[Xenomai-help] CAN question

[Xenomai-help] CAN question

[roland Tollenaar]

Hi,

In choosing listen_only or Loop_back. What am I actually selecting?
The documentation only tells me that the parameter sets loop_back or
listen_only mode. Not what the difference is between those modes.
Again one of those general network programming features I presume.

When working with the virtual device. Does it matter which mode is chosen?

Regards,

Roland

Re: [Xenomai-help] CAN question

[Jan Kiszka]

[-- Attachment #1: Type: text/plain, Size: 969 bytes --]

roland Tollenaar wrote:
> Hi,
> 
> In choosing listen_only or Loop_back. What am I actually selecting?
> The documentation only tells me that the parameter sets loop_back or
> listen_only mode. Not what the difference is between those modes.
> Again one of those general network programming features I presume.

Both modes affect the controller directly if it supports it. Listen-only
means that this CAN node will not acknowledge incoming frames even if
they are correct, it will just sit there and sniff passively.

Loopback means that the hardware emulates a fully working bus (i.e.
correctly terminated) with only one node that simply receives what it sends.

[Granted, documentation might be improvable here for CAN beginners.
Still, you need basic some CAN understanding to deal with real-life
issues anyway.]

> 
> When working with the virtual device. Does it matter which mode is chosen?

Nope, none of them is emulated so far.

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 250 bytes --]

Re: [Xenomai-help] CAN question

[roland Tollenaar]

Hi .

It sounds like I will be setting to listen_only in most practical
cases with a fully operational bus connected. Correct?

Thanks.

Roland



On 2/27/07, Jan Kiszka <jan.kiszka@domain.hid> wrote:
> roland Tollenaar wrote:
> > Hi,
> >
> > In choosing listen_only or Loop_back. What am I actually selecting?
> > The documentation only tells me that the parameter sets loop_back or
> > listen_only mode. Not what the difference is between those modes.
> > Again one of those general network programming features I presume.
>
> Both modes affect the controller directly if it supports it. Listen-only
> means that this CAN node will not acknowledge incoming frames even if
> they are correct, it will just sit there and sniff passively.
>
> Loopback means that the hardware emulates a fully working bus (i.e.
> correctly terminated) with only one node that simply receives what it sends.
>
> [Granted, documentation might be improvable here for CAN beginners.
> Still, you need basic some CAN understanding to deal with real-life
> issues anyway.]
>
> >
> > When working with the virtual device. Does it matter which mode is chosen?
>
> Nope, none of them is emulated so far.
>
> Jan
>
>
>

Re: [Xenomai-help] CAN question

[Jan Kiszka]

[-- Attachment #1: Type: text/plain, Size: 255 bytes --]

roland Tollenaar wrote:
> Hi .
> 
> It sounds like I will be setting to listen_only in most practical
> cases with a fully operational bus connected. Correct?

Err? What are practical cases for you?

Both modes are _debugging_ features.

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 250 bytes --]

Re: [Xenomai-help] CAN question

[Roland Tollenaar]

Hi Jan,

 >
 > Err? What are practical cases for you?
 >
 > Both modes are _debugging_ features.

Huh? There only seem to be two flavours. Listen_only or loopback. Are 
you saying that for normal operation it does not matter at all what the 
setting is? I.e. don't even have to bother setting the parameter?

Regards,

Roland.



Jan Kiszka wrote:
> roland Tollenaar wrote:
>> Hi .
>>
>> It sounds like I will be setting to listen_only in most practical
>> cases with a fully operational bus connected. Correct?
> 
> Err? What are practical cases for you?
> 
> Both modes are _debugging_ features.
> 
> Jan
> 

Re: [Xenomai-help] CAN question

[Jan Kiszka]

[-- Attachment #1: Type: text/plain, Size: 673 bytes --]

Roland Tollenaar wrote:
> Hi Jan,
> 
>>
>> Err? What are practical cases for you?
>>
>> Both modes are _debugging_ features.
> 
> Huh? There only seem to be two flavours. Listen_only or loopback. Are
> you saying that for normal operation it does not matter at all what the
> setting is? I.e. don't even have to bother setting the parameter?
> 

Check the documentation of SIOCSCANCTRLMODE. It should clearly state
that those are modes can be activated additionally and independently.
Also check what happens in the existing rtcanconfig code, it underlines
this.

If you find an even better way to express this in the doc: patches are
welcome.

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 250 bytes --]

Re: [Xenomai-help] CAN question

[Wolfgang Grandegger]

Jan Kiszka wrote:
> Roland Tollenaar wrote:
>> Hi Jan,
>>
>>> Err? What are practical cases for you?
>>>
>>> Both modes are _debugging_ features.
>> Huh? There only seem to be two flavours. Listen_only or loopback. Are
>> you saying that for normal operation it does not matter at all what the
>> setting is? I.e. don't even have to bother setting the parameter?
>>
> 
> Check the documentation of SIOCSCANCTRLMODE. It should clearly state
> that those are modes can be activated additionally and independently.
> Also check what happens in the existing rtcanconfig code, it underlines
> this.
> 
> If you find an even better way to express this in the doc: patches are
> welcome.

I'm going to update the doc as follows:

/*!
  * @anchor CAN_CTRLMODE @name CAN controller modes
  * Special CAN controllers modes, which can be or'ed together.
  *
  * @note These modes are hardware-dependent. Please consult the hardware
  * manual of the CAN controller for more detailed information.
  *
  * @{ */

/*! Listen-Only mode
  *
  *  In this mode the CAN controller would give no acknowledge to the
  *  CAN-bus, even if a message is received successfully and messages
  * would not be transmitted. This mode might be useful for
  * bus-monitoring, hot-plugging or throughput analysis. */
#define CAN_CTRLMODE_LISTENONLY 0x1

/*! Loopback mode
  *
  * In this mode the CAN controller does an internal loop-back, a message
  * is transmitted and simultaneously received. That mode can be used for
  * self test operation. */
#define CAN_CTRLMODE_LOOPBACK   0x2

Hope it's clearer now. For the moment, just don't care about special 
features.

Wolfgang.