Hardware manual

Avoiding IO Address Conflicts with Certain Video Boards

The IO address of the IBM 8514 video board (and others) is allegedly 0x?2e8 where ? is 2, 4, 8, or 9. This

may conflict (but shouldn't if the serial port is well designed) with the IO address of ttyS3 at 0x02e8 if the

serial port ignores the leading 0 hex digit when it decodes the address (many do). That is bad news if you try

to use ttyS3 at this IO address. Another story is that Linux will not detect your internal modem on ttyS3

but that you can use setserial to put ttyS3 at this address and the modem will work fine.

IO address conflict with ide2 hard drive

The address of ttyS2 is 3e8-3ef while hard drive ide2 uses 3ee which is in this range. So when booting Linux

you may see a report of this conflict. Most people don't use ide2 (the 3rd hard drive cable) and may ignore this

conflict message. You may have 2 hard drives on ide0 and two more on ide1 so most people don't need ide2.

15.8 Known Defective Hardware

Problem with AMD Elan SC400 CPU (PC-on-a-chip)

This has a race condition between an interrupt and a status register of the UART. An interrupt is issued when

the UART transmitter finishes the transmission of a byte and the UART transmit buffer becomes empty

(waiting for the next byte). But a status register of the UART doesn't get updated fast enough to reflect this.

As a result, the interrupt service routine rapidly checks and determines (erroneously) that nothing has

happened. Thus no byte is sent to the port to be transmitted and the UART transmitter waits in vain for a byte

that never arrives. If the interrupt service routine had waited just a bit longer before checking the status

There is a proposal to fix this by patching the serial driver. But Should linux be patched to accommodate

defective hardware, especially if this patch may impair performance of good hardware?

16. Troubleshooting

See Modem-HOWTO for troubleshooting related to modems or getty for modems. For a Text-Terminal much

of the info here will be of value as well as the troubleshooting info in Text-Terminal-HOWTO.

16.1 Serial Electrical Test Equipment

Breakout Gadgets, etc.

While a multimeter (used as a voltmeter) may be all that you need for just a few serial ports, simple special

test equipment has been made for testing serial port lines. Some are called "breakout ... " where breakout

means to break out conductors from a cable. These gadgets have a couple of connectors which connect to

serial port connectors (either at the ends of serial cables or at the back of a PC). Some have test points for

connecting a voltmeter. Others have LED lamps which light when certain modem control lines are asserted

(turned on). The color of the light may indicate the polarity of the signal (positive or negative voltage). Still

others have jumpers so that you can connect any wire to any wire. Some have switches.

Radio Shack sells (in 2002) a "RS-232 Troubleshooter" (formerly called "RS-232 Line Tester") Cat.

#276-1401. It checks TD, RD, CD, RTS, CTS, DTR, and DSR. A green light means on (+12 v) while red

Serial HOWTO

Avoiding IO Address Conflicts with Certain Video Boards 58