DRA77P: CAN messages buffered by transceiver

AClemotte

Part Number: DRA77P

I need to meet the following requirement: "The CAN bus channel shall support wake-up functionality and the initial CAN messages can be buffered by the controlling processor"

I understand that the issue of waking up by a CAN message is resolved as discussed here with the TCAN1043-Q1:

However, it is not clear to me if the transceiver has a buffer capable of storing messages. If so, what capacity does the buffer have? If not, what options do you have to solve this?

Regards,

over 6 years ago

0 Karan Saxena over 6 years ago

TI__Guru* 78165 points

Hi,

Can you help me in understanding the requirement of "initial CAN messages can be buffered by the controlling processor" a little more?

Regards,

Karan

0 AClemotte over 6 years ago in reply to Karan Saxena

Expert 1060 points

Hi Karan,

The sequence we expect is as follows:

The system is off (power-off)
The transceiver detects a request to wake-up on the CAN bus and signals it using the INH pin (TCAN1043-Q1).
INH pin will go to the power circuit, and will power-on the system
System power-on will take about 2 seconds to complete.

During these 2 seconds we do not want to lose any CAN message and the transceiver should be able to buffer them until the system is awake and ready to process the CAN messages. The question is if there is any transceiver with a buffer, capable of temporarily storing a limited group of messages. We are still unclear about the size of the buffer, but at least I would like to know if this type of device exists.

Regards,

0 Karan Saxena over 6 years ago in reply to AClemotte

TI__Guru* 78165 points

Hi,

I see what your use-case is, but I would say 2sec will be a lot of time in practical CAN networks. You might receive 1000s of messages during that period and no Transceiver would be able store so many messages.

What I would suggest is, in the boot sequence try to boot the CORE controlling the CAN first, that way the time to get the CAN interface up should significantly reduce. The early can response in the latest SDK 6.02 is around 60ms (http://downloads.ti.com/jacinto7/esd/processor-sdk-rtos-jacinto7/latest/exports/docs/mcusw/mcal_drv/docs/drv_docs/demo_boot_app_mcu_rtos_top.html)

Meanwhile I am checking with the TCAN team on the transceiver side.

Regards,

Karan

0 AClemotte over 6 years ago in reply to Karan Saxena

Expert 1060 points

Hi Karan,

I completely agree that the transceiver buffer can be easily filled. Also I want to tell you that our SW team is working with speeding up the boot to lose as little CAN messages as possible. For my part, to lose even fewer messages, I would like to know if there are CAN transceivers with some kind of buffer.

Regards,

0 Karan Saxena over 6 years ago in reply to AClemotte

TI__Guru* 78165 points

Hi,

I have a meeting with the TCAN team today, will post a reply stating what came out of the discussion.

Regards,

Karan

0 Karan Saxena over 6 years ago in reply to Karan Saxena

TI__Guru* 78165 points

Hi,

Just got off the call from the TCAN team.

The buffering in the CAN transceiver is most likely not possible the reason being that the transceiver is protocol agnostic and hence to interpret the CAN message will be a challenge. I thing we would have to live with the fact that there could be messages which are lost in case there is traffic coming in on the bus during the time the wakeup is happening, the way we can lose less is ofcourse to have the core booting early and taking control.

The current SDK offering is the early CAN response of around 60ms (http://downloads.ti.com/jacinto7/esd/processor-sdk-rtos-jacinto7/latest/exports/docs/mcusw/mcal_drv/docs/drv_docs/demo_boot_app_mcu_rtos_top.html).

Regards,

Karan

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DRA77P: CAN messages buffered by transceiver