TMS570LS1224: CAN mailbox configuration tradeoffs

Hello,

The CAN mailbox is used to define the message object and the ID mask. The CAN frame on CAN bus has many fields which are specified in message object: IDE (11-bit ID, or 29-bit ID), ID which also sets the message priority, DLC, Data bytes. Make sure two nodes will never send the same ID value at the same time. 

Any CAN node starts a transmission when it has detected an IDLE bus. Two or more nodes may start a message at the same time. The conflict or collision is resolved by the arbitration. Arbitration is performed bit-wise (bit by bit on the ID and the IDE bit, no other bits are used). The node with the highest priority (lower ID value) continues and lesser priority nodes stop sending and immediately turn into receivers. Note: The losing node “knows” the beginning of the other message. CAN arbitration is non-destructive. The losing nodes will attempt to re-transmit at the next idle bus time.

- What happens if multiple messages arrive at the same time in the same mailbox?

QJ> there is only one valid message on CAN bus at a time. 

- How does the TI SDK (canMessageNotification) handle multiple interrupts from multiple mailboxes?

QJ> The interrupt source is determined by the int1ID and int0ID in the interrupt register. The message object 1 has the highest priority, and last message object (for example 64) has the lowest priority. The interrupt service routine (ISR) resets the message object's IntPnd when reading the message. When intPnd is cleared, the interrupt register will point to the next pending object with a pending interrupt (interrupt pending x register).

- How big is the internal CAN node Queue (when a message will be deleted)?

QJ> LS1224 supports 64 mailboxes. The CAN module doesn't delete the received message in message RAM. But the received message object in message RAM may be overwritten by the new coming message.

. 

Hi QJ,

Thanks for your answer.

I'm familiar with the CAN protocol, but not with the TI SDK. (The TI SDK approach for HAL configuration is different from other manufacturers (NXP S32SDK, STM32 CubeMx, Nordic Semiconductor, etc))


I want to define my CAN message inside of my source code. Not inside halcogen.

Therefore, If I want to configure dynamically 1 mailbox for sending CAN message, I need to 

1. Update the mailbox ID with `canUpdateID()`
2. Update the mailbox DLC with ???
3. Send the information with `canTransmit()`

To my understanding, there's no API for changing the mailbox size in the SDK?
Does the mailbox adjust automatically?

Another approach to solving this problem would be to configure the CAN mailbox before calling canInit().
Can this be done with `can2GetConfigValue()`?