IWR6843: Connecting multiple radars on CAN

Hey Manoj,

First of all, I will need some more insight into how you are transmitting and receiving data. What is your current mcanCfgParams, mcanBitTimingParams, and rxMsgObjectParams and txMsgObjectParams? 

Additionally, have you verified the following?

• Both ends of the CAN line should be terminated with a 120 ohm resistor between the CAN low and CAN high lines to prevent reflections from impedance mismatching
• Ensure all nodes are set to the same timing parameters - i.e. bit rate, propogation segment, phase segments, sync jump width, prescalar, etc.

Regards,

Kristien

Hi Kristien,

Please find the attached images below for mcanCfgParams, mcanBitTimingParams, and rxMsgObjectParams and txMsgObjectParams,

I have verified those two points also, everything is fine.

I have one query regarding CANFD_Init function. Please find the screenshot below,

Above this function there is a comment mentioned that "Currently only 1 instance of CANFD is supported. Valid value is 0." So is there possibility of having same instance id which are clashing on CAN bus and at a time only one CAN RADAR is communicating on CAN BUS. Because of having same instance id, the one who win the CAN bus access will be able to communicate and not the other one.

Thanks,
Manoj

Hey Manoj,

The CAN-FD driver should support being able to use both CAN instances simultaneously, though I've only personally tested using the two transceivers on two separate buses. If you want to instantiate the second CAN transceiver, you will have to call CANFD_init again with ID 1 and setup new bit timings and message objects for it. You can see an example of how this is done in the 6843 CAN-FD driver binary unit test (<MMWAVE_SDK_INSTALL_DIR>/packages/ti/drivers/canfd/test/xwr68xx/main.c) under the mcanDualMsgIdRangeTest and mcanDualMultiTransmission functions.

I also wanted to clarify that when you only get data from one transceiver, i.e., the first one to power on, do you only get data from that one transceiver for the entirety that all transceivers are on? In other words, until you power cycle all nodes simultaneously, the first node on, or perhaps the oldest node, will have priority?

Have you checked the signals on the bus to verify whether this behavior could be linked to arbitration? Keep in mind that all nodes read back the bus value when transmitting identifier and RTR bits, and a node will stop transmitting if it transmits a recessive bit but reads back a dominant bit.

Regards,

Kristien

Hi Kristien,

So, what I understood from this is having same instance ID is not an issue, right? That means having same instance ID for multiple RADARs "CANFD_init(0, &mcanCfgParams, &errCode);" is fine. Let me know if my understanding is correct.

I also wanted to clarify that when you only get data from one transceiver, i.e., the first one to power on, do you only get data from that one transceiver for the entirety that all transceivers are on? In other words, until you power cycle all nodes simultaneously, the first node on, or perhaps the oldest node, will have priority? 
Ans: Yes, you are right. I am getting data only from that one transceiver which is powered on first. I have done some experiment on this; I have pressed the reset button of two RADARs and released reset button of one of them and later the other one. So, which one reset button released first started giving me the data for entire session. 

Have you checked the signals on the bus to verify whether this behavior could be linked to arbitration?
Ans: I suspect this is happening. The one which is powered on is holding the bus and not releasing it. Can we do anything like once packet is sent then that RADAR can release the bus or something like that?

Thanks,
Manoj

Hey Manoj,

Manoj Wakdikar said:

So, what I understood from this is having same instance ID is not an issue, right? That means having same instance ID for multiple RADARs "CANFD_init(0, &mcanCfgParams, &errCode);" is fine. Let me know if my understanding is correct.

That is correct. The instance ID is used to address which CAN transceiver to use on the device, i.e., either CAN 0 or CAN 1.

The radar CAN should release the bus after sending the last 7 bits (IFS) of a CAN frame. Is the bus still being pulled low even after a message ends? As far as I know, once a transmission buffer request has been made, the CAN transceiver will handle sending out the message.

Regards,

Kristien

Hi Kristien,

I found this thread, https://e2e.ti.com/support/sensors-group/sensors/f/sensors-forum/1297380/iwr6843aop-can-fd-multiple-devices

By referring those modifications mentioned in this thread now I am able to communicate two radars on same CAN bus. But it is also mentioned in that thread that user doesn't know about the circumstances of making those changes. Do you have any further input on this? Is it correct doing these changes?

Thanks,
Manoj

Hey Manoj,

As Adam mentioned in his replies, it appears that disabling the error and data interrupts allows him to receive messages on other non-radar CAN interfaces, but that he's unable to receive with radar CAN interfaces as a result. 

As such, one possible solution could be to use a polling method to continuously check the NDAT register (New Data - triggered by a buffer receiving new data) or the FIFO status register (fill level should increase when a message has been received) and then read the respective source when a change is detected.

Alternatively, the radar CAN receiving issue could be a result of some of the nuisances of acceptance filtering. I would highly recommend reading Section 3.4 of the Bosch MCAN User Guide, particularly Figure 6, and checking the relevant GFC fields in your software initialization. Note that there are some differences in buffer vs. FIFO receiving which is primarily outlined in Section 3.4.1 Acceptance Filtering.

Regards,

Kristien

Hi Kristien,

Thank you for suggesting possible solution. And thank you for the recommending the document, I will look into that document.

Regards,
Manoj

Hey Adam,

I appreciate you offering your help on this thread. Do you know what settings you used for your GFC parameters?

Regards,

Kristien

Hi Adam,

Thank you so much for your help. It really helped with your older thread and thank for offering help in this thread. So right now, I am communicating with 2 CAN radars. I am getting data from 2 radars.

Further this did you make any changes to rectify the things like which changes are required and which not? And what changes you made to successfully configure the radars?

As Kristien said it will be very helpful if you can let us know about the settings you used. It will be highly appreciated.

Thanks,
Manoj

Hi,

The CFG parameters are essentially the same as those posted at the beginning of this thread. I believe that if you are able to retrieve data from two devices, the parameters are correct.

I am using a modified OOB demo with a hard-coded configuration for the initial sensor startup. To further configure the sensor over CAN, I implemented message reception within the MCANAppCallback. The received messages (collected from multiple messages) are then passed to the CLI_task method in cli.c, in the same manner as if UART were being used. Note that UART_read is commented out due to its blocking nature.

Is there anything specific that is not working for you right now?

Adam

Hi Adam,

Thank you for your response. Right now, I am not facing any issues as such. But I have not yet tried configuring the radars. I am just taking data from radar; you can say one way communication happening as of now. I will try configuring the radars over CAN and if I face any issues will post it here. 

Regards,
Manoj

Hey Manoj,

Another thread on handling multiple sensors on one CAN bus was recently resolved. I asked for more details on the final configuration they are using, but the poster indicated that setting the ANFE and ANFS fields to 3—i.e., reject non-matching frames—resolved their issue. You could attempt to test this on your side to see if this works on your CAN setup.

Regards,

Kristien

Kristien Everettthank you for sharing some more insights. I will try that too and let you know.

Adam, I have one query that you modified those parameters to work multiple radar over CAN and it worked. So what thing lead you there and you thought of changing these parameters? I just want to know the idea/reason came in your mind that if you modify those parameters then multiple radars can work over CAN.

Thanks,
Manoj

Hi Adam,

Thank you for sharing your CAN configuration.

My application is, I am using radars for obstacle avoidance. These radars will be mounted on UAS (Unmanned Aerial System). So, in my application I am also taking inputs from all the radars and processing it further for obstacle avoidance application.

Regards,
Manoj

Once again, thanks for hopping on this thread Adam Koutny and sharing your configuration. 

Manoj Wakdikar If you get the chance to test Adam's configuration or modify your configuration to reject non-matching frames, please let us know the result. 

Regards,

Kristien

Thank you so much Kristien and Adam. 

Adam this configuration worked for me. This is really a great help for me. 

Thank you once again to both of you.

Regards,

Manoj

Hey Manoj,

I'm glad Adam's configuration worked out for you! There have been a few others facing issues interfacing with multiple radar devices over CAN before, but I haven't had the chance to do testing to determine a configuration that seems to generally work with multiple CAN nodes. Its nice that there's a post I can point them to as a starting point in the future!

Adam Koutny Looks like I owe you a beer now too! 

Regards,

Kristien

Hi Kristien and Adam,

This is one the best thread to me. Collaboration of us and brainstorming in this thread really helped a lot.

Thank you so much for your help, guys. Cheers...! 

Regards,
Manoj

Hi,

I'm glad it is working. I enjoyed this thread as well!

See you in the next thread, guys!

Cheers!

Adam