AM2634: On the TDCO configuration of the CAN secondary sampling points

Hi,

Can i understand that what is the sampling rate you needed?
And also are you using nominal baud rate or standard baud rate?

So that i can come back with the above questions.

Thanks,

Mudit Bhansali 

Hi,

1.The sampling point(SP) needs 80%

2.The second sampling point (SSP) also needs 80%

3.CAN FD data section baud rate needs 2M bps, arbitration section baud rate needs 500k 

Hi,

Can you check out our default configuration, i already have this right.

Thanks,

Mudit Bhansali

Hi，

The EB's default configuration is shown in Figure：

CanControllerFdBaudRate：5000

CanControllerPropSeg：2

CanControllerSeg1：2

CanControllerSeg2：3

CanControllerSyncJumpWidth：2

CanControllerTxBitRateSwitch ：Enable

CanControllerTrcvDelayCompensationOffset：180

1.You mean that the TDCO is 180 also fits the configuration?

CanControllerFdBaudRate：2000

CanControllerPropSeg：17

CanControllerSeg1：14

CanControllerSeg2：8

CanControllerSyncJumpWidth：8

CanControllerTxBitRateSwitch ：Enable

CanControllerTrcvDelayCompensationOffset：180

2.You mean TDCO is 180 fits SSP=80%, So is 100 or 400 right ?

3. Is there a calculation method for TDCO and SSP? For example, if SSP=80%, then TDCO= (CanControllerPropSeg+CanControllerSeg1+CanControllerSeg2+1) *80%. I want to know the relationship.

Thanks,

Xinlei Gu

Hi,

    CanConfigSet_CanController_0_CanControllerBaudrateConfig_0 =
{
    1000U,      /* in Kbps */
    20U,       /* Prop Segement value */
    14U,          /* Phase Segment 1 */
    5U,          /* Phase Segment 2 */
    1U, /* Sync jump width */
    40U, /* Sum of all timing parameters */
    2U,   /* Controller BRP value for Baud */
	 /* Data phase Baudrate */
    {
        5000U,     /* in Kbps */
        3U,        /* Prop Segement value */
        3U,           /* Phase Segment 1 */
        1U,           /* Phase Segment 2 */
        1U,  /* Sync jump width */
        8U, /* Sum of all timing parameters */
        2U,   /* Controller BRP value for Baud */
        14U, /* Specifies the Transceiver Delay Compensation Offset */
        (boolean)TRUE, /* Specifies if the bit rate switching shall be used */
    }
};

bit rate(bits per second) = (CAN clock in Hz) / BRP / (1 + TSEG1 + TSEG2)

where:

CAN clock is functional clock of CAN module (80MHz)

BRP: Bit rate pre-scalar value

TSEG1, TSEG2: Time segments used to define sampling point for the bit.

TSEG1: Time before the sampling point = Prop_Seg + Phase_Seg1

TSEG2: Time after the sampling point = Phase_Seg2

In this configuration calculating the Bit rate: Nominal

TSEG1= 20+14=34
TSEG2=5
BRP=2
Nominal Bit rate = 80Mhz / (2*(34+5+1)) = 1Mbps

In this configuration calculating the Bit rate: Data

TSEG1= 3+3=6
TSEG2=1
BRP=2
Data Bit rate = 80Mhz / (2*(6+1+1)) = 5Mbps

Sampling formula: Sampling Point(%) = (1 + TSEG1) / (1 + TSEG1 + TSEG2), Typical value of sampling point is between 75-90%.
There is no relation between sampling (%) and TDCO.

Hope this calculation will help.

Thanks,
Mudit Bhansali

Hi，

I already know how to calculate SP，For the calculation method of SSP and TDCO still don't quite understand，Can you give an example as you explained SP.

Thanks,

Xinlei Gu

Yes, there is a relation between `trcvDelayCompensationOffset` and the Secondary Sample Point (SSP) percentage.

The `trcvDelayCompensationOffset` is a parameter used in CAN FD to compensate for the delay introduced by the transceiver. This delay can affect the timing of the sample points, including the SSP.

The `trcvDelayCompensationOffset` is typically used to adjust the SSP location to ensure that it falls within the desired range. The SSP percentage is usually calculated based on the bit time, and the `trcvDelayCompensationOffset` is used to fine-tune this calculation.

Thanks,
Mudit Bhansali

In order to get the required SSP(%) , we can adjust the SSP location with the use of trcvDelayCompensationOffset.

SSP Percentage = ((SS + PS1 + (PS2 x (1 - (SSP Location / Bit Time)))) / Bit Time) x 100
where,

- SSP Location is the location of the secondary sample point in time, typically measured in nanoseconds (ns) or microseconds (us).
- Bit Time is the total time for one bit, typically measured in nanoseconds (ns) or microseconds (us).

 In general, the trcvDelayCompensationOffset is used to adjust the SSP location to compensate for the transceiver delay. A positive trcvDelayCompensationOffset value will move the SSP to the right (i.e., later in the bit time), while a negative value will move it to the left (i.e., earlier in the bit time).

ex:

// Calculate the SSP location without compensation
uint32_t sspLocation = (bitTime * sspPercentage) / 100;

// Calculate the SSP location with compensation
uint32_t compensatedSspLocation = sspLocation + trcvDelayCompensationOffset;

// Calculate the new SSP percentage with compensation
uint32_t compensatedSspPercentage = (compensatedSspLocation * 100) / bitTime;

Hi，

1.Through calculation method of the EX, we can through the parameter as shown in figure calculated sspLocation, but we still can't confirm trcvDelayCompensationOffset parameters configured to how much is appropriate. Can you give us an appropriate parameter in the figure and explain why?

In addition, the Can transceiver we used is TCAN1145.

2.According to the information you gave, can I understand that the value of TDCO  can be set as the LOOP DELAY parameter of TCAN1145 (215 or 225ns), as shown in the following figure?

3.If the second is true, can we understand that when sspPercentage is 80%, sspLocation=400ns, The compensatedSspLocation should be equal to sspLocation + trcvDelayCompensationOffset = 400 ns + LOOP DELAY = 400 ns + 215 ns. So compensatedSspLocation is 615ns.

We assume sspPercentage is 100%, So compensatedSspLocation is 500ns+215ns, and the maximum compensatedSspLocation can only be 715ns.

So why is sspPercentage 80%, TDCO is set to 400ns, compensatedSspLocation is 400ns+400ns > 715ns can still collect CAN data normally instead of displaying an error frame.

Thanks,

Xinlei Gu

Xinlei Gu said:

1.Through calculation method of the EX, we can through the parameter as shown in figure calculated sspLocation, but we still can't confirm trcvDelayCompensationOffset parameters configured to how much is appropriate. Can you give us an appropriate parameter in the figure and explain why?

It is recommended to set the TDCO and TDCF to the equivalent amount of time as the DTSEG1. You need to convert the tq of the DTSEG1 register into an equivalent mtq based on the DBRP used.

In your example, the DBRP=5 (400MHz/80MHz), 1tq=5mtq --> TDCO = 5*(17+14)=155mtq

Hi，

Through your description, can I understand that：

DBRP=MCU Clock/ MCAN Clock

TDCO= DBRP* TSEG1=DBRP* (Prop_Seg + Phase_Seg1)

Thanks,

Xinlei Gu

Xinlei Gu said:

2.According to the information you gave, can I understand that the value of TDCO  can be set as the LOOP DELAY parameter of TCAN1145 (215 or 225ns), as shown in the following figure?

The Transmitter Delay Compensation consists of two different delay values. The first delay value is the actual transmitter loop delay and is measured by the device on each transmitted CAN FD frame at the falling edge of the FDF bit to the res bit. The second delay is set by the TDCO mtq configured in the register value.The actual Transmitter Delay Compensation Value (TDCV) is the sum of the loop delay and the TDCO.

The LOOP DELAY (215ns or 225ns in TCAN1145 DS) doesn't include the cable delay. 

Hi Xinlei,

The DBRP defines the length of the time quantum (the basic time unit of the bit time), and the bit timing logic (SEG1, SEG2, SJW) defines the number of time quanta in the bit time. Bit time (ns) is 1000 / baudrate(mbps).

The MCAN functional clock source can be SYS_CLK, XTALCLK, etc. 

The clock source is selected by MSS_RCM_MSS_MCAN0_CLK_SRC_SEL

For example, MCAN FCLK = SYS_CLK / CAN_CLKDIV_SEL Bit

tq = CAN#_CLK / DBRP

bit time = (SEG1 + SEG2 + 1 (Sync) ) * tq

Hi，

According to what you said 1tq=5mtq，TDCO = 5*(17+14)=155mtq，Can I say that TDCO is equal to (CanControllerPropSeg +CanControllerSeg1)*tq

Xinlei Gu said:

Can I say that TDCO is equal to (CanControllerPropSeg +CanControllerSeg1)*tq

Yes, you are correct. The unit of TDCO is mtq. TDCO =  (CanControllerPropSeg +CanControllerSeg1)*tq / mtq

Hi，

I'm going to double-check that the value that TDCO needs to fill in for EB is 387.5ns .TDCO = 5*(17+14)=155mtq=155*2.5ns=387.5ns

Let's know your test result after you finish your test. Thanks

Hi，

What I mean is, if measured in nanoseconds, according to the calculation method you mentioned, would the value of TDCO be 387.5ns?

Thanks,

Xinlei Gu

Yes, you can correct.