TC1784
FlexRay™ Protocol Controller (E-Ray)
User´s Manual
20-197
V1.1, 2011-05
E-Ray, V3.13
•
Checked against limit values
•
Correction value is a signed integer number of Microticks
•
Distributed over Macroticks comprising the next
even / odd
cycle pair (Macroticks
lengthened / shortened)
Synchronization Process
Clock synchronization is performed by means of SYNC Frames. Only preconfigured
nodes (sync nodes) are allowed to send SYNC Frames. In a two-channel cluster a sync
node has to send its SYNC Frame on both channels.
For synchronization in FlexRay™ the following constraints have to be considered:
•
Max. one SYNC Frame per node in one communication cycle
•
Max. 15 SYNC Frames per cluster in one communication cycle
•
Every node has to use all available SYNC Frames for clock synchronization
•
Minimum of two sync nodes required for clock synchronization and startup
For clock synchronization the time difference between expected and observed arrival
time of SYNC Frames received during the static segment, valid on both channels (two-
channel cluster), is measured. The calculation of correction terms is done during network
idle time (NIT) (offset: every cycle, rate: odd cycle) by using a FTA / FTM algorithm. For
details see FlexRay™ protocol specification v2.1, chapter 8.
SYNC Frame Transmission
SYNC Frame transmission is only possible from buffer 0 and 1. Message Buffer 1 may
be used for SYNC Frame transmission in case that SYNC Frames should have different
payloads on the two channels. In this case bit
has to be programmed to 1.
Message Buffers used for SYNC Frame transmission have to be configured with the key
slot ID and can be (re)configured in “DEFAULT_CONFIG” or “CONFIG” state only. For
nodes transmitting SYNC Frames
must be set to 1.
20.6.3.4 External Clock Synchronization
During normal operation, independent clusters can drift significantly. If synchronous
operation across independent clusters is desired, external synchronization is necessary;
even though the nodes within each cluster are synchronized. This can be accomplished
with synchronous application of host-deduced rate and offset correction terms to the
clusters.
•
External offset / rate correction value is a signed integer
•
External offset / rate correction value is added to calculated offset / rate correction
value
•
Aggregated offset / rate correction term (ex internal) is not checked against
configured limits
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