Re: [Xenomai] Modified rtcan_virt driver

[Jan Kiszka <jan.kiszka@web.de>]

On 2012-10-04 15:26, Gilles Chanteperdrix wrote:
> On 10/04/2012 02:58 PM, Thierry Bultel wrote:
>> Le 04/10/2012 14:36, Gilles Chanteperdrix a écrit :
>>> On 10/04/2012 02:15 PM, Thierry Bultel wrote:
>>>> Hi,
>>>>
>>>> The existing rtcan_virt driver simulates a single CAN bus, on which are
>>>> N devices.
>>>> Sending to one dispatches the frame to all the others but the not to the
>>>> sender.
>>>>
>>>> This has several disadvantages:
>>>>
>>>> - First, to run an application that uses 2 or more physical buses, it
>>>> does not fit, because both devices would be linked together.
>>>> - Second, having N instantiated virtual devices is in some cases not
>>>> necessary, because an application can open the
>>>> same device several times, and simulate many CAN nodes, on that single
>>>> device.
>>>>
>>>> Thus I have written another rtcan_virt driver, based on the original one.
>>>>
>>>> Its behavior is as follows:
>>>>
>>>> - It instantiates N rtcan devices, that are independent (no frame from
>>>> one to another)
>>>> - Each virtual rtcan (rtcan0, rtcan1 ...) device has a matching peer
>>>> (rtcan0s, rtcan1s ...)
>>>> ('s' like 'slave' but I am opened to any other naming) another to
>>>> communicate with.
>>>> That 'slave' device isautomatically created.
>>>> I say 'slave' in quotes because the word hides the symmetrical aspect,
>>>> so it is likely unappropriate..
>>>>
>>>> It is today fully tested, my question was if it could be of interest for
>>>> the Xenomai mainline.
>>>> If Yes:
>>>> - some questions come, to my mind the most important one is if is a new
>>>> driver, or a patch for the existing one,
>>>> to modify its behavior depending on a parameter. If it is a new one,
>>>> what would be the appropriate name ?
>>>> - I would be happy to make it as a patch (not ready for that yet, and
>>>> until the first questions are answered)
>>>>
>>>> If No, I just apologize for the noise.
>>> I think it is interesting, what about linking the odd ones to the even
>>> ones for the symetry?
>>>
>> I have been thinking about it, but that would break a 'I do not modify 
>> my application' rule.
>> In my special case, the app uses buses "0" and "1", that the CanFestival 
>> stack translates to "rtcan0" and "rtcan1"
>>
>> It is Ok to have the "emulated remote nodes" configured to use whatever 
>> "rtcan" name,
>> but from the application point of view it should be transparent.
> 
> Ok, then, what about adding an "nr_devs" parameter to rtcan_virt, and
> linking device #n with device #n + nr_devs for n between 0 and nr_devs - 1 ?
> 

You could make 'devices' an array and create a bus for each non-zero
array entry. Like with the number of virtual devices, this will just
require an upper limit of buses.

Jan

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