RE : [lwip-users] Example port for a beginner

[Frédéric BERNON]

>That's not exactly true... 
I suppose that Mumtaz talk to a "full" api layer, even without api_msg.c & 
tcpip.c, so, I think in this case, it''s right

>If you want to know more about timeouts:  
It's a good explain, I think it will be good to copy/paste it in sys_arch.txt 
and sys.c...
  
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Frédéric BERNON 
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-----Message d'origine-----
De : address@hidden [mailto:address@hidden De la part de Goldschmidt Simon
Envoyé : mercredi 23 mai 2007 10:47
À : Mailing list for lwIP users
Objet : RE: [lwip-users] Example port for a beginner


> 4    Yes sys_timeouts  is pretty confusing but if you implement your
own api layer then you can ignore it all together 

That's not exactly true: if NO_SYS=0, you
a) have to supply a function in sys_arch.c (if NO_SYS=0) that returns a pointer 
to a list of timeouts that is unique for the current thread
B) have to make sure the value returned by sys_arch_mbox_wait() (and
sys_arch_sem_wait()) is correct (the number of miliseconds waited for a 
message)!

If you want to know more about timeouts: it is a linked list including function 
pointers and values of miliseconds to wait before calling the function. When 
waiting for a message in an mbox, the time waited is substracted from the first 
timeout, and if that time is 0, the timeout function is called and the first 
item is popped off the list. This mechanism only works if NO_SYS=0 since 
otherwise, you don't have mboxes. But if you have mboxes, you kind of get the 
timeout functionality for free. The downside of this approach is that the 
timing is pretty inaccurate. If you have many messages in the mbox and you will 
not have to wait on any message, sys_arch_mbox_wait() will always return 0 
since it didn't have to wait for the message. That way timeouts will not be 
called. Another bad example are some ports that always return 1 when waiting 
for a message and 0 if a message was available right away. That of course leads 
to totally inaccurate timeouts.


Simon


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