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I have a host where I run minicom and there is a board with two serial ports (ttyS4,ttyS5). I connect board to host with serial to usb which is identified as ttyUSB0 in my host.

When I set kernel command line parameter as console=tty0 console=ttyS0,115200n8 and configure getty for ttyS0 for login, I can get the serial console messages on my minicom, but I want to set console parameter as ttyS5 and get the console messages on my minicom. But setting ttyS5 does not give the console messages. The baud rate for ttyS5 as per setserial is :

/dev/ttyS5, Line 5, UART: 16550A, Port: 0x0000, IRQ: 11
    Baud_base: 3000000, close_delay: 50, divisor: 0
    closing_wait: 3000
    Flags: spd_normal

And the command line parameter I set for kernel to use ttyS5 as serial console is console=ttyS5,115200n8 console=tty0

I tried changing the baudrate to 3000000 in kernel command line but no use. In host minicom the baudrate is set to 115200. I also tried to change baud base with stty -F /dev/ttyS5 115200 but it remains same.

Below is the output of proc/tty/driver/serial:

serinfo:1.0 driver revision:
0: uart:16550A port:000003F8 irq:4 tx:0 rx:0 CTS
1: uart:16550A port:000002F8 irq:3 tx:0 rx:0
2: uart:unknown port:000003E8 irq:4
3: uart:unknown port:000002E8 irq:3
4: uart:16550A mmio:0xFEDC6000 irq:10 tx:0 rx:0 CTS|DSR|CD|RI
5: uart:16550A mmio:0xFEDC8000 irq:11 tx:16 rx:0 RTS|CTS|DTR|DSR|CD|RI

I am using amd64 board with two physical uart serial ports. Is there any way to use ttyS5 serial port as the serial console?

  • Baud_base is not the same thing as the baud rate: it is the "base clock" used to generate the various baud rates by dividing the base clock rate. By modifying baud_base, you can get older software that cannot set higher baud rates on their own to use higher speeds. Your ttyS4 and ttyS5 may be PCI-based and so unsuitable for use as real console devices: they won't be usable for the Linux kernel until the PCI configuration is complete, which misses a lot of early boot events. – telcoM May 14 '18 at 7:13

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