AM6442: PTP and PPS via PRU subsystem

Hi Leon,

The version of Linux SDK is not very relevant to your specific question here; I generally ask this question to a better idea of what resources you are working with (i.e. what SDK documentation version, which corresponds to the Linux SDK version, you might be looking at)

-->" I still don't know how to find out on which SoC ball I get the signal. From the EVM datasheet I see on page 48, that PRG0_IEP0_EDC_SYNC_OUT0 is taken from SoC ball W1 and PRG0_IEP0_EDC_SYNC_OUT1 from ball U1. Are those the SoC balls I need to connect to when designing my own board? How do I know which one of the two?"

Both the PRG0_IEP0_EDC_SYNC_OUT0 and PRG0_IEP0_EDC_SYNC_OUT1 signals are synchronization signals generated by the IEP (industrial ethernet sync) module and can be directly mapped to output signals for external devices to use. Additional details about this can be found in the AM6442 TRM "6.4.13.2.6 PRU_ICSSG IEP Sync0/Sync1 Module". I believe you should be able to map either signal to a pin/external device of your choice when designing your own board. 

-->"You write that pin D18 is connected to the PPS. In the manual I see something completely different (see attachment, taken from page 50). Do we mean the same thing?"

I'm looking at the datasheet for AM64x Rev.F and I don't see ball number D18 being connected to the signal name you indicate on page 50 (see below). Try using the datasheet from the product page for AM6442: https://www.ti.com/product/AM6442 

-->"I'd be glad if you found out about the mechanism (CPTS / IEP) behind time synch / PPS via PTP on PRU."

Could you elaborate on what you mean by mechanism? CPTS is the module that handles timestamping for CPSW ethernet while IEP is the module that handles timestamping for PRU_ICSSG ethernet. Both are capable of 1PPS support via PTP but the former does it through CPSW and the latter does it through PRU ethernet.

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After some research, I can see there are two options you can take to get 1-PPS signal generated by IEP (PRU ethernet) on a pin with the AM64x-EVM 

1. Use the default AM64x-EVM device tree file which already includes pin-muxing W7 to signal PRG1_IEP0_EDC_SYNC_OUT0. Note that this is a different signal from the PRG0_IEP0_EDC_SYNC_OUT0 I was investigating earlier. This signal on W7 is already broken out to header J18 that you can directly measure with an oscilloscope to see if 1-PPS shows up after following the instructions in https://software-dl.ti.com/processor-sdk-linux-rt/esd/AM64X/latest/exports/docs/linux/Foundational_Components/PRU-ICSS/Linux_Drivers/PRU_ICSSG_Ethernet.html?highlight=pru_icssg#pps-pulse-per-second-support 

One thing to note here is that there is a known signal integrity issue with this pin when both RGMII ports are active which can lead to the 1-PPS signal to be cut short. If this is a concern you may try option 2.

//Pin-mux snippet from AM64x-EVM DTS file
....
	icssg1_iep0_pins_default: icssg1-iep0-pins-default {
		pinctrl-single,pins = <
			AM64X_IOPAD(0x0104, PIN_OUTPUT, 2) /* (W7) PRG1_PRU0_GPO19.PRG1_IEP0_EDC_SYNC_OUT0 */
		>;
	};
};

2. Route one of the "pr1_edcX_syncY_out" signals from the list below as an input to the Time Sync Router module which can route to the "SYNC0_OUT" signal. The SYNC0_OUT signal can be pinmuxed to ball D18 which leads to a header on J12. The schematic will show J12 is connected to "SYNC1_OUT" which is incorrect, it should be "SYNC0_OUT". I provided a snippet of what I think should be modified on the AM64x-EVM dts file to enable signal "pr1_edc0_sync0_out" to be routed to the "SYNC0_OUT" pin through the time sync router. Please note that I haven't tried this out myself yet so please let me know if you run into issues if you try this.

// Change pinmux from 0 to 1 for D18 to enable SYNC0_OUT
main_ecap0_pins_default: main-ecap0-pins-default {
		pinctrl-single,pins = <
			AM64X_IOPAD(0x0270, PIN_INPUT, 1) /* (D18) SYNC0_OUT */
		>;
	};

// Change the existing timesync_router sub-node from "cpsw_cpts_pps" to be following
&timesync_router {
	status = "okay";
	pinctrl-names = "default";
	pinctrl-0 = <&pru_iep_pps>;

    pru_iep_pps: pru-iep-pps {
        pinctrl-single,pins = <
        /* pps [pr1_edc0_sync0_out = IEP0 sync event 0] in25 -> out8 [pr1_edc0_latch0_in = Selectable time sync event 8] */
        TS_OFFSET(8, 25)
        /* pps [pr1_edc0_sync0_out = IEP0 sync event 0] in25 -> out24 [SYNC0_OUT pin] */
        TS_OFFSET(24, 25)
        >;
    }
};

The Time Sync Router allows for more flexibility because any ICSS/IEP instance and CPTS sync signals can be routed through this module.

-Daolin