Low Speed LS1 UART (Pins 5,7) /dev/XXX port

Hi:

I was trying to figure out what /dev/XXX is mapped to the low speed expansion LS1 UART (Pins 5, 7). If somebody knows it can you please share it.

Thank you.

This is the debug/console UART (ttyMSM0), however this UART is either routed to the low speed connector (LS1) or directly through a FTDI (DEBUG_USB). This is controlled via the dip switch: When Switch 2 set to ON, will force the UART to USB Debug port; when set to OFF, will force the UART to low-speed expansion connector LS1.

source: hardware user manual: https://www.96boards.org/documentation/consumer/dragonboard/dragonboard845c/hardware-docs/

Thank you Loic. I am a little confused from the hardware user manual. Regarding Dip Switch 2 and the UART being routed to DEBUG_USB (2.0) port or LS1 - seems like the hardware user manual is talking about DEBUG_UART (Pins 11, 13) being controlled with Dip switch 2?

And from what I understand from the hardware user manual it sounds like the other UART (Pins 5, 7) is always routed to the LS1?

Essentially I want to write some data to the UART and always get it out of the low-speed expansion connector LS1 - should I use UART (Pins 5, 7)? If so, is it called ttyMSM0?

Thank you very much for helping me clear my confusion.

Correct, but this one is not enabled in the device-tree (sdm845-db845c.dts):

&uart3 {
    label = "LS-UART0";
    status = "disabled";
};

You also need to reference it in device-tree aliases:

aliases {
	serial0 = &uart9;
	hsuart0 = &uart6;
	hsuart1 = &uart3;
};

Then it should appear as /dev/ttyHS1.

However, for now, the firmware does not appear to allow uart protocol on this port… this is I think why it’s not yet enabled.

This seems to be the case. I tried to enable it, got following error:

[    1.575891] qcom_geni_serial 88c000.serial: Invalid line -19

Thank you for your help Loic and Thank you Sumit for confirming. Much appreciate it.

I used /dev/ttyMSM0 and it works. I wrote some messages to /dev/ttyMSM0 and I see that appearing on the debug USB port. Next I will try to route /dev/ttyMSM0 to the LS1 (using the dip switch).