To enable the second serial port you must enable it in the kernel configuration (make xconfig). And do additional kernel config changes:
1. In "Character devices" set "n" the option in "Disable COM A". "Disable COM B" /must be in "y" by default).
2. In "Character devices" set "TTYS1" as console. The console is connected to "COM B" of the NS7520 but when only one serial port is enabled (as by default) is set as "ttyS0", but if you enable the "COM A" (disabled by default, and the real COM you want to use) the "COM A" becomes "ttyS0" and "COM B" "ttyS1".
3. In "General setup" you must set "y" "Compiled-in Kernel Boot Parameters" and change "console=ttyS0" to "console=ttyS1" (the same reason as in point 2).
4. You must change the inittab file in /etc to set the console to ttyS1 instead of ttyS0:
#::respawn:/sbin/agetty /dev/ttyS0 /bin/sh -l
::respawn:/sbin/agetty /dev/ttyS1 /bin/sh -l
With all this changes you keep ttyS1 as your previous ttyS0 and now the ttyS0 is your new added serial port...
Last updated:
Jun 21, 2019