N_Cs timing - was Re: linux-can ISOTP module

[Oliver Hartkopp <socketcan@hartkopp.net>]

Hi Laurent,

as the extended address specification for the rx path is discussed/answered
in another thread I changed the subject for the timing discussion ...

On 05.06.2014 09:16, laurent vaudoit wrote:

> 
> Ok, with isotp.h api, i understand that we can parameter block size, stmin,
> wftmax, transmission time (n_ax), padding.
> But how can i specify the timing n_CS (time between flow control reception
> and first consecutive frame)

N_Cs is defined by the received STmin.

Then the tx_gap time is calculated by tx_gap = N_As + N_Cs

https://gitorious.org/linux-can/can-modules/source/027899c01aa2482423376e1e9f2a5875c316303a:net/can/isotp.c#L324

Finally the timer for the tx job is started relatively with this value
which leads to the required gap between the FC reception and the first CF. 


> and the timing n_BS (time between first frame
> reception and flow control emission)? 

N_Bs = N_Br + N_Ar

N_Ar is defined by the frame transmission time (on the real CAN bus)
N_Br has no setting but only a performance requirement:

N_Br + N_Ar < 0.9 * N_Bs timeout

N_Bs timeout = 1000ms => N_Br + N_Ar < 900ms

So AFAICS there's no way to specify N_Br. It can be as small as possible.
Therefore N_Bs is at least N_Ar + some various time for the protocol machine. 

> In the same way, is it possible to
> specify according timeout (n_BR for flow control timeout reception, and n_CR
> for consecutive frame timeout reception)?

Due to the spec all these timeouts are defined to be 1000ms.
Or did I miss something here?

Regards,
Oliver