TMS320F28388D: What is the minimum delay required between two message transmission over CAN

Abhijit Dasgupta

Part Number: TMS320F28388D
Other Parts Discussed in Thread: TMS320F28379D

Hello Experts,

I am sending multiple messages from 10ms schedular over CAN A/B. I have around 35 Tx and 7 RX messages to send and received. I am currently using TMS320F28388D controller. What I could see is, when I continuously send messages (3-5) message on each 10ms frame, I see some TX rate for some message rates are not consistent. Even some are not getting transmitted as well. As timing is critical for aerospace application i have to fix this, hence I would like to seek your opinion about below questions:

1. What is the minimum time delay required between two transmissions/Receptions?

2.Does this TXOK bit from CAN_ES register determines the transmission is completed, nothing pending?

3.Is it really required to generate an interrupt once a message is transmitted to detect whether transmission is completed successfully?

In some TI e2e blogs, I saw that minimum of 135us delay is required to complete between two message transmission. This e2e post was for TMS320F28379D controller I believe, is it valid for TMS320F28388D controller also?

The driver was developed considering pulling method, no interrupt methods implemented.

please see the rates column, its fluctuating in the below video. I am looking for your response on the same

6 months ago

0 Hareesh Janakiraman 6 months ago

TI__Guru* 95315 points

Abhijit,

This is a complicated question. Much depends on what else the CPU is doing, in addition to handling CAN traffic.

Abhijit Dasgupta said:
1. What is the minimum time delay required between two transmissions/Receptions?

There is no such requirement. In one go, you can mark multiple message objects for transmission. When the bus is sensed to be idle, they will be transmitted one after another in the order of message object priority. Of course, if other nodes in the bus attempt to transmit, CAN bus arbitration rules come into play.

Abhijit Dasgupta said:
2.Does this TXOK bit from CAN_ES register determines the transmission is completed, nothing pending?

No. It only indicates that the last transmission was successful. i.e. acknowledged by at least one node on the network. It does NOT indicate that all pending transmissions have been completed.

Abhijit Dasgupta said:
3.Is it really required to generate an interrupt once a message is transmitted to detect whether transmission is completed successfully?

That is completely up to the application. In a majority of the applications, the CPU has to cater to multiple peripherals, so polling is impractical and usage of interrupts becomes inevitable.

Abhijit Dasgupta said:
In some TI e2e blogs, I saw that minimum of 135us delay is required to complete between two message transmission.

That is incorrect. 135us is the average time it takes to transmit a frame with an extended identifier.

Abhijit Dasgupta said:
This e2e post was for TMS320F28379D controller I believe, is it valid for TMS320F28388D controller also?

Yes, it applies to any device with a CAN module.

0 Abhijit Dasgupta 6 months ago in reply to Hareesh Janakiraman

Prodigy 80 points

Is there a way to get the mailbox status stating that, the previous transmission of the selected mailbox is completed its available to be used for next message.

For example, Let's say I have configured mailbox 20 for one message, now the transmission is done, I have to use the same mailbox for Receiving new message or transmitting another message. I have this scenario as I have more TX & RX messages more than 32 mailboxes.

0 Hareesh Janakiraman 6 months ago in reply to Abhijit Dasgupta

TI__Guru* 95315 points

You can poll the TxRqst bit for the corresponding message object in CAN_TXRQ_21 Register

From the TRM:

"After a successful transmission and if no new data was written to the message object (NewDat = 0) since the start of the transmission, the TxRqst bit is reset".

0 Hareesh Janakiraman 6 months ago in reply to Hareesh Janakiraman

TI__Guru* 95315 points

Please download my Application report http://www.ti.com/lit/SPRACE5 and read through the Debug tips carefully. Most CAN issues can be resolved by going through this checklist.

The TRM chapter explains the CAN protocol implementation in the MCU. i.e. it explains the functions of the various registers/bits. However, it does not explain the protocol itself. For protocol information, refer to these excellent videos:

https://training.ti.com/automotive-can-overview

https://training.ti.com/ti-precision-labs-canlinsbc-can-and-can-fd-protocol?context=1139747-1138099-1139707-1138111

https://training.ti.com/ti-precision-labs-canlinsbc-can-and-can-fd-overview?context=1139747-1138099-1139707-1138109

https://training.ti.com/ti-precision-labs-canlinsbc-can-physical-layer?context=1139747-1138099-1139707-1138110

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TMS320F28388D: What is the minimum delay required between two message transmission over CAN