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

Products Support DragonBoard 845c
#1

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.

#2

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: Hardware Documentation for DragonBoard 845c - 96Boards

#3

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.

#4

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.

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#5

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

[    1.575891] qcom_geni_serial 88c000.serial: Invalid line -19
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#6

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).

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