Hardware manual

number to it.

Your port does have a ttyS number assigned to it (like ttyS14) but you don't know which physical

connector it is (on the back of your PC). See Which Connector on the Back of my PC is ttyS1, etc?

First check BIOS messages at boot-time (and possibly the BIOS menu for the serial port). Then for the PCI

bus type lspci -v. If this shows something like "LPC Bridge" then your port is likely on the LPC bus which is

not well supported by Linux yet (but the BIOS might find it) ?? If it's an ISA bus PnP serial port, try

"pnpdump --dumpregs" and/or see Plug-and-Play-HOWTO. If the port happens to be enabled then the

following two paragraphs may help find the IO port:

Scanning/probing legacy ports

This is mainly for legacy non-PCI ports and ISA ports that are not Plug-and-Play.

Using "scanport" (Debian only ??) will scan all enabled bus ports and may discover an unknown port that

could be a serial port (but it doesn't probe the port). It could hang your PC. If you suspect that your port may

be at a certain address, you may try manually probing with setserial, but it's a slow tedious task if you have

several addresses to probe. See Probing.

16.5 Linux Creates an Interrupt Conflict (your PC has an ISA

slot)

If your PC has a BIOS that handles ISA (and likely PCI too) then if you find a IRQ conflict, it might be due to

a shortage of free IRQs. The BIOS often maintains a list of reserved IRQs, reserved for legacy ISA cards. If

too many are reserved, the BIOS may not be able to find a free IRQ and will erroneously assign an IRQ to the

serial port that creates a conflict. So check to see if all the reserved IRQs are really needed and if not,

unreserve an IRQ that the serial port can use. For more details, see Plug-and-Play-HOWTO.

16.6 Extremely Slow: Text appears on the screen slowly

after long delays

It's likely mis-set/conflicting interrupts. Here are some of the symptoms which will happen the first time you

try to use a modem, terminal, or serial printer. In some cases you type something but nothing appears on the

screen until many seconds later. Only the last character typed may show up. It may be just an invisible

<return> character so all you notice is that the cursor jumps down one line. In other cases where a lot of data

should appear on the screen, only a batch of about 16 characters appear. Then there is a long wait of many

seconds for the next batch of characters. You might also get "input overrun" error messages (or find them in

logs).

For more details on the symptoms and why this happens see Interrupt Problem Details and/or Interrupt

Conflicts and/or Mis-set Interrupts. If it involves Plug-and-Play devices, see also the Plug-and-Play-HOWTO.

As a quick check to see if it really is an interrupt problem, set the IRQ to 0 with "setserial". This will tell the

driver to use polling instead of interrupts. If this seems to fix the "slow" problem then you had an interrupt

problem. You should still try to solve the problem since polling uses excessive computer resources.

Checking to find the interrupt conflict may not be easy since Linux supposedly doesn't permit any interrupt

conflicts and will send you a /dev/ttyS?: Device or resource busy error message if it thinks you are attempting

Serial HOWTO

16.4 Serial Port Can't be Found 60