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

Dinesh,

here is some VHDL code of a CAN core showing the filter process:

    -- Working in basic mode. ID match for standard format (11-bit ID).
    match <= (((((((CONV_STD_LOGIC(id(3)  = acceptance_code_0(0)) OR 
acceptance_mask_0(0))
               AND (CONV_STD_LOGIC(id(4)  = acceptance_code_0(1)) OR 
acceptance_mask_0(1)))
               AND (CONV_STD_LOGIC(id(5)  = acceptance_code_0(2)) OR 
acceptance_mask_0(2)))
               AND (CONV_STD_LOGIC(id(6)  = acceptance_code_0(3)) OR 
acceptance_mask_0(3)))
               AND (CONV_STD_LOGIC(id(7)  = acceptance_code_0(4)) OR 
acceptance_mask_0(4)))
               AND (CONV_STD_LOGIC(id(8)  = acceptance_code_0(5)) OR 
acceptance_mask_0(5)))
               AND (CONV_STD_LOGIC(id(9)  = acceptance_code_0(6)) OR 
acceptance_mask_0(6)))
               AND (CONV_STD_LOGIC(id(10) = acceptance_code_0(7)) OR 
acceptance_mask_0(7)) ;

The "=" operator means equivalence ...

--Armin


Dinesh Guleria wrote:
> 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] 
> <mailto:[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] <mailto:[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
>>>
>>>
>>
>
>