Hi, On Wed, Jan 12, 2022 at 04:39:30PM -0000, Grant Edwards wrote: > What is the expected behavior of the netif linkoutput() function? > > Specificallyy, is it expected to > > 1) Block until the packet has been sent? > > or > > 2) Place the packet in a TX queue/fifo and return immediately? > > All of the Ethernet drivers I've worked on for other RTOSes in the > past couple decades expected 2), since the output function might be > called from a context that can not block. If the tx fifo/queue was > full, an error was returned. In either case the output function always > returned immediately. > > I'm currently looking at a blob of code that acts both as an Ethernet > driver for lwIP as well as implements a set of industrial protocols > "under the covers" without lwIP being aware of that traffic. The plan > is to remove the industrial protocl stuff and convert it into a > "normal" lwIP driver. > > That blob of code does 1) above. There is no TX packet queue/fifo at > all. the linkoutput() function copies the frame into the MAC, starts > transmission, and then blocks until transmission is complete. That > means that linkoutput must always be called from a normal OS thread > context. > > Is this blocking, non-queueing approach the normal way implement > linkoutput() for lwIP?
Actually, it should do both. Place the packet in the TX queue and return immediately, BUT if the queue is full it should wait for a free slot. Sylvain
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