Popular Science Series: Comparison of AUTOSAR and OSEK Network Management (Part 1)

1. Introduction

The fundamental purpose of automobile network management is to save power. The basic implementation method is that when the car is not in use, some ECUs will enter low-power mode or sleep mode through network management coordination, thereby achieving the purpose of saving power. There are currently two mainstream network management standards, one is AUTOSAR (Automotive Open System Architecture), and the other is OSEK. Although the network management methods of AUTOSAR and OSEK are different, it can be considered that AUTOSAR is developed based on OSEK/VDS.

So how do these two standards implement network management functions? What are the differences? What are the similarities?

2. OSEK and AUTOSAR Network Management Implementation Principle

OSEK Network Management

1. State Machine

The state transition of the OSEK network management state machine is multi-layered and has three main states:

Figure 1 OSEK network management main status diagram

NMOff: Network Management Off

NMOn: Network Management is running

NMShutDown: Shut down the network management operation. This process will clean up some data generated during the operation.

There are two sets of parallel sub-states in the NMOn state, which do not affect each other:

Figure 2 Schematic diagram of sub-states in NMOn state

NMInit: Mainly hardware initialization, this state is very short (initial)

NMAwake: Generally, the node maintains the state for a long time and performs normal network management

NMBusSleep: Sleep state, network management communication stops

NMActive: Participate in network management (initial)

NMPassive: The node does not participate in network management but still monitors network activity

There are also three sub-states in the NMAwake state:

Figure 3. Schematic diagram of sub-states in NMAwake state

NMReset: software initialization, sending alive message

NMNormal: Periodically sends or receives Ring messages to detect changes in node status and network configuration

NMLimpHome: The node is in an abnormal state and cannot send and receive network management messages normally. Try to send limp messages periodically.

The schematic diagram of a node's transition from sleep to wake-up and then to sleep is as follows:

Figure 4 OSEK network management status jump diagram

2. NM message format

The messages directly related to network management are network management messages. Network management messages can be divided into Alive messages, Ring messages, and LimpHome messages according to the different bit settings of byte 1 in the data they carry. Byte 1 of the network management message also carries information on whether each node meets the sleep condition, which are called SleepInd information and SleepACK information.

Alive message (bit 0 in byte 1 is set): a statement sent by each node when it needs to join the logical ring.

example:

Ring message (bit 1 in byte 1 is set): A network management message transmitted by a "token" in a logical ring.

example:

LimpHome message (bit 2 in byte 1 is set): a special message sent when the node is in an abnormal state and cannot send or receive network management messages.

example:

SleepInd information (bit 4 in byte 1 is set): data carried in the network management message operation code, indicating that the node that sends this information no longer actively requests network communication.

example:

SleepACK information (bit 4 and bit 5 in byte 1 are set): indicates that all nodes in the network no longer need network communication. After receiving the message of this information, all nodes stop communicating and enter sleep.

example:

3. Logical loop

Logical ring: The logic of network management message transmission. In a normal communication network, a node can only send out its own network management message after receiving the network management message sent by other nodes to itself, that is, the "token". Therefore, only one node in the network can send out a network management message at the same time. Each node sends the network management message in sequence. This sequence is called a logical ring. The schematic diagram is as follows:

Figure 5 Schematic diagram of logic loop

The "Token" is in NodeB, and NodeB sends a network management message to NodeC.

NodeB sends a network management message to NodeC, and the "Token" is transferred to NodeC.

The "Token" is in NodeC, and NodeC sends a network management message directed to NodeA.

NodeC sends a network management message to NodeA, and the "Token" is transferred to NodeA.

The "Token" is in NodeA, and NodeA sends a network management message to NodeB.

NodeA sends a network management message to NodeB, and the "Token" is transferred to NodeB.

AUTOSAR Network Management

1. State Machine

AUTOSAR network management has only three modes:

Figure 6 Schematic diagram of AUTOSAR network management mode

BusSleepMode: Bus sleep mode, the state when the controller with AUTOSAR network management function is in normal sleep mode.

PrepareBusSleepMode: Bus pre-sleep mode. This state is a transitional state in which nodes in the network stop communicating and prepare to enter sleep mode. They will not remain in this state for a long time.

NetworkMode: Network mode, the state when there is a communication request in the network.

There are three sub-states under NetworkMode. AUTOSAR network management determines whether nodes need to communicate based on these three sub-states:

Figure 7. Network Mode sub-state diagram

RepeatMessage State: Repeat message state. This state is not a long-term state. It enters this state when entering network mode from sleep mode or ready-to-sleep mode. It sends its own network management message so that other nodes in the network can detect it. It can also be used to detect currently online nodes.

NormalOperationState: Normal operation state, the state in which a node needs network communication and periodically sends its own network management messages.

ReadySleep State: Ready Sleep State, a state in which a node no longer needs network communication and no longer sends its own network management messages, but sends its own application messages normally.

All nodes in a normal communication network will maintain two states, one is NormalOperationState and the other is ReadySleepState. The difference between these two states is whether the network management message is sent or not.

The transition of a node from sleep to wake-up and then to sleep is as follows:

Figure 8 AUTOSAR network management state transition diagram

2. NM message format

Since AUTOSAR network management messages are broadcast and do not need to specify any node, the message only contains its own ID, a small amount of control information, called the control bit vector, and user data.

Figure 9 AUTOSAR network management message format

So far, this article has briefly introduced OSEK and AUTOSAR network management in terms of state machine and network management message format.

This article focuses on the comparison of the two network management characteristics. Due to the length limitation of the article, please refer to the article "Popular Science Series: Comparison of AUTOSAR and OSEK Network Management (Part 2)".

To be continued.