TMS320F28388S: CAN FD issues

Hi,

Our expert will get back ASAP.

Thanks,

Saravanan

 Haim,

                If everything works fine at 2 Mbps but you get errors at 4 Mbps, it likely points to a timing issue. Points to ponder:

• Capture a transmitted frame from both the transmitter and the receiver and verify the bit-time is exactly according to the calculations.
• What is the clock source used for the 28388S? Is it an external quartz crystal or a quartz oscillator?
• Please check out the debug tips in www.ti.com/lit/SPRACU9.pdf.

hi Hareesh,

I have connected the TX and the Rx to the scope and got the following data: Data bit time is 250 ns (exactly 1/4Mhz), delta between tx an rx is ~120 ns:

relevant registers:

DBTP :

TDC =1

DBRP=0

DTSEG1=20

DTSEG2=9

TDCR.TDCO=6

 PSR.TDCV = 24   --> from this 24 value i got that the transmitter delay is 24*Tq - Tq is CAN.Fclk (126Mhz) ==> 192 ns which is less that 250 so it should be ok 

please review these data and let me know if i am making a mistake or misunderstand something..

P.S. using an extern Master (Can Runner) as Tx manufacture and my program as Rx solely - it seems to work with no errors...

Thanks a lot

forgot to add - i also receive a lot of Error_Passive state flags - but i believe its derived from the main issue discussed   

You have not answered my question "What is the clock source used for the 28388S? Is it an external quartz crystal or a quartz oscillator?" 

Did you check out the debug tips in www.ti.com/lit/SPRACU9.pdf? 

It is interesting the MCU has no issues acting as a receiver @ 4 Mbps but is unable to transmit at that bit-rate. I hope you are aware that the values of DTSEG1 & DTSEG2 are increased by 1 when the MCAN module accesses it. Please answer all questions below: 

1. What is the clock speed of the device?
2. What is the input clock to the MCAN module?
3. Who is controlling the MCAN module? C28 or M4?
4. Can you please attach scope capture of the MCANTX pin?

answers for your questions:

16Mhz crystal --> we use the M4 core, to control the MCAN module, with clock of 124Mhz --> MCAN Clock is also 124Mhz

attached are the following printscreen:

first is the total transmitter message

second is the end part of the message

third is the start part of the message

legend: yellow is the TX and green is the RX 

frame: canid - 0x000000AB - Len is 8 , Data is : 0xBA AA AA AA AA AA AA AA

thanks

The value you write to DBTP register does not appear to be correct. It does not yield 4 Mbps exactly. Can you please take a screenshot of this register in CCS and send it?

I requested screenshot of the register, not your code. In other words, I'd like to know what gets actually written into the register.

attached print screen of the DTBP register - 0x00801490 

thanks

In one post, you say MCAN clock is 124 MHz, which yields a bit-rate of 3.875 Mbps.

In another post, you say MCAN clock is 126 MHz, which yields a bit-rate of 3.9375 Mbps. 

As you can see, neither values yield a bit-rate of exactly 4 Mbps.

the MCAN clock is 124Mhz - if I wrote 126 it was a mistake.

you are correct- so i changed the DTBP.DTSEG2 =8  this gives me the following equation: Mcan_clock/(1+(DTSEG2+1)+(DTSEG1+1)) * (DBRP+1)=

124M/(1+(8+1)+(20+1))*(0+1) =4M 

am i correct? 

do you use a different equation? if so can you explain your calculations?

thanks

inno said:

am i correct? 

Yes.

You have rejected the answer without explaining why. Please provide the reason.

I don't understand? which answer have i rejected? 

I have changed the value of the DTBP to fit the 4Mh - following the calculation - still not working (actually it gotten worse) 

I suggest we approach the problem from a different direction: 

can you tell me what are the values i need to set and in which registers - in order to get 4Mhz with 75% bus load?

thanks

inno said:

I don't understand? which answer have i rejected? 

I got an automated message that said you rejected my answer. It is no big deal. We can continue the discussion.

inno said:

I have changed the value of the DTBP to fit the 4Mh - following the calculation - still not working (actually it gotten worse) 

Please provide a screenshot of both NBTP and DBTP registers.

inno said:

can you tell me what are the values i need to set and in which registers - in order to get 4Mhz with 75% bus load?

For any given input clock, the bit-rate is solely determined by the NBTP and DBTP registers. The register values have no bearing on the bus load or vice versa. 

Can you please try SYSCONFIG to generate the register values?