S32K344 FlexCAN Change Highest-priority message buffer first to Lowest-number message buffer first

[bruceyun]

Hi all, 

I am working on a project to route CAN messages. I found out that CAN write block by default has arbitration process, which choose highest-priority CAN message buffer to send first. I want to change it to lowest-number message buffer to send first. 

After I read document, there are some lines: 

73.3.3.1
Lowest-number message buffer first
"If CTRL1[LBUF] is 1, the first (lowest number) active transmission message buffer found is the arbitration winner. MCR[LPRIOEN] has no effect when CTRL1[LBUF] is 1."

So I am trying to write CTRL1[LBUF] to 1. I believe that I need to change to Freeze Mode. 

"MCR[FRZ] must be 1 and the module must not be in a low-power mode"

"After requesting Freeze mode, you must wait for MCR[FRZACK] to become 1 before executing any other action, otherwise FlexCAN may operate unpredictably. In Freeze mode, all memory-mapped registers are accessible."

I tried to write MCR[FRZ] to 1 but I failed to change to Freeze mode. Can anyone here have the knowledge about this? I appreciate it. 

##S32K34 #FlexCAN #CAN #Route #AUTOSAR #NXP

[SorinIBancila]

Hello,

To put the FLEXCAN module into FreezeMode, we can use the S32K3 RTD functions:

• FlexCAN_Ip_EnterFreezeMode_Privileged(uint8 instance)

• FlexCAN_Ip_ExitFreezeMode_Privileged(uint8 instance)

To test this I've added the following blocks to an already existing model that sends messages over CAN. Basically, I have a variable CAN_0_enterfreeze which I modify from the FreeMASTER to have one of the following values:

• 0: Do nothing
• 1: read MCR register for CAN 0 instance and store the result in CAN_0_MCR
• 2: Enter FreezeMode
• 3: Exit FreezeMode

Inside case 2 and case 3, you have to add a MATLAB function block. The custom code to enter/exit freezemode can be found below:

To validate this I've done the following:

• Reset the development board and read the content of MCR register for CAN 0 instance. 

• Set CAN_0_enterfreeze to 2 and read the content of the MCR register. Note! The FlexCAN is not working in FreezeMode.

 

•  Set CAN_0_enterfreeze to 3 and read the content of the MCR register. The CAN is working again. I just send a message (ID = 101) from CAN analyzer tool and the board replies with a message ID=0.

The S32K3 RTD sources can be found inside the toolbox, where you can check the implementation for a specific module in case you need it. To open the root of the S32K3 folder, you can type the following command in MATLAB command window : cd(mbd_find_s32k3_root). 

Do not hesitate to reply in case you have any other questions.

Best regards,

Sorin Bancila