Other Parts Discussed in Thread: TCAN4550
I am using the TCAN4550-Q1 and some features do not appear to be explained in the documentation. There are some also notes in comments in the sample code that I don't find in the documentation. Here are my questions. If you can answer them and also tell me where I might find documentation that answers them, that would be very helpful.
1. I'm trying to understand the Timestamp counter. The sample code (in sllc469b.zip) sets TSCC to use the external time stamp value. It says "This is required to use time stamps with CAN FD". Where is this mode documented? What happens if I configure FD for internal timestamps? What is the timestamp count frequency in this case? Does this mean I need to supply an external clock somehere, or is some other hardware change needed? Some places in the documentation talk about CAN bit times. For FD, is this the nominal bit time or the data bit time, or does the time base actually vary when the bit time switches? How can I know what units of time the FD packet timestamps represent?
2. The sample code tries to set the CCR register several times. Is setting this register not reliable? Why not?
3. I need to be able to set many different data rates. I can calculate the period, but what is the best way to calculate the NominalTqAfterSamplePoint and DataTqAfterSamplePoint. The code examples for a nominal period of 40 sets Tq after sample point to 8, but for the data period of 20, it sets Tq after sample point to 5. It looks like maybe setting it to Period/4 or Period/5 would work, but what is the best setting?
4. I can get all the nominal and data rates I need setting the prescaler to 1. Is there any good reason to set it to a larger value?
5. The GFC register documents RRFE and RRFS bit, but the sample code has these lines:
gfc.RRFE = 1; // Reject remote frames (TCAN4x5x doesn't support this)
gfc.RRFS = 1; // Reject remote frames (TCAN4x5x doesn't support this)
Is it true that this is not supported even though it is documented in the data sheet? Why does the sample code set these bits?