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  • Furunäs Åkesson, Johan, et al. (författare)
  • Interprocess communication utilising special purpose hardware
  • 2001
  • Licentiatavhandling (övrigt vetenskapligt)abstract
    • Real-Time Systems are computer systems with constraints on the timing of actions. To ease the development and maintenance of application software, Real-time Systems often make use of a Real-Time Operating System (RTOS). Its main task is scheduling of application processes (tasks). Other functions can be interprocess communication, interrupt handling, memory management etc.Sometimes it is hard (or even impossible) to meet the time constraints specified for a real-time system, resulting in an incorrectly functioning application. A possible remedy is to redesign the system by upgrading the processor and/or remove functionality, etc. An alternative solution could be the use of a special purpose hardware accelerated RTOS. The aim of such an accelerator is to speedup RTOS functions that impose big overhead i.e. to reduce the kernel overhead by offloading the application processor. Accordingly, the processor gets more time for executing application software, and hopefully the time constraints can be met. The main drawback is the cost of extra hardware.This thesis presents results from implementing RTOS functions in hardware, especially interprocess communication (IPC) functions. The types of systems considered are uniprocessor and shared memory multiprocessor real-time systems.IPC is used in systems with co-operating processes. The operating systems on the market support a large variation of IPC mechanisms. We will here present and evaluate three different IPC implementations. The first is an extended message queue mechanism that is used in commercial robot control applications. The second is the signal mechanism in OSE, a commercial RTOS predominantly used in telecommunication control applications, and the third is the semaphore and message queue mechanisms supported by the leading commercial RTOS VxWorks. All the implementations are based on a pre-emptive priority-based hardware real-time kernel accelerator.We show that it is not optimal, practical or desirable to implement every kernel function into hardware, regarding systems in the scope of this thesis. However, an accelerator allows new functionality to be implemented. We illustrate this by implementing a message queue mechanism that supports priority inheritance for message arrival in hardware, which is too expensive to implement in software. Also, we show that substantial speedups are possible, and that a crucial mechanism in achieving speedup is the accelerator-processor interconnect. We further note that application speedups are possible, even in cases with an IPC-mechanism slow-down. The main reasons for this is that the accelerator can off-load the processor by handling the RTOS timing mechanism (clock-ticks), reducing the RTOS code to be executed on the processor, and handling interrupts.
  • Åkesson, Karolina, et al. (författare)
  • Kynurenine pathway is altered in patients with SLE and associated with severe fatigue
  • 2018
  • Ingår i: Lupus Science and Medicine. - : BMJ Publishing Group Ltd. - 2053-8790 .- 1625-9823. ; 5:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Objective: Fatigue has been reported as the most disturbing symptom in a majority of patients with SLE. Depression is common and often severe. Together these symptoms cause significant morbidity and affect patients with otherwise relatively mild disease. Tryptophan and its metabolites in the kynurenine pathway are known to be important in several psychiatric conditions, for example, depression, which are often also associated with fatigue. We therefore investigated the kynurenine pathway in patients with SLE and controls.Methods: In a cross-sectional design plasma samples from 132 well-characterised patients with SLE and 30 age-matched and gender-matched population-based controls were analysed by liquid chromatography tandem mass spectrometry to measure the levels of tryptophan and its metabolites kynurenine and quinolinic acid. Fatigue was measured with Fatigue Severity Scale and depression with Hospital Anxiety and Depression Scale. SLE disease activity was assessed with Systemic Lupus Erythematosus Disease Activity Index (SLEDAI).Results: The kynurenine/tryptophan ratio, as a measure of indoleamine 2,3-dioxygenase (IDO) activity, was increased in patients with SLE. Patients with active disease (SLEDAI >= 6) showed lower tryptophan levels compared with controls (54 mu M, SD=19 vs 62 mu M, SD=14, p=0.03), although patients with SLE overall did not differ compared with controls. Patients with SLE had higher levels of tryptophan metabolites kynurenine (966 nM, SD=530) and quinolinic acid (546 nM, SD=480) compared with controls (kynurenine: 712 nM, SD=230, p=0.0001; quinolinic acid: 380 nM, SD=150, p=0.001). Kynurenine, quinolinic acid and the kynurenine/tryptophan ratio correlated weakly with severe fatigue (r(s)=0.34, r(s)=0.28 and r(s)=0.24, respectively) but not with depression.Conclusions: Metabolites in the kynurenine pathway are altered in patients with SLE compared with controls. Interestingly, fatigue correlated weakly with measures of enhanced tryptophan metabolism, while depression did not. Drugs targeting enzymes in the kynurenine pathway, for example, IDO inhibitors or niacin (B12) supplementation, which suppresses IDO activity, merit further investigation as treatments in SLE.
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