Posted on March 21, 2017 at 10:57
Message ID encoding can be changed dynamically. The Node ID you're speaking of is a specific area that can be fixed by masking that area. Here's an example:
So the destination is something that I want to be fixed so the node's hardware will filter that out.
For initialization code:
/* USER CODE BEGIN CAN1_MspInit 1 */
canHandle->pRxMsg = &rx_msg;
canHandle->pTxMsg = &tx_msg;
canHandle->pTxMsg->IDE = CAN_ID_EXT;
// Filters
can_filter.FilterNumber = 0; // CAN 1 0..13
can_filter.FilterMode = CAN_FILTERMODE_IDMASK;
can_filter.FilterScale = CAN_FILTERSCALE_32BIT;
/*
* |- DEST 4bit -|- Origin 4bit -|- Frame Type 8bit -|- Count 5bit -|- EMPTY 8bit -|- IDE -| RTS -|- TXRQ -|
*/
can_filter.FilterIdHigh = 0x01; // ID 1 with IDE enabled
can_filter.FilterIdLow = CAN_F0R1_FB2;// 32bit register is based on 16 bit High << 16 | Low
/*
* Mask
*/
can_filter.FilterMaskIdHigh = 0xF00F;
can_filter.FilterMaskIdLow = CAN_F0R1_FB2;
can_filter.FilterFIFOAssignment = CAN_FIFO0;
can_filter.FilterActivation = ENABLE;
if(HAL_CAN_ConfigFilter(&hcan1, &can_filter) != HAL_OK)
{
Error_Handler();
}�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?�?The node ID is assigned on line ID = 0x01000008
But the mask starting on line 18 is where the magic happens. Mask = 0xF00F0008
Nerd translation is: ''You MUST match the first nibble from the ID, the 4th nibble of the ID, and the 3rd bit of the ID or else they won't pass the filter. Everything else.... I don't care''.
This will allow you to modify those bits that it doesn't care to modify dynamically like this:
// 2. Setup the Message ID encoding
hcan1.pTxMsg->ExtId =
( ( destination & 0x0F ) << ( 28 - EXTID_TX_OFFSET ) ) |
( ( CAN_HOST_ADDRESS & 0x0F ) << ( 24 - EXTID_TX_OFFSET ) ) |
( ( frame_type & 0xFF ) << ( 16 - EXTID_TX_OFFSET ) ) |
( ( frame_count & 0x1F ) << ( 11 - EXTID_TX_OFFSET ) );
�?�?�?�?�?�?Hope that was clear enough for you. Have fun.
