magistrsko delo
Jaka Koren (Author), Branko Šter (Mentor), Rok Vogrin (Co-mentor)

Abstract

Vgrajeni sistemi so računalniške naprave, namensko oblikovane za izvajanje specifičnih nalog znotraj večjega sistema. Poseben problem pri takih sistemih je časovna usklajenost posameznih komponent; različne ure nihajo z različnimi frekvencami, kar povzroči neskladje med časovnimi oznakami podatkov, neoptimalno delovanje sistema in lahko tudi dejanske napake v programih. Za vzdrževanje dopustne časovne napake je treba to neskladje stalno popravljati. V okviru tega dela smo na razvojni platformi Beaglebone Black implementirali in preizkusili tri širše uporabljene metode za sinhronizacijo časa. Protokol za omrežni čas (NTP) je najstarejši in najbolj razširjen protokol na področju omrežne sinhronizacije ur, z velikim omrežjem internetnih strežnikov, ki nudijo referenčni čas. Odjemalci periodično povprašujejo strežnike v lokalnem omrežju ali na svetovnem spletu in preko algoritma za odmik izračunajo, kolikšen časovni popravek je treba dodati k lokalni sistemski uri. Protokol za natančni čas (PTP) lahko zagotavlja zelo visoko sinhronizacijsko točnost, če je strojna oprema naprav in povezav v omrežju ustrezno prilagojena. Namenjen je samo uporabi v lokalnih omrežjih, kjer lahko njegovi algoritmi za ocenjevanje odmika optimalno delujejo. Globalno satelitsko omrežje oz. Globalni sistem za pozicioniranje (GPS) poleg podatkov o lokaciji posreduje tudi podatke o času nekega položaja na Zemlji. Naprave, opremljene z GPS sprejemniki, lahko uravnavajo svoje ure po satelitskem času, pri čemer ne potrebujejo dostopa do internetnega omrežja, je pa ta metoda odvisna od kvalitete sprejema signalov z satelitov. Drugi programi na sistemu, konfiguracija omrežja in drugi dejavniki lahko vplivajo na kvaliteto sinhronizacije ter s tem usklajenosti programov med sistemi. V tem delu nas je predvsem zanimala slednja, zato smo za metode napisali lasten gonilnik, ki sproža signale ob določenem času glede na sistemsko uro. Preko meritev razlik med temi signali smo primerjali delovanje izbranih metod.

Keywords

vgrajeni sistemi;časovna sinhronizacija;omrežja;računalništvo in informatika;magisteriji;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FRI - Faculty of Computer and Information Science
Publisher: [J. Koren]
UDC: 004.3(043.2)
COBISS: 83604739 Link will open in a new window
Views: 250
Downloads: 42
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Other data

Secondary language: English
Secondary title: Global time in embedded systems
Secondary abstract: Embedded systems are dedicated micro-computers, designed to perform specific tasks within a larger system. Temporal synchronization of these devices within the system is an important issue; different clocks oscillate at different frequencies, creating offsets between time signatures of data packets, sub-optimal system operation and possible errors in programs. Time offsets between devices within the network must be constantly corrected to maintain a desirable accuracy. In this work, we have implemented three widely used time synchronization methods on the Beaglebone Black development platform. Network Time Protocol (NTP) is the oldest and most widely spread protocol for synchronization of network clocks, with a large global network of Internet servers for reference time access. Clients periodically query servers within a local network or on the Internet for time and using the synchronization algorithm apply a correction of time to the local system's clock. Precision Time Protocol (PTP) can ensure very high synchronization accuracy within the local network. With proper hardware and connections between devices, the clock offset can be reduced to below one microsecond. It can also automatically establish a hierarchy of clocks within a network and react to changes in the network structure, but does not support queries over the world wide web. Global Positioning System (GPS) transmits position and time data from a satellite network to receivers on Earth. Devices with such receivers can synchronize their clocks to GPS time, without having to be connected to a network. However, the quality of this method depends on the strength of the received satellite signal. Synchronization accuracy, as well as accuracy of programs that depend on system clock, can be also affected by configuration of the network, other running programs, and other factors. We were interested specifically in the offset between programs that trigger signals at specific time on separate devices. Selected methods are compared based on performance in tests using an example device driver dependent on system clock.
Secondary keywords: embedded systems;time synchronization;networks;computer science;computer and information science;master's degree;Vdelani računalniški sistemi;Računalništvo;Univerzitetna in visokošolska dela;
Type (COBISS): Master's thesis/paper
Study programme: 1000471
Thesis comment: Univ. v Ljubljani, Fak. za računalništvo in informatiko
Pages: 55 str.
ID: 13763252