Okay, by this stage in your computer technologies career you’re already familiar with the usual litany:
- Check out any POST errors you get,
- Make sure SCSI drives are terminate,
- Make sure it’s plugged in,
- Make sure it’s turned on,
- etc. etc. etc. ….
Things get trickier fast once you reach the stage of checking IRQ and I/O addresses. At this point you must remember one thing:
Log files are the ultimate resource for hardware diagnosis.
Take a good detailed look at what happened during the last boot. Command:
dmesg > lastboot.txt
then:
less lastboot.txt
This gives you a good view into the boot process, in agonizing detail.
You may also have information (or you may not) in /var/log/boot.log. Check it and /var/log/messages, the main system log file.
less /var/log/boot.log
less /var/log/messages
Modems and serial ports look like the same thing to your Linux system. Thus they can sometimes fight for the same IRQs and I/O addresses. Use the setserial command to set IRQ, I/O, and port speed:
setserial /dev/ttyS0 irq 11 port 0x03f8
and check the results:
setserial /dev/ttyS0
The relevant keywords are:
| Option | Purpose |
| port n | Sets I/O address |
| irq n | Sets IRQ to n |
| auto_irq | Tries to detect IRQ setting |
| spd_hi | Sets serial port speed to 56KB/s |
| spd_vhi | Sets serial port speed to 115KB/s |
| spd_normal | Sets serial port speed to 38.4KB/s |