[GTALUG] Actual ttyS0 MIA

[Stewart C. Russell]

On my desktop (i7-4790K, 32 GB DDR3, Asus H97M-E) I've run out of serial 
ports I can usefully access via USB serial adapters*. The motherboard 
does have a real COM port on it, though, and just after I built the 
system I added an adapter cable/bracket (one of these, IIRC: 
https://www.canadacomputers.com/product_info.php?cPath=5_1336_1449&item_id=094057). 
But it's never worked as a port, and I want to make it work.

It's enabled in the BIOS and Linux (Ubuntu 19.10) finds it:

     ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A

I'm a member of `dialout`, and the ports seem to check out:

     $ ls -l /dev/ttyS0 /dev/ttyUSB0
     crw-rw----  1 root dialout   4, 64 May  6 21:54 /dev/ttyS0
     crw-rw----+ 1 root dialout 188,  0 May  3 07:50 /dev/ttyUSB0

No data goes in or out. Curiously `stty -F /dev/ttyS0` hangs for a few 
seconds, but that's the only odd thing I see.

Hardware serial ports are kind of ancient history. Anyone remember 
ancient magic to make 'em work? There's a chance that ASUS don't use the 
standard serial pin header assignment: I'll trace that if necessary.

thanks,
  Stewart

*: you run out of ways to identify the interfaces via /dev/serial/*. 
Unless I reinvested a fortune in real FTDI adapters with unique serial 
numbers, I'm kind of stuck. I currently use: 1 real FTDI, 1 knock-off 
FTDI, a QinHeng HL-340, a Prolific PL2303 and a Silicon Labs CP210. I 
have another knock-off FTDI and another Prolific, but they identify 
identically and make device selection problematic.