Re: RE : [lwip-users] tcp_sent() question

[David Vos]

Thanks for the explanation.  I had read some old documentation
somewhere that suggested that lwip required you to handle resending
data yourself (the data due to lost packets).  Now I see why this
function is useful in other ways.

Thanks,
-David

On 7/29/07, Frédéric BERNON <address@hidden> wrote:
> Rawapi.txt said :
>
> "- void tcp_sent(struct tcp_pcb *pcb,
>                 err_t (* sent)(void *arg, struct tcp_pcb *tpcb,
>                        u16_t len))
>
>   Specifies the callback function that should be called when data has
>   successfully been received (i.e., acknowledged) by the remote
>   host. The len argument passed to the callback function gives the
>   amount bytes that was acknowledged by the last acknowledgment."
>
> What you have to understand is that tcp_sent enable to define your 
> "user-callback" function which will be called each time there is new "free 
> space" in your snd_buffer (most of time, you also have to defined tcp_arg). 
> You call use it to "resend" data or terminate any tcp operations.
>
> Most of time, for TCP "write" operations, you should check with tcp_sndbuf 
> the size available in the "tcp send buffer", and you have to send no more 
> than this size. You have to "loop" on that until all you block of data is 
> write (is "in the send buffer"). You could avoid to poll is there is any free 
> space in the "send buffer" by using tcp_sent callback: each time that any 
> space is available in the tcp send buffer, your user-callback will be called, 
> and you could retry to send datas... Like this, you replace you polling 
> (which can used some cycles) by a "event" features (which use "no" cycles). 
> Current CVS HEAD code for api_msg.c is a good sample for that. Take a look at 
> it...
>
> ====================================
> Frédéric BERNON
> HYMATOM SA
> Chef de projet informatique
> Microsoft Certified Professional
> Tél. : +33 (0)4-67-87-61-10
> Fax. : +33 (0)4-67-70-85-44
> Email : address@hidden
> Web Site : http://www.hymatom.fr
> ====================================
> P Avant d'imprimer, penser à l'environnement
>
>
>
> -----Message d'origine-----
> De : address@hidden [mailto:address@hidden De la part de David Vos
> Envoyé : dimanche 29 juillet 2007 03:58
> À : Mailing list for lwIP users
> Objet : [lwip-users] tcp_sent() question
>
>
> I'm confused what the purpose of the tcp_sent() function is.  Could someone 
> please explain it?
>
> Thanks,
> -David
>
>
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