This is a small guide to configure extended serial ports based on my work when building embedded linux on WAFER-LX2 SBC.
On 2.6 kernel:
Make sure kernel has support for Extended 8250/16550 serial driver (CONFIG_SERIAL_8250_EXTENDED)
Device drivers -> Character devices -> Serial drivers
- Support for more than 4 legacy serial ports (CONFIG_SERIAL_8250_MANY_PORTS)
- Support for sharing serial interrupts when needed (CONFIG_SERIAL_8250_SHARE_IRQ)
Set how many serial ports to be registered at runtime or via kernel command line option:
8250.nr_uarts=x
It's very recommended to disable autodetect IRQ on standard ports
(CONFIG_SERIAL_8250_DETECT_IRQ) and use setserial command (eg. boot script)
Example:
/sbin/setserial /dev/ttyS4 port 0×338 irq 4 uart 16550A baud_base 115200
To show all serial ports configuration:
/sbin/setserial -bg /dev/ttyS*
Note:
I got invalid argument when baud_base was not issued by setserial command (setserial 2.17)
To make the port setting permanent, add any port(s) to /etc/serial.conf and run setserial on boot (boot script, i.e rc.serial)
Use terminal emulation i.e minicom for testing purposes.
Some related files:
- /proc/tty/driver/serial -> list serial ports address, irq, tx/rx mappings
- /etc/serial.conf -> serial port configuration
- kernel/Documentation/serial/driver -> serial low level API
