CAN Filter

[Erenburg.Evgeny]

I set on a slave

 CAN_FilterInitStructure.CAN_FilterNumber = 0;
 CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdMask;
 CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;
 CAN_FilterInitStructure.CAN_FilterIdHigh = 0x0000;
 CAN_FilterInitStructure.CAN_FilterIdLow = 0x0064; 
 CAN_FilterInitStructure.CAN_FilterMaskIdHigh = 0x0000;
 CAN_FilterInitStructure.CAN_FilterMaskIdLow = 0x00FF;
 CAN_FilterInitStructure.CAN_FilterFIFOAssignment = 0;
 CAN_FilterInitStructure.CAN_FilterActivation = ENABLE;
 CAN_FilterInit(&CAN_FilterInitStructure);

master sends

TxMessage.ExtId = (opcode << 8) | 0х64;

but the slave dosen't get the message. without mask and filter the slave gets the message.

how should I set the mask and filter?

[Erenburg.Evgeny]

any body? no one in the community knows how the CAN filter works in STM32?

[T J]

here you can see some bits are high in the mask ? only these bits are tested in the filter

//##-2- Configure the CAN1 Filter ###########################################
sFilterConfig.FilterNumber = 0;
sFilterConfig.FilterMode = CAN_FILTERMODE_IDMASK;
sFilterConfig.FilterScale = CAN_FILTERSCALE_32BIT;
sFilterConfig.FilterIdHigh = 0x400 << 5; //11-bit ID in top bits
sFilterConfig.FilterIdLow = 0x0000;
sFilterConfig.FilterMaskIdHigh = 0x600 << 5; // resolves as 0x0400 - 0x05FF
sFilterConfig.FilterMaskIdLow = 0x0000;
sFilterConfig.FilterFIFOAssignment = 0;
sFilterConfig.FilterActivation = ENABLE;
sFilterConfig.BankNumber = 0;

The Mask is 0x600 // only these two bits are tested

The Filter is 0x400 // in those two bits, A9 must be high and A10 must be low,

everything else is "dont care", we only care about the Masked bits.

so anything within 0x400- 0x5FF is accepted

[Erenburg.Evgeny]

I see. Thank you.

But in my case - if I want to accept the messages only for ID = 0xXX64 (XX - don't care) - my settings above seems to be valid. However I don't get any messages with the filter applied.

[T J]

can you see my mask bits are shifted up 5 bits ?

sFilterConfig.FilterIdHigh = 0x400 << 5; //11-bit ID in top bits

[Erenburg.Evgeny]

Ah... I see. The mask should be shifted. Thank you.

[Erenburg.Evgeny]

I just can't understand - why shift 5? It should be 3.

 Ah...I see. STDID is in High part of the register.

[Tesla DeLorean]

Depends on what you're matching, the top half of the diagram is the High and the bottom is the Low portion.

​

For the STDID you want to use the high filter with the pattern shifted left 5 bits.

​

Filters have been described on the forum multiple times over close to a decade. ​

[Erenburg.Evgeny]

Still can't get it working.

I want to get ID = 0x64 , the rest don't care

CAN_FilterInitStructure.CAN_FilterIdHigh = 0x0064 << 5; 
CAN_FilterInitStructure.CAN_FilterIdLow = 0x0000; 
CAN_FilterInitStructure.CAN_FilterMaskIdHigh = 0x00FF << 5; 
CAN_FilterInitStructure.CAN_FilterMaskIdLow = 0x0000; 

But when a master sends ID = 0x1164 I don't get it with the filter applied.

[T J]

is that an extended ID ? or std ID ?

is that address outside the address range ? 0x1164 << 5 overruns the 16bit value...

if you are using extended IDs, then <<3 is correct...

[Erenburg.Evgeny]

Thank you. That was my mistake. I have an extended ID.

So if I have an extended ID it should be this way?

 CAN_FilterInitStructure.CAN_FilterNumber = 0;
 CAN_FilterInitStructure.CAN_FilterMode = CAN_FilterMode_IdMask;
 CAN_FilterInitStructure.CAN_FilterScale = CAN_FilterScale_32bit;
 CAN_FilterInitStructure.CAN_FilterIdHigh = 0x0000; 
 CAN_FilterInitStructure.CAN_FilterIdLow = 0x0064 << 3; CAN_FilterInitStructure.CAN_FilterMaskIdHigh = 0x0000; 
 CAN_FilterInitStructure.CAN_FilterMaskIdLow = 0x00FF << 3; 
 CAN_FilterInitStructure.CAN_FilterFIFOAssignment = 0;
 CAN_FilterInitStructure.CAN_FilterActivation = ENABLE;
 CAN_FilterInit(&CAN_FilterInitStructure);