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I am trying to use an external modem and I have four serial ports. I can connect the modem to ttyS0 and query it using kermit fine, but then when I connect it to ttyS1 it doesn't respond and I experience the same behaviour for the other ports.
The ports seem to be detected normally and they exist. If I cat /proc/tty/driver/serial while ttyS0 is working correctly with my modem, it says this:
I notice that RTS|CTS|DTR has disappeared from line 0 and moved to line 1 but also, DSR|CD|RI is present on line 1. I am guessing this is why it's not working. I am assuming that if DSR|CD|RI was not present on line 1 then it would work.
Is there a way to get lines 1, 2 and 3 to behave like line 0 so that they work?
I have fixed this now. The problem was with the IRQs. It turned out that ttyS2 and ttyS3 shouldn't have been IRQ 4 and 3 respectively. Instead, they were IRQs 10 and 11.
I used setserial to change the IRQ of ttyS2 and then it worked..... sort of.
/proc/tty/driver/serial still shows the same signals for the ports, so it still shows RTS|CTS|DTR|DSR|CD|RI for ttyS1 when it's in use, but this time it works. I was therefore wrong about the presnce of DSR|CD|RI causing a problem.
However, when I try and change the IRQ of ttyS3, it actually changes the one for ttyS2!
I use this command:
setserial /dev/ttyS3 irq 11 port 0x2e8