ISO 20794-2:2020 pdf download – Road vehicles — Clock extension peripheral interface (CXPI) — Part 2: Application layer.
5 Conventions This document is based on the conventions discussed in the OSI Service Conventions as specified in ISO/IEC 10731. 6 Introduction to application and application layer 6.1 Application properties The application has the following properties: — communication methods; — message types; — network management (optional wake-up, sleep); — state management (state machine); — measurement and/or control data; and — error handling. 6.2 Application layer properties The application layer has the following properties: — message exchange; — message structure; and — service interface and parameters. 6.3 Message transmission A message consists of a request field and a response field. The node that corresponds to a request identifier composed in the request field can transmit the response field. 6.4 Communication methods Two communication methods are supported: — Event-triggered method Each node can request a request protected identifier field and response field based on an internal event occurrence.— Polling method The master node requests a request protected type identifier field (event request in polling method) to the lower OSI layers and then each node can transmit a request protected identifier field. The node corresponding to the request protected identifier field transmits the response field. 6.5 Message types The application layer supports the following message types: — request message field; — response message field; and — request sleep message field. 6.6 Error handling The error handling is based on the following measures: — CXPI network errors; and — sequence count error (optional). 7 Service interface parameters (SIP) 7.1 SIP — General The following subclauses specify the service interface parameters and data types, which are used by the application and application layer services. 7.2? SIP? —? Data? type? definitions This requirement specifies the data type definitions of the CXPI service interface parameters.
9.2.3 APP — Polling method There are two kinds of requests that the master node requests about the request protected identifier field and the request protected type identifier field. When the master node requests the request protected type identifier field (event request in polling method) to the lower OSI layers, each node can request the request protected identifier field. If multiple nodes request the request protected identifier field at the same time and the request protected identifier fields collide on CXPI network, a non-destructive arbitration takes place in the data link layer and the higher priority request protected identifier field is transmitted to the CXPI network. The node corresponding to the request protected identifier field requests the response field (PDU). The slave node only requests PDUs when it receives the request protection identifier field or request protected type identifier field from the master node. The slave node cannot request PDUs voluntarily.