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Grundlagen FlexRay BasicsV 1.1 22 2.6 Wakeup The transition from the low power state to a powered state of the Bus Drivers is called Wakeup. This transition can be initialized by the Communication Controller, or by the bus itself, if the Bus Driver receives Wakeup Patterns. For the latter, the Bus Driver has to identify at least two Wakeup Symbols. Not every ECU on a network is allowed to send Wakeup Patterns. If a ECU has the permission to send such patterns, it is called a Wakeup Node, and may send 2 to 63 Wakeup Symbols. A Wakeup Symbol is defined (see Figure 2.17) as a Data_0 phase followed by an Idle phase. To ensure the Bus Driver can identify these phases, the following timing constraints have to be obeyed: dWU 01 , dWU Idle1 , dWU 02 , dWU Idle2 > 4µs und dWU < 48µs. Figure 2.17 Wakeup Pattern [EPLS06] A network may only contain up to 3 Wakeup Nodes, since an overlap of several Wakeup Patterns could prevent a correct detection, see Table 2.2. Table 2.2 Wakeup Pattern Detection [EPLS06] Name Description Min Max Unit dWU 0Detect Acceptable limits for detecting a 1 4 µs Data_0 phase. dWU IdleDetect Acceptable limits for detecting an 1 4 µs Idle phase. dWU Timeout Acceptable limits for detecting a Wakeup Pattern 48 140 µs However, it is possible to define different Wakeup Nodes for channels A and B. This opens up additional possibilities for the network designer, as seen in the example in Figure 2.18. Here, the network on channel A is woken up by ECU1 due to a local event, while channel B is still asleep. Bäurle 12.10.2012
Grundlagen FlexRay BasicsV 1.1 23 Figure 2.18 Example of a wakeup After completing the Wakeup Phase, the Coldstart Nodes try to establish a communication on the bus, 2.7 Startup While starting up a FlexRay network, all timers of the ECUs are synchronized. The difficulty consists of synchronizing nodes with the communication, while not disrupting nodes which are already synchronized. This is examined in-depth in section 2.8. There are several scenarios which can occur during the Startup of a FlexRay network. It has to be considered that only Coldstart Nodes are allowed to send Startup Frames. Also, the ECUs have to be in POC:ready state, before they can participate in the Startup of the cluster. 1. Scenario – no Coldstart Node in the cluster This scenario occurs, if no Coldstart Node has been defined in the cluster, or if these nodes aren’t in POC:ready state. In practical use, this situation often occurs while testing a single ECU. For starting the communication in that case, the software has to simulate the Coldstart Nodes. Bäurle 12.10.2012
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