Re: [lwip-users] Expected behavior of linkoutput()?

[Grant Edwards]

On 2022-01-12, Simon Goldschmidt <goldsimon@gmx.de> wrote:
> Am 12. Januar 2022 18:45:44 MEZ schrieb Grant Edwards 
> <grant.b.edwards@gmail.com>:
>>On 2022-01-12, Sylvain Rochet <gradator@gradator.net> wrote:
>>
>>> 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.
>>
>>So, when using an OS, I can assume that lwIP will never call
>>linkoutput() from a non-thread context or from a protected region?
>
> Yes.

Thanks. I'm _guessing_ that the authors of this "driver" chose not to
have a tx fifo/queue in order to reduce latency for the high-priority
real-time protocol packet transmissions. It also appears that the
Ethernet TX hardware doesn't support chained tx dma packet descriptors
the way all the other MACs I've ever seen did, so adding a tx
queue/fifo would have to be done entirely in software instead of
having a fixed set of tx descriptors linked in a ring as is usually
done.

--
Grant