I am preparing to write some code for a master controller that communicates (via CANbus) with multiple nodes in a product. Each node monitors its own sensors (i.e. voltages, currents, fault flags, etc.) and can be started/stopped by the master controller. The master controller also sends the data to a display.
I am using an STM32H7B3I-EVAL board and using the STM32CubeIDE environment to write the code. I am trying to determine some good practices for writing this code, but I am inexperienced in CAN communication. I wanted to get people's opinions on the following high-level questions:
First of all, you need to invent an application tier CAN protocol unless you have one already. This isn't entirely trivial and requires some experience of CAN. Here you first of all need to take bus load in account, which in turn depends on the amounts of nodes and data allowed, as well as the baudrate. How to design this also depends on if it's a control system (hard realtime, milliseconds) or just some industrial sensor network (hundreds of milliseconds or seconds).
If we want to be constantly monitoring, should all the code for transmitting and receiving data be in a never-ending while loop?
Probably not. Regarding RX, depending on what CAN controller you have, there will at least be some manner of RX FIFO. Modern controllers also support dedicated "mailbox" slots for individual messages, which is more powerful and easier to work with. Your only requirement for never losing data is that you empty the FIFO at least as often as FIFO size times the time it takes to send the minimum package size (DLC=0). Unless your program is very busy, this is usually not a tough realtime deadline to meet.
Regarding TX, again it depends on the controller, but here it is usually sufficient to see that the previously send message has been send before attempting a new one. And unless you are really competing hard for bus access during a time of heavy bus load, this shouldn't be happening. Sensible CAN application protocols have some simple scheduling requirements such as "this gets sent after x ms in relation to that". Re-sending messages lost due to errors is handled by the controller hardware.
Is it better to transmit all data then receive all data, or transmit data when needed and have an interrupt for received messages?
TX and RX buffers work independently of each other. Also what you are saying doesn't really make sense, since CAN is semi-duplex and one node's TX is another node's RX.
What are the pros/cons in using an RXBUFFER vs RXFIFO?
Those terms are pretty much synonymous. I suppose they may have some special meaning given a specific CAN controller, but you don't mention one (STM32 have several, one old and really bad "bxCAN" and one newer which I don't know much about. And some stubbornly insist on the horrible solution of using external controllers, particularly the Arduino kids).
Anyway, it is better to have neither, using a CAN controller with mailboxes is the best option. Unless the amount of expected identifiers are more than you have mailbox slots - in that case you have to direct low priority messages to a RX FIFO and use mailbox slots for high priority messages.