Re: [lwip-users] Bug in pbuf.c regarding PBUF_POOL

[Christiaan Simons]

@Jonathan:

> > We have a proven real-time pre-emptive design (even with nested
> > pre-emptable interrupts) that does not use SYS_LIGHTWEIGHT_PROT but
uses
> > the "bottom-half" approach.
>
> I would be surprised if it were truly thread-safe given my understanding
of
> the current code. Maybe it used to be with different earlier code. But I
> haven't seen the code for that port.

What we do is truly thread safe,
since we protect the calls to the _raw-API_.

As Leon said the interrupt top half merely
wakes a high priority task (bottom half) on eth rx.

This task locks a (uCOS) mutex, copies data from the
ethernet controller and pushes this into the lwIP stack.
After lwIP is done we unlock this mutex.

Other tasks accessing to any lwIP structure
are allowed when the mutex is available.

We completely avoid the lwIP socket or sequential API,
therefore we don't require the troublesome lwIP
"protection".

Any finer grained locking would require
improved thread safety many places in the current
code as many observed correctly before.

BTW direct pbuf pool access is desirable
for raw-API applications, such as SNMP.

Christiaan Simons

Hardware Designer
Axon Digital Design

http://www.axon.tv

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