• IEMEK Journal of Embedded Systems and Applications
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• v.15 no.4
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• pp.177-187
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• 2020

Virtualization with hypervisors is one of emerging topics in multicore processors for space. Hypervisors are software layers to make several independent virtualized environments on one processor. Since all hardware resources are virtualized and distributed only by hypervisors, overall performance of processors can be improved by fully utilizing the resources. However at the same time, there are overheads for virtualizing and distributing hardware resources. Satellites are one of hard real time systems, and performance degradation with overheads should be analyzed thoroughly. Previous research on the overheads focused on single core systems. Even the overheads were analyzed in multicore systems, SMP environment was not fully included. This paper builds SMP environment with XtratuM, one of hypervisors for space missions, and analyzes performance degradation with overheads. Two boards of GR712RC with 2 LEON3FT CPUs and GR740 with 4 LEON4 CPUs are used in experiments. On each board, SMP benchmark functions are executed on SMP environment with XtratuM and on that without XtratuM respectively. Results are analyzed to find timing characteristics including overheads. Finally, applicability of the XtratuM to flight software in SMP is also reviewed.

• IEMEK Journal of Embedded Systems and Applications
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• v.14 no.1
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• pp.51-61
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• 2019

There are strict evaluation processes before using new processors to satellites. Engineers evaluate processors from various viewpoints including specification, development environment, and cost. From a viewpoint of computation power, manufacturers provide benchmark results with processors, and engineers decide which processors are adequate to their satellites by comparing the benchmark results with requirements of their satellites. However, the benchmark results depends on a test environment of manufacturers, and it is quite difficult to achieve similar performance in a target environment. Therefore, it is necessary to evaluate the processors in the target environment. This paper compares performance of a processor, AT697F/LEON2, in software testbed (STB) with three development boards of XC2V/LEON3, GR712RC/LEON3, and GR740/LEON4. Seven benchmark functions of Dhrystone, Stanford, Coremark, Whetstone, Flops, NBench, and MiBench are selected. Results are analyzed with hardware and software properties: hardware properties of core architecture, number of cores, cache, and memory; and software properties of build options and compilers. Based on the analysis, this paper describes a guideline for choosing processors for next generation satellites.

• Communications of the Korean Mathematical Society
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• v.38 no.3
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• pp.733-740
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• 2023

Let R be a commutative ring and M be an R-module. The dimension graph of M, denoted by DG(M), is a simple undirected graph whose vertex set is Z(M) ⧵ Ann(M) and two distinct vertices x and y are adjacent if and only if dim M/(x, y)M = min{dim M/xM, dim M/yM}. It is shown that DG(M) is a disconnected graph if and only if (i) Ass(M) = {𝖕, 𝖖}, Z(M) = 𝖕 ∪ 𝖖 and Ann(M) = 𝖕 ∩ 𝖖. (ii) dim M = dim R/𝖕 = dim R/𝖖. (iii) dim M/xM = dim M for all x ∈ Z(M) ⧵ Ann(M). Furthermore, it is shown that diam(DG(M)) ≤ 2 and gr(DG(M)) = 3, whenever M is Noetherian with |Z(M) ⧵ Ann(M)| ≥ 3 and DG(M) is a connected graph.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.6
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• pp.467-478
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• 2020

Hypervisor virtualize hardware resources to utilize them more effectively. At the same time, hypervisor's characteristics of time and space partitioning improves reliability of flight software by reducing a complexity of the flight software. Korea Aerospace Research Institute chooses one of hypervisors for space, XtratuM, and examine its applicability to the flight software. XtratuM has strong points in performance improvement with high reliability. However, it does not support SMP. Therefore, it has limitation in using it with high performance applications including satellite altitude orbit control systems. This paper proposes RTEMS XM-SMP to support SMP with RTEMS, one of real time operating systems for space. Several components are added as hypercalls, and initialization processes are modified to use several processors with inter processors communication routines. In addition, all components related to processors are updated including context switch and interrupts. The effectiveness of the developed RTEMS XM-SMP is demonstrated with a GR740 board by executing SMP benchmark functions. Performance improvements are reviewed to check the effectiveness of SMP operations.

• Neonatal Medicine
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• v.18 no.1
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• pp.76-81
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• 2011

Purpose: The object of this study was to evaluate the efficacy of early total parenteral nutrition with early amino acid in extremely low birth weight infant (ELBWI). Methods: We retrospectively analyzed the medical records of all ELBWIs who were born and admitted to Samsung Medical Center from January 2003 to December 2003 and January 2009 to December 2009 and alive at the time of discharge. Data for nutritional status and morbidities were compared between period 1 (2003, n=22), in which parenteral nutritional support was started gradually over several days and period 2 (2009, n=38), in which parenteral nutrition with amino acid was started as soon as possible after birth. Results: Compared to period 1, birth weight and Apgar score were lower in period 2. The intake amount of glucose, amino acid and total calorie was higher and the level of blood urea nitrogen was increased more from 7th day to 14th day after birth in period 2 when compared than period 1. The weight gain velocity was faster at 7th and 14th postnatal day in period 2. There were no differences in the incidence of necrotizing enterocolitis, moderate to severe bronchopulmonary dysplasia, and severe intraventricular hemorrhage (${\geq}$ Gr III) between two periods but, the incidence of periventricular leukomalacia(PVL) was significantly lower in period 2. Conclusion: Early initiation of total parenteral nutrition with early amino acid in ELBWIs was beneficial at weight gain with lowering catabolism and increasing anabolism. And it could be related with reducing the incidence of PVL.