REAL-TIME SYSTEMS II Real-Time Networking WorldFIP ... - EPFL

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Variable transfers Message transfers Real-Time Networks – WorldFIP 13 • the DLL associates • a buffer (B_DATprod) to each identifier of produced variable • a buffer (B_DATcons) to each identifier of consumed variable PRODUCER DLL BUS DLL CONSUMERS L_PUT.req L_PUT.cnf B_DAT prod ID B_DAT cons ID L_GET.req L_GET.cnf ©2010, J.-D. Decotignie SOURCE L_MESSAGE. request L_MESSAGE. confirmation Real-Time Networks – WorldFIP 14 • the DLL associates • a queue (F_MSG) for the messages it needs to send • a queue (F_MSGreçu) for the messages that it receives DLL F_MSG DLL F_MSG reçu DESTINATION L_MESSAGE. indication ©2010, J.-D. Decotignie Behavior Medium access control • variables Real-Time Networks – WorldFIP 15 • writing (reading) a variable does not trigger directly any traffic on the network • a new write operation overwrites the previous variable value • reception and emission of a value is signaled • → flow control possible (not necessary) • messages • stored in a queue → no overwrite • transfer is signaled → flow control • duplications are avoided using alternating bit protocol ©2010, J.-D. Decotignie Stage 1: BA broadcast identifier BA D D D D D Stage 3: producer broadcasts data BA D P D C C Real-Time Networks – WorldFIP 16 BA Stage 2: the producer and all consumers recognize the ID D P D C C Stage 4: all consumers acquire data BA D D D C C ©2010, J.-D. Decotignie
Bus Arbiter (BA) Signalling a request Real-Time Networks – WorldFIP 17 • control medium access • a single one is active, however several may be in backup • triggers all transactions • cyclic variable and message transfers • decided at configuration • configuration may be changed at run time • on-request variable and message transfers As a station may not emit without being invited to, each station must possess a mean to inform the Bus Arbiter that it requests a transfer ©2010, J.-D. Decotignie Real-Time Networks – WorldFIP 18 • uses the periodic transfer of variables • in its response to a periodic variable transfer invitation (from the Bus Arbiter), the producer DLL will indicate its request a station that does not produce any periodic variable cannot explicitly require the transfer of a variable or a message • ⇒ message transfers are related to a variable identifier • BA will later poll the requesting station to get the list of identifiers of the variables or messages for which a transfer is requested ©2010, J.-D. Decotignie Operating principle Read / write buffer services Real-Time Networks – WorldFIP 19 • according to configuration and explicit requests, the BA will establish a polling order periodic window (variables + messages) aperiodic window (variable exchanges) elementary poll cycle aperiodic window (message transfers) synchronization window • the duration of the elementary polling cycle • is often constant (sampled data systems) • cannot exceed the duration of the smallest polling period requested by the users at configuration ©2010, J.-D. Decotignie Real-Time Networks – WorldFIP 20 • L_PUT/GET.request(identifier, value) • L_PUT/GET.confirmation(identifier, status) • status gives the result: • result OK, unknown identifier, identifier invalidated by Network management, buffer access conflict, data length non compatible with buffer PRODUCER L_PUT.req L_PUT.cnf DLL B_DAT prod ID BUS DLL B_DAT cons ID CONSUMERS L_GET.req L_GET.cnf ©2010, J.-D. Decotignie
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Page 3: Optical physical layer Topology usi
Page 7 and 8: Specified explicit request (RQ_Inhi
Page 9 and 10: Frame Format Timers Real-Time Netwo
Page 11 and 12: Spatial consistency Temporal behavi
Page 13 and 14: Example (2) Response time analysis
Page 15: Summary References Real-Time Networ

REAL-TIME SYSTEMS II Real-Time Networking WorldFIP ... - EPFL

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