Sensor synchronization with SPE and Orin processor

In a system with multiple sensors, I’d like to create timestamps for sensor data in order to synchronize the different sensors. Assume that some sensors are connected to the Orin main processor and some are connected to the Sensor Processing Engine (SPE). The main processor uses an RTC clock that represents the reference time source of the system. How can I synchronize all sensors in the sytem?

I realize that there is the Generic Timestamp Engine that can be used to monitor GPIOs of the SPE. Assume, however, that I use an SPE GPO to trigger a sensor reading and want to create a timestamp for that trigger. Is this possible with the Generic Timestamp Engine? Where can I find more information regarding this driver?

Thank you,
David

Hello,
I’m not quite clear about your statement by ‘main processor uses an RTC clock that represents the reference time source of the system’.

Within the whole Orin chip, generally a global TSC is used for timestamp. And you can take a look at TRM for details.

Back to your question, yes, GTE can record timestamps for GPIO events, as GTE demo in SPE firmware package shows.

If you are using different timestamp source between CCPLEX and SPE, you may have to convert one to a unique timestamp base. It’s highly application-dependent.

br
Chenjian

Hi Chenjian,

Thank you for your response and sorry if my question was not clear.

When I said “The main processor uses an RTC clock that represents the reference time source of the system.” I meant the internal RTC of the SoC.

Thank you for pointing me at the TSC. The GTE can be used to read timestamp events recorded in the SPE from the CCPLEX, is that correct?

Thank you,
David

Hello, David:
Sorry that I’m still confused for RTC as timestamp. The clock source of RTC is only 32khz, and it may be quite inaccurate for a timestamp.

yes, GTE can be used to record timestamp, and also, you can get timestamp in ISR (SW implementation).

br
ChenJian

Hello ChenJian,

so to sum it up: TSC should be used to generate timestamps and the GTE can be used to communicate timestamp events from the SPE to the CCPLEX. Is that correct?

Regards,
David

Hello, David:
Not so exactly.
TSC is a read-only timestamp counter, and it’s sync inside the SOC. You can take it as a global TS for the chip. For example, both CCPLEX and SPE can read TSC to get a same counter if the read operations are exactly in the same time.
GTE is just a generic timestamping engine, and it can record the timestamp of events like GPIO toggle. It has nothing to do with communications between SPE and CCPLEX.

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ChenJian

Hi ChenJian,

thanks for the clarification. If I understand Generic Timestamp Engine — Jetson Linux<br/>Developer Guide 34.1 documentation correctly, the GTE can run on the CCPLEX domain while monitoring GPIOs in the SPE domain. Correct?

Thank you,
David

Hello, David:

the GTE can run on the CCPLEX domain while monitoring GPIOs in the SPE domain

Honestly, I have not tried so. But I think as long as GPIO interrupt mapping (to CCPLEX) is good, GTE should work as well. Also, you may have to check the GTE driver in Linux side.

br
ChenJian

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