Pettinato, Jim wrote:
Leon et al, I agree completely... If you have a pre-emptive OS, the
interface need only signal it needs serviced; a high-priority task can
handle feeding packets into the stack. Without such a prioritized
platform though, performance would be severely degraded if handled any
other way than directly in the ISR.
I also agree that I wouldn't push a packet all the way up the stack
directly in the ISR...
Just in case, no-one so far has been suggesting passing the packet into the
stack from an ISR, but I think the rest of your mail shows you do know that :).
I'm not sure a high priority task is sufficient, if that task can block for
an indeterminate time waiting for a lower priority task (semaphores suffer
from priority inversion). So it really makes no difference whether it's
called from a high priority thread or a bottom half - we don't want to
block either way round.
If PBUF_POOL pbufs were only allocated from a single context (and different
bottom halfs would be sufficient for this, for example), this could all be
avoided; but they aren't. It's not clear to me why many of these calls are
from PBUF_POOL, rather than PBUF_RAM.
Incidentally, having to have a bunch of threads around to handle these
sorts of issues is a big waste due to the extra thread control blocks and
thread stacks - precious memory in the context in which lwIP is intended to
be used. Personally, I'm changing lwIP not to rely on such a model for
ethernet at least - for me it's a simple change in fact.
Jifl
--
eCosCentric http://www.eCosCentric.com/ The eCos and RedBoot experts
------["The best things in life aren't things."]------ Opinions==mine
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