Re: Re: CAN Mask & Filter setting at ---- software level

Armin,

>>Isn't it?

The real result must be:-----
 !( ( filter ^ messageID_Rx ) & mask );

Above equation is working for me very well many a time i have  used it ..

//Dinesh

On Mon, Dec 3, 2012 at 11:25 PM, Steinhoff <[email protected]> wrote:

>
> Well,
>
> that what the SJA1000 specification is showing by the "aceptance schemes"
> with the
> logical gates is not correct ... there seems to be a misinterpretation of
> the IEC gate symbol "=" :)
>
> The real result must be:
>
> result = NOT( filter XOR id ) OR mask;
>
> Isn't it?
>
> --Armin
>
>
> Steinhoff wrote:
>
>
> Dinesh.
>
> the result should be:
>
> result = ( filter XOR id ) OR mask;
>
> Acceptance happens  if all bits are set in result.
>
> Regards
>
> --Armin
>
> PS: SJA1000 spec / p. 45
>
> Dinesh Guleria wrote:
>
> Got the concept.
>
>  Now if i want DM to trigger for following types 0x01 & 0x33 :--
>
>  Type to be accepted :--
> 0x01;                // 0000 0001
> 0x33;                // 0011 0011
>
>  mask = 0xCD;   // 1100 1101                        -----> put 0 for
> diffrent bits ------ & ------ 1 for common bits
> filter = 0x01;      // 0000 0001                         ------>put 0 for
> dont care bits ------ & ------ SAME VALUE for common bits
>
>  result = ( ( filter ^ a_ ) & mask );
> if(!result)
> {
>      //accept
> }
>
>
>  This will Rx 0x001, 0x003, 0x011, 0x013, 0x021, 0x023, 0x031 and 0x033
> IDs.
>
>  Still in terms of CAN Rx workload for the processor, only 6 unwanted IDs
> out of a possible total 2032 CAN IDs (for 11 bit IDEs) to Rx may be of some
> reduced workload benefit.
>
>  We can put further filtering at the next level of software to accept
> message what we want.
>
>  BTW, weonly get 2032 and not 2048 11 bit CAN IDs because no IDs are
> allowed to have all 7 most significant bits set at the same time.
>
>  Regards,
> Dinesh
>
>
> On Sat, Dec 1, 2012 at 9:34 PM, Dinesh Guleria <[email protected]>wrote:
>
>> Hi,
>>
>>  I have enable my can controller to receive all messages & trying to
>> filtering messages it at software level.
>> I referred following link by Heikki
>> http://old.nabble.com/Setting-CAN-MASK---ID-registers-td14881913.html
>>
>>  Suppose i want to receive only ID_1 & ID_2.
>> But I was not able to get the desired result ID-0x03 is still passing the
>> software filter
>>
>>
>>  ID_1  =  0x01;       // 0000 0001
>> ID_2  =  0x33;       // 0011 0011
>> mask = 0x32;       // 0011 0010
>> filter =    0x01;       // 0000 0001
>>
>>  if  ----  messageID_Rx  =  0x03
>>
>>  ==========  CODE ======================
>>
>>  result = !( ( filter ^ messageID_Rx ) & mask );
>>
>>  if ( result )
>> {
>>       // ID accepted
>> }
>>
>>
>>  ====================================
>>
>>  Can someone on list help me to correct this. Or can suggest me where i
>> am getting wrong ?
>> Any reply will be appreciable.
>>
>>  Thanks & Regards,
>>
>>  Dinesh
>>
>
>
>
>