Hardware manual

11.1 Serial Monitoring/Diagnostics Programs
A few Linux programs (and one "file") will monitor various modem control lines and indicate if they are
positive (1 or green) or negative (0 or red).
serlook can snoop on serial line traffic (via a wiretap) and also send/receive on a serial line.•
The "file": /proc/tty/driver/serial lists those that are asserted (positive voltage)•
modemstat (Only works correctly on Linux PC consoles.) Status monitored in a tiny window.
Color-coded and compact. Must kill it (a process) to quit.
•
statserial (Info displayed on entire screen)•
serialmon (Doesn't monitor RTS, CTS, DSR but logs other functions)•
As of June 1998, I know of no diagnostic program in Linux for the serial port.
11.2 Changing Interrupt Priority
irqtune will give serial port interrupts higher priority to improve performance.•
hdparm for hard-disk tuning may help some more.•
11.3 What is Setserial ?
This part is in 3 HOWTOs: Modem, Serial, and Text-Terminal. There are some minor differences, depending
on which HOWTO it appears in.
Setserial problems with linmodems, laptops
If you have a Laptop (PCMCIA) don't use setserial until you read Laptops: PCMCIA.
Introduction
setserial is a program used for the user to communicate with the serial device driver. You normally never
need to use it, provided that you only use the one or two serial ports that come as standard equipment with a
PC. Even in other cases, most extra serial ports should be auto-detected by modern kernels. Except you'll need
to use setserial if you have an old ISA serial port set by jumpers on the physical hardware or if your kernel
(such as 2.2 or older) doesn't both detect and set your add-on PCI serial ports.
setserial allows you (or a shell script) to talk to the serial software. But there's also another program,
tt/stty/, that also deals with the serial port and is used for setting the port speed, etc.
setserial deals with the lower-level configuring of the serial port, such as dealing with IRQs (such as 5),
port addresses (such as 3f8), and the like. A major problem with it is that it can't set or configure the serial
port hardware: It can't set the IRQ or port addresses into the hardware. Furthermore, when it seemingly reports
the configuration of the hardware, it's sometimes wrong since it doesn't actually probe the hardware unless
you specifically tell it to. Even then, it doesn't do the modern type of bus probing and some hardware may
never be found by it. Still, what it shows is right most all the time but if you're having trouble getting a serial
port to work, then there's a fair chance it's wrong.
In olden days, when the IRQ and port address was set by jumpers on the serial card, one would use
setserial to tell the driver how these jumpers were set. Today, when plug-and-play methods detect how
Serial HOWTO
11.1 Serial Monitoring/Diagnostics Programs 41