployment. In this paper we address this fundamental shortcoming by proposing Real-Time-4-FUN, a real-time semantics for IEC 61499. The key property is the preservation of non-determinism, allowing us to reason on (and verify) timing properties at the model level without assuming any specific scheduling policy or stipulating specific order of execution for the deployment. This provides for a clear separation of concerns, where the designer can focus on properties of the application prior to, and separately from, deployment verification. The proposed timing semantics is backwards compatible to the current standard, thus allow for reuse of existing designs. The transitional property allows timing requirements to propagate to downstream sub-systems, and can be utilized for scheduling both at device and network level. Based on a translation to RTFM-tasks and resources, IEC 61499 models can be analyzed, compiled and executed. As a proof of concept the timing semantics has been experimentally implemented in the RTFM-core language and the accompanying (thread based) RTFM-RT run-time system.

Abstract
Robustness, real-time properties and resource efficiency are key properties to embedded devices of the CPS/IoT era. In this paper we propose a language approach RTFM-core, and show its potential to facilitate the development process and provide highly efficient and statically verifiable implementations. Our programming model is reactive, based on the familiar notions of concurrent tasks and (single-unit) resources. The language is kept minimalistic, capturing the static task, communication and resource structure of the system. Whereas C-source can be arbitrarily embedded in the model, and/or externally referenced, the instep to mainstream development is minimal, and a smooth transition of legacy code is possible. A prototype compiler implementation for RTFM-core is presented. The compiler generates C-code output that compiled together with the RTFM-kernel primitives runs on bare metal. The RTFM-kernel guarantees deadlock-lock free execution and efficiently exploits the underlying interrupt hardware for static priority scheduling and resource management under the Stack Resource Policy. This allows a plethora of well-known methods to static verification (response time analysis, stack memory analysis, etc.) to be readily applied. The proposed language and supporting tool-chain is demonstrated by showing the complete process from RTFM-core source code into bare metal executables for a lightweight ARM-Cortex M3 target.

Abstract
The mainstream of embedded software development as of today is dominated by C programming. To aid the development, hardware abstractions, libraries, kernels and lightweight operating systems are commonplace. Such kernels and operating systems typically impose a thread based abstraction to concurrency. However, in general thread based programming is hard, plagued by race conditions and dead-locks. For this paper we take an alternative outset in terms of a language abstraction, RTFM-core, where the system is modelled directly in terms of tasks and resources. In compliance to the Stack Resource Policy (SRP) model, the language enforces (well-formed) LIFO nesting of claimed resources, thus SRP based analysis and scheduling can be readily applied. For the execution onto bare-metal single core architectures, the rtfm-core compiler performs SRP analysis on the model and render an executable that is deadlock free and (through RTFM-kernel primitives) exploits the underlying interrupt hardware for efficient scheduling. The RTFM-core language embeds C-code and links to C-object files and libraries, and is thus applicable to the mainstream of embedded development. However, while the language enforces well-formed resource management, control flow in the embedded C-code may violate the LIFO nesting requirement. In this paper we address this issue by lifting a subset of C into the RTFM-core language allowing arbitrary control flow at the model level. In this way well-formed LIFO nesting can be enforced, and models ensured to be correct by construction. We demonstrate the feasibility by means of a prototype implementation in the rtfm-core compiler. Additionally, we develop a set of running examples and show in detail how control flow is handled at compile time and during run-time execution. © 2015 IEEE.

Abstract
The IEC 61499 standard provides means to specify distributed control systems in terms of function blocks. The execution model is event driven (asynchronous), where triggering events may be associated with data (and seen as a message). In this paper we propose a low complexity implementation technique allowing to assess end-to-end response time of event chains spanning over a set of networked devices. In this paper we develop a method to provide safe end-to-end response time taking both intra- and inter-device delivery delays into account. As a use case we study the implementation onto (single-core) ARM-cortex based devices communicating over a switched Ethernet network. For the analysis we define a generic switch model and an experimental setup allowing us to study the impact of network topology as well as 802.1Q quality of service in a mixed critical setting. Our results indicate that safe sub millisecond end-to-end response times can be obtained using the proposed approach. © 2015 IEEE.

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