Frame Input Stream Mode

NI-XNET 19.1 Help

Edition Date: June 2019

Part Number: 372841W-01

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This mode reads all frames received from the network using a single stream. It typically is used for analyzing and/or logging all frame traffic in the network.

The input data is returned as an array of frames. Because all frames are returned, your application must evaluate identification in each frame (such as a CAN identifier or FlexRay slot/cycle/channel) to interpret the frame payload data.

Previously, you could use only one Frame Input Stream session for a given interface. Now, multiple Frame Input Stream sessions can be open at the same time on CAN and LIN interfaces.

While using one or more Frame Input Stream sessions, you can use other sessions with different input modes. Received frames are copied to Frame Input Stream sessions in addition to any other applicable input session. For example, if you create a Frame Input Single-Point session for FrameA, then create a Frame Input Stream session, when FrameA is received, its data is returned from the call to nxReadFrame of both sessions. This duplication of incoming frames enables you to analyze overall traffic while running a higher level application that uses specific frame or signal data.

When used with a FlexRay interface, frames from both channels are returned. For example, if a frame is received in a static slot on both channel A and channel B, two frames are returned from nxReadFrame.

Example

In this example network, frame C is a cyclic frame that transmits on the network once every 2 ms. Frame E is an event-driven frame. For information about cyclic and event-driven frames, refer to Cyclic and Event Timing.

Each frame contains two signals, one in the first byte and another in the second byte.

The example uses CAN. The following figure shows a timeline of a frame transfer on the CAN network, followed by a single call to nxReadFrame. Each frame contains its name (C or E), followed by the value of its two signals.

The following figure shows the data returned from nxReadFrame.

Frame C and frame E are returned in a single array of frames. Each frame is displayed with CAN-specific elements. For information about the data returned from the read function, refer to Raw Frame Format. This example uses hexadecimal C and E as the identifier of each frame. The signal data is contained in the first two payload bytes. The timestamp represents the absolute time when the XNET interface received the frame (end of frame), accurate to microseconds.

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