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<a href="https://gitlab.rtems.org/ppisa">Pavel Pisa</a>
<a href="https://gitlab.rtems.org/rtems/rtos/rtems-examples/-/merge_requests/22#note_147237">commented</a>:
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<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">For information, RTEMS CAN/CAN FD stack support use of single interface for multiple applications which can interact with other nodes connected through CAN controller and CAN bus but they can even interact in between on a given node. When the message is send successfully by the controller then it is echoed back to all other local open of the given controller. Echoing to the sending file object/handle is filtered by default, <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">CAN_FRAME_ECHO</code> mask is set on queues by default. But the <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">CAN_FRAME_LOCAL</code> to distribute locally sent frame to other local applications is enabled in the filters by default.</p>
<p dir="auto" style="color: #3a383f; margin: 0;" align="initial">Because virtual CAN "chip" has no connection to external bus, the use of <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">CAN_FRAME_LOCAL</code> frames is the only way how to communicate over it. For the drivers operating with real hardware, they can be used same way but the rule for CAN communication is that the frame is not considered sent successfully if it is not confirmed by at least one other physical node on the bus. So solo controller would newer send message and that is why it even does not distribute it to the local applications. Some controllers can support setting <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">CAN_CTRLMODE_PRESUME_ACK</code> mode. When this mode is set, then even physical controller does considered the frame as sent successfully even if no other node acknowledges it. In such cane, multiple applications can run on the single node with single controller and the communication can be observed on physical interface for example by oscilloscope.</p>
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