2163212_en-US

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Subject: S32K1XX CANFD Tx arbitration start delay

Hello

We're developing CAN FD on S32K146 board, I have come confusions about the Tx arbitration start delay which do need your kind support.

1. Is it mandatory to configure the TASD bit in FlexCAN CTRL2 registor using non-zero value?

2. If it is mandatory, how to choose the TASD value? I review the Ref manual, but it does confuzed me. I will put my configuration here:

a. CAN_CLK is the same with SYS_CLK(80MHZ);

b. EPRESDIV = 1; EPROPSEG = 46; EPSEG1 = 15; EPSEG2 = 15; ERJW = 15; (NBT in arbitration phase is 80)

c. FPRESDIV = 1;FPROPSEG = 7; FPSEG1 = 7; FPSEG2 = 3; FRJW = 3; (NBT in data phase is 20)

according to the formula in ref manual(page 1933), I get the below value:

CPCBN = (fSYS/BITRATEN) = 80 * 2 = 160;

NMBEND = [(9 * 160) - 4]/2 = 718;

That's so big!!!

And TASD = 31 - [2 * (12+1) + 4]/160 = 31

that is unreasonable. So could some one please tell me whether my understanding is right? or how to set the TASD value?

Thanks a lot.

Re: Subject: S32K1XX CANFD Tx arbitration start delay

TDC is Transceiver delay compensation. but anyway, forget my question, I misunderstood the manual

Re: Subject: S32K1XX CANFD Tx arbitration start delay

Hi@fan1234

No, it depends on the following factors. If set to the maximum, when multiple mailboxes or nodes compete for the bus, setting a larger TASD will artificially reduce the sending priority of the mailbox.

• Peripheral-to-oscillator clock ratio
• CAN bit timing variables that determine the CAN bit rate
• Number of message buffers (MBs) in use by the matching and arbitration processes

For TDC question: if S32K1xx has no auto TDC but only fixed TDC

I don't understand what you mean about TDC, could you explain it in more detail?

Re: Subject: S32K1XX CANFD Tx arbitration start delay

Thank you for your reply. so, that means for CANFD frames, even the max TASD will be OK, right?
And as you mentioned TDC before, i want to confirm if S32K1xx has no auto TDC but only fixed TDC?

Re: Subject: S32K1XX CANFD Tx arbitration start delay

Hi@fan1234

I checked and found that this value is not mandatory to be configured as non-zero value, but it is recommended that users configure the register because it is very necessary in some working conditions, such as high bus load, timing constraints

I created an Excel spreadsheet for the calculation, which seems to be more convenient.

First, I want to point out that your calculation is correct, but you need to check whether you are using CAN FD or not.

If you are using non-FD frames, the result should be 24.8125.

For reference,

Re: Subject: S32K1XX CANFD Tx arbitration start delay

sorry, the question is about "CTRL2[TASD] (Tx Arbitration Start Delay)", not TDC, please check it .

Re: Subject: S32K1XX CANFD Tx arbitration start delay

Hi@fan1234

Sorry for the misunderstanding, let me take time check your question again.