01 ? ? 456789ab

[Alma J Wetzker]

Vu Pham wrote:
> My Linux box has 2 standard serial ports ttyS0 and ttyS1. I just added a
> ByteRunner PCI-800H that has 8 serial ports. Linux detects it without any
> problem and adds the 8 ports starting at ttyS4.
> 
> I went into the BIOS setup and found only two serial ports. 
> 
> I wonder which devices keep the port ttyS2 and ttyS3 ?
> 
> Thanks,
> 
> DT

This is a legacy PC type issue.  The original IBM PC defined ports for 
four serial ports, com1:4.  There were only two interrupts reserved for 
serial ports, this was in the bad old days of ISA bus where interrupts 
could not be shared.

Rather than deal with the many work arounds that the various chip sets 
and BIOS's have implemented over the years, linux, wisely, starts adding 
multiple serial ports after the first four, reserved ports.

I suspect that if you really wanted, you could get a PCI serial card to 
implement the first four ports at the defined addresses.  Then you 
should not have the gap in port numbers.  Of course, who uses the old 
RS-232 serial ports any more? <grump>

     -- Alma