How do I specify that a serial port should, or should not, ignore the state of the Carrier Detect line?
Prior to SunOS 4.1, you do so either by: changing the “flags” field for the serial port device in the kernel “config” file, re-running “config”, rebuilding the kernel, and rebooting with the new kernel; or, on the Sun-4c machines: changing the setting of the “ttya-ignore-cd” or “ttyb-ignore-cd” EEPROM settings if the port is one of the CPU serial ports. In SunOS 4.1 (and, I think, some SunOS 4.0[.x] releases for the Sun386i), you do so by changing the “/etc/ttytab” line for the port in question to have the “local” attribute if CD is to be ignored, or not to have it if CD is not to be ignored, and running the “ttysoftcar” command to tell the kernel that the status of the “ignore CD” flag should be changed. In 4.1, there’s no need to change the EEPROM setting to change SunOS’s behavior; it may affect the PROM’s behavior, but that’s the only reason why it’d be necessary.
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