TDA4VM: Multiple PTP domains in Linux

Hi,

Jean-Paul da Conceicao said:

1. What would be the best way to access CPTS time of CPSW9 in linux user space on the A72?  My current thinking is that this would require custom driver code on the A72, which registers Time Sync Router callbacks from CPTS on MAIN-R, calculates the clock relationships, and exposes a device in /dev/ptpN?  Does this make sense?

Yes, you need a custom code to get timestamps from R5F because A72 should not access CPTS Timestamp FIFO (architecture limitation) See this E2E You can use IPC, shared memory or any other mechanism. See this for reference

Jean-Paul da Conceicao said:

2. And then accessing CPTS time of CPSW2 on MAIN-R.  I think the only way to do this is to (similarly to the previous case) write some code on the MAIN-R side which registers TSR callbacks from the CPTS of the A72.  The clock relationship can then be calculated, and an abstraction of the clock can be used by applications.  Does this make sense?  Can one use the TSR "backwards" in this way (from A72 to MAIN-R)?

You can already do PTP on Linux for CPSW 2G, why do you want to access it from Main R5F ?

Regards

Vineet

Hi Vineet,

Hope I've understood you correctly: I don't mean actually implementing PTP using timestamps from CPTS, which is what I think you're referring to in your answer?

We just want to be able to synchronize clocks across the cores.  So assume PTP is happening on Linux for the CPSW 2G, and PTP is happening in EthFw for the CPSW9G.  But we want the cores to have access to each other's PTP time.

Is the solution here to use Time Sync Router / hardware push events to schedule periodic callbacks with CPTS and GTC time? Then each core can calculate the offset/rate ratio between GTC and the other core's CPTS.  Or is there a better/easier way?

Examples of why we would want this:

• if we want to send AVB streams from the A72 out on CPSW9G, we need the PTP time of the CPSW9G CPTS here.
• if we want to act as a PTP bridge between CPSW2G and CPSW9G, i.e. we want devices connected to the CPSW9G to be synchronised to a PTP master connected to the CPSW2G.  We would need to somehow convey the PTP time of the CPSW2G to the CPSW9G, so that it can be sent out to PTP listeners.  (Assume a PTP stack here that can act as master and handle 2 domains).

Thanks