SK-AM62P-LP: UART Com from Linux SDK

Hi Bin Liu,

I have checked the menuconfig first and found that it's already enabled by default.
So, I directly changed the device tree file(k3-am62p5-sk.dts) for main_uart5 by reference to a similar file for main_uart1.

aliases {
		serial0 = &wkup_uart0;
		serial2 = &main_uart0;
		serial3 = &main_uart1;
		serial5 = &main_uart5;
		mmc0 = &sdhci0;
		mmc1 = &sdhci1;
		mmc2 = &sdhci2;
		spi0 = &ospi0;
		ethernet0 = &cpsw_port1;
		ethernet1 = &cpsw_port2;
		usb0 = &usb0;
		usb1 = &usb1;
	};
main_uart5_pins_default: main-uart5-default-pins {
		pinctrl-single,pins = <
			AM62PX_IOPAD(0x1d8, PIN_INPUT, 1)	/* (B23) UART0_RXD */
			AM62PX_IOPAD(0x1dc, PIN_OUTPUT, 1)	/* (F20) UART0_TXD */
		>;
		bootph-all;
	};
	
&main_uart5 {
	pinctrl-names = "default";
	pinctrl-0 = <&main_uart5_pins_default>;
	/* Main UART5 is used by USER firmware */
	status = "okay";
	bootph-all;
};

root@am62pxx-evm:~# cat /proc/tty/driver/serial
serinfo:1.0 driver revision:
0: uart:unknown port:00000000 irq:0
1: uart:unknown port:00000000 irq:0
2: uart:8250 mmio:0x02800000 irq:251 tx:20146 rx:429 RTS|DTR|DSR
3: uart:unknown port:00000000 irq:0
4: uart:unknown port:00000000 irq:0
5: uart:8250 mmio:0x02850000 irq:253 tx:8016 rx:7561 DSR
6: uart:unknown port:00000000 irq:0
7: uart:unknown port:00000000 irq:0
8: uart:unknown port:00000000 irq:0
9: uart:unknown port:00000000 irq:0
10: uart:unknown port:00000000 irq:0
11: uart:unknown port:00000000 irq:0
root@am62pxx-evm:~# dmesg | grep base_baud
[    1.669955] 2800000.serial: ttyS2 at MMIO 0x2800000 (irq = 251, base_baud = 3000000) is a 8250
[    1.684830] 2850000.serial: ttyS5 at MMIO 0x2850000 (irq = 253, base_baud = 3000000) is a 8250

Hi Bin Liu,

Now it's working. Thanks very much for your support. Actually, I have tried the same before, but the disable thing I wasn't aware of, and in the document, it's also not available, I guess.

Regards,
Debashis

Hi Bin,

Now I am not able to run that stty command its stuck. And I am having the same problem. Can to tell me how can I verify that it's reverted to 115200 and am I have to do it every time or is there any method to fix it?

Issue:

root@am62pxx-evm:~# systemctl disable serial-getty@ttyS5.service
Removed '/etc/systemd/system/getty.target.wants/serial-getty@ttyS5.service'.
[ 1461.657287] systemd-ssh-generator[1271]: Binding SSH to AF_UNIX socket /run/ssh-unix-local/socket.
[ 1461.658092] systemd-ssh-generator[1271]: → connect via 'ssh .host' locally
[ 1461.686934] systemd-sysv-generator[1273]: SysV service '/etc/init.d/ethercat' lacks a native systemd unit file. ️ Automatically generating a unit file for compatibility. Please update package to include a native systemd unit file, in order to make it safe, robust and future-proof. ️ This compatibility logic is deprecated, expect removal soon. ️
root@am62pxx-evm:~# stty -F /dev/ttyS5 115200 -echo

Regards,
Debashis

Hi Bin,

I saw this print statement also from the kernel side.

[ 258.795712] audit: type=1112 audit(1735627359.362:243): pid=886 uid=0 auid=4294967295 ses=4294967295 subj=kernel msg='op=login acct="oohhh" exe="/usr/bin/login" hostname=am62pxx-evm addr=? terminal=ttyS5 res=failed'

Hi Bin,
When I run simple write and read code to read the uart data you can see the erratic behavior.

root@am62pxx-evm:/home/uart# ./serial_posix 
Read from serial port: Hello, Serial Port!
Login incorrect

root@am62pxx-evm:/home/uart# ./serial_posix 
Read from serial port: Hello, Serial Port!
root@am62pxx-evm:/home/uart# ./serial_posix 
Read from serial port: Hello, Serial Port!
root@am62pxx-evm:/home/uart# ./serial_posix 
Read from serial port: Hello, Serial Port!
root@am62pxx-evm:/home/uart# ./serial_posix 
Read from serial port: Hello, Serial Port!
root@am62pxx-evm:/home/uart# ./serial_posix 
Read from serial port: p
am62pxx-evm login: 
am62pxx-evm login: Debian GNU/Linux trixie/sid am62pxx-evm ttyS5
p
am62pxx
root@am62pxx-evm:/home/uart# ./serial_posix 
Read from serial port: -evm login: 
am62pxx-evm login: Debian GNU/Linux trixie/sid am62pxx-evm ttyS5
p
am62pxx-evm login
root@am62pxx-evm:/home/uart# ./serial_posix 
Read from serial port: : 
am62pxx-evm login: Debian GNU/Linux trixie/sid am62pxx-evm ttyS5
p
am62pxx-evm login: 
am62px

Hi Debashis,

The Processor SDK rootfs provides a UART tool called serialcheck. Please use this tool to check UART read and write access.

Hi Bin,

You can take a look at the screenshot.
I have one doubt that cts and rts are required to run this serial check because I just connected the RX to TX with the jumper wire.



Regards,
Debashis

Hi Debashis,

Since you didn't connect cts and rts pins, please run serialcheck program without '-h' option to not use hardware flow control.

Hi Bin Liu,

I have gone through the code of serialcheck.c and I have some doubts about it.

1. we are setting it to read 64 bytes and the time out 0.8sec with blocking read and write because it's using this function(ret = fcntl(fd, F_SETFL, 0);)

new_term.c_cc[VMIN] = 64;
new_term.c_cc[VTIME] = 8;

Hi Debashis,

This seems to be related to kernel TTY framework or Linux userspace terminal programing, not related to the platform UART module, sorry I don't have an answer.