Re: [lwip-users] almost there.... need some assistance with callbacks... etc..

[Christiaan Simons]

On Thu, 2004-09-16 at 03:16, Eric Shufro wrote:
> How should the lwip dhcp timers and arp timer as well as others be
> initialized?
> 
> I understand from earlier postings that they cannot be called from different
> threads. So how is that done then? I cant suspend the tcpip thread for an
> OSTimeDelay() amount of time.... So any help there would be great.
> 

Many RTOSes (like uCOS) provide a way to call initialisation
code before any task switching (and interrupts) occurs.
(before OSStart())

If you keep all lwip code in one task there is no problem at all.

> Also, as far as Ethernet drivers go, when an interrupt occurs, the ISR
> should disable interrupts, post a semaphore and exit right? - the work
> should be done in a separate task?

The ISR should mask its own source only I guess.
Its a good idea to put all ethernet processing
in a task and pend for a small (and fast) interrupt handler.

Simply put _all_ lwip background functions like
the driver, arp / dhcp / tcp timers in one task,
and use a semaphore or mutex to give application
tasks access to the stack (PCB or other socket access).
You can unmask the ISR in this task after a succesfull
pend on the Ethernet semaphore.

> 
> So should I create a separate task in the OS that simply has a while loop to
> service the cs8900 interrupt service queue (ISQ) but pends for the semaphore
> before doing it, and when the interrupt occurs, wakes up due to the posted
> semaphore?

Beware! Handle the ISQ with care. Since you use an RTOS everything
should work just fine in this case. You should note that the
cs8900 can keep your task extremely busy on heavy network loads! 

> 
> Does that make any concurrency problems, since its yet another thread?

If you protect the lwip code with a semaphore or a mutex
it should work just fine. I would recommend the solution
above (one task for lwIP) for its simplicity.

Bye,

Christiaan Simons




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