RE: CAN-BCM periodic send signaling

["Boris Baskevitch" <boris.baskevitch@annecy-elec.fr>]

Hi Oliver,

You're right, the frame counter is not incremented but it is reset.
In my case this results to showing only frame[0] of the bus as the payload
is updated more frequently than the message period.
I changed my updating function to let it change the 16 frames of the
message, but it's still not working:
I see no way to update a message frame without touching one byte (the last
one in my case) of the frame (to keep the frame counter untouched).
Reading the bcm.c source code, it uses the following memcopy command which
overwrite the whole frame.
http://lxr.free-electrons.com/source/net/can/bcm.c#L861

Boris


> -----Message d'origine-----
> De : Oliver Hartkopp [mailto:socketcan@hartkopp.net]
> Envoyé : mardi 7 janvier 2014 13:19
> À : Boris Baskevitch
> Cc : linux-can@vger.kernel.org
> Objet : Re: CAN-BCM periodic send signaling
> 
> 
> 
> On 07.01.2014 10:47, Oliver Hartkopp wrote:
> > Hi Boris,
> >
> > when you update the tx job please make sure that the nframes remains 16
> and
> > the entire message to the BCM contains 16 CAN frames.
> >
> > In your example below you switch back to a tx job with one single CAN
> frame
> > (== no sequence of 16 frames).
> >
> > Updating a BCM tx job content is just about copying the CAN frame
contents:
> > http://lxr.free-electrons.com/source/net/can/bcm.c#L847
> >
> > When you send only one frame in the updated tx job only this frame is
> copied
> > and the new nframes (==1) is taken for the job. Bye bye message sequence
> :-)
> >
> > http://lxr.free-electrons.com/source/net/can/bcm.c#L847
> 
> Typo:
> http://lxr.free-electrons.com/source/net/can/bcm.c#L938
> 
> >
> > Regards,
> > Oliver
> >
> > On 07.01.2014 09:29, Boris Baskevitch wrote:
> >> Hi Oliver,
> >> Thanks for the reply, the counter works well this way.
> >> But I also need to update the message with real payload in the other
bytes
> of the message.
> >> I placed the counter in the last byte of the message, I setup the
periodic
> message as you described (I extended it to a 4-bit counter, using 16
frames).
> >> Then I use the following function to update the payload without
touching
> the frame counter.
> >> This function if called much more frequently than the message period, I
> don’t use TX_ANNOUNCE in it to make sure the message period is stable on
> the bus.
> >> Unfortunately, doing this way is corrupting the frame counter: it seems
> that calling the update function is incrementing the frame pointer of the
> message.
> >> Note that when I update the payload, I update only msg.frame[0] and not
> the 15 other frames of the message, but on the bus, I can see that all the
> frames are updated with my payload. That's why I think the frame pointer
is
> updated each time I call the update function.
> >> Is there a way to update the payload without touching the frame pointer
?
> >>
> >> void UpdatePeriodicSendValues(void)
> >> {
> >>      struct {
> >> 	struct bcm_msg_head msg_head;
> >> 	struct can_frame frame[1];
> >>      } msg;
> >>
> >>     msg.msg_head.opcode = TX_SETUP;
> >>     msg.msg_head.flags = TX_CP_CAN_ID;
> >>     msg.msg_head.count = 0;
> >>     msg.msg_head.can_id = 0x42;
> >>     msg.msg_head.nframes = 1;
> >>     msg.frame[0].can_dlc = 8;
> >>
> >>     msg.frame[0].data[0] = MyData1 ;
> >>     msg.frame[0].data[1] = MyData2;
> >>     msg.frame[0].data[2] = 0;
> >>     msg.frame[0].data[3] = 0;
> >>     msg.frame[0].data[4] = 0;
> >>     msg.frame[0].data[5] = 0;
> >>     msg.frame[0].data[6] = 0;
> >>     //msg.frame[0].data[7] = this is the frame counter, don't touch it
!
> >>
> >>     write(m_fd, &msg, sizeof(msg));
> >>
> >>     return;
> >> }
> >>
> >>
> >>
> >> Boris
> >>
> >>
> >>
> >>> -----Message d'origine-----
> >>> De : Oliver Hartkopp [mailto:socketcan@hartkopp.net]
> >>> Envoyé : lundi 6 janvier 2014 19:09
> >>> À : Boris Baskevitch
> >>> Cc : linux-can@vger.kernel.org
> >>> Objet : Re: CAN-BCM periodic send signaling
> >>>
> >>> Hey Boris,
> >>>
> >>> On 06.01.2014 18:11, Boris Baskevitch wrote:
> >>>
> >>>> I'm using the CAN-BCM to send periodic CAN messages on the bus.
> >>>> In one of those messages, I need to send a counter value which is
> >>> incremented each time the message is sent.
> >>>> How can I do that ?
> >>>
> >>> E.g. if you have a 4 bit counter, you just send 16 "struct can_frames"
at
> >>> TX_SETUP time - also set nframes to 16 then.
> >>>
> >>> When nframes > 1 a sequence of CAN frames is sent automatically.
> >>> You may alter these CAN frames at runtime.
> >>> If you do so, the tx index may be set to "0" (start) with
> TX_RESET_MULTI_IDX.
> >>>
> >>> See tst-bcm-cycle.c from the
git://gitorious.org/linux-can/can-tests.git
> >>>
> >>> Here's the patch to demonstrate it based on can-tests repository with
> >>> nframes=4:
> >>>
> >>> diff --git a/tst-bcm-cycle.c b/tst-bcm-cycle.c
> >>> index b85ceed..adb2fd6 100644
> >>> --- a/tst-bcm-cycle.c
> >>> +++ b/tst-bcm-cycle.c
> >>> @@ -89,16 +89,29 @@ int main(int argc, char **argv)
> >>>
> >>>  	msg.msg_head.opcode  = TX_SETUP;
> >>>  	msg.msg_head.can_id  = 0x42;
> >>> -	msg.msg_head.flags   = SETTIMER|STARTTIMER;
> >>> -	msg.msg_head.nframes = 1;
> >>> -	msg.msg_head.count = 10;
> >>> -	msg.msg_head.ival1.tv_sec = 1;
> >>> +	msg.msg_head.flags   = SETTIMER|STARTTIMER|TX_CP_CAN_ID;
> >>> +	msg.msg_head.nframes = 4;
> >>> +	msg.msg_head.count = 0;
> >>> +	msg.msg_head.ival1.tv_sec = 0;
> >>>  	msg.msg_head.ival1.tv_usec = 0;
> >>>  	msg.msg_head.ival2.tv_sec = 0;
> >>> -	msg.msg_head.ival2.tv_usec = 0;
> >>> -	msg.frame[0].can_id    = 0x42;
> >>> +	msg.msg_head.ival2.tv_usec = 200000;
> >>> +
> >>> +	//msg.frame[0].can_id    = 0x42; /* obsolete due to TX_CP_CAN_ID */
> >>>  	msg.frame[0].can_dlc   = 8;
> >>> -	U64_DATA(&msg.frame[0]) = (__u64) 0xdeadbeefdeadbeefULL;
> >>> +	U64_DATA(&msg.frame[0]) = (__u64) 0x01000000deadbeefULL;
> >>> +
> >>> +	//msg.frame[1].can_id    = 0x42; /* obsolete due to TX_CP_CAN_ID */
> >>> +	msg.frame[1].can_dlc   = 8;
> >>> +	U64_DATA(&msg.frame[1]) = (__u64) 0x02000000deadbeefULL;
> >>> +
> >>> +	//msg.frame[2].can_id    = 0x42; /* obsolete due to TX_CP_CAN_ID */
> >>> +	msg.frame[2].can_dlc   = 8;
> >>> +	U64_DATA(&msg.frame[2]) = (__u64) 0x03000000deadbeefULL;
> >>> +
> >>> +	//msg.frame[3].can_id    = 0x42; /* obsolete due to TX_CP_CAN_ID */
> >>> +	msg.frame[3].can_dlc   = 8;
> >>> +	U64_DATA(&msg.frame[3]) = (__u64) 0x04000000deadbeefULL;
> >>>
> >>>  	if (write(s, &msg, sizeof(msg)) < 0)
> >>>  		perror("write");
> >>>
> >>> Does this fit your needs?
> >>>
> >>> Regards,
> >>> Oliver
> >>
> >>
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