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

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
>