Short:    Timer for serial port Carrier Detection
Author:   simon@studio.woden.com (Simon N Goodwin)
Uploader: simon@studio.woden.com (Simon N Goodwin)
Version:  1.3
Type:     dev/basic


OVERVIEW

This simple HiSoft BASIC program from my Amiga Format series 'Banging
The Metal' shows a low-level way to record time spent online, for
communication software like TERM as well as TCP/IP stacks. It works
by reading the standard serial port hardware. Similar hacks are
possible for other interfaces, if you know their port addresses.

There are two versions - the simple one counts in seconds, while the
other counts in traditional Babylonian hours, minutes and seconds ;-)


CAVEATS

Both get confused by signed arithmetic at midnight. They are bare-bones
examples and intended to show how low-level information can be obtained,
not what to do with it, or when it might be useful: typically only on
your own system, for your own purposes - metal bashing is otherwise
rightly disparaged because it leads to unrepresentative and incompatible
software.


OPERATION

The example directly reads a bit in port A on CIAB, so it suits all real
Amigas and accurate emulations - but not clones like Draco that lack CIAs.
Signals are generally 'active low' - so a 0 level on bit 5 of CIAB port A
indicates modem carrier detection, for instance. In assembler you'd write:

	btst	#5,$BFD000
	bne	NoCarrier

The BASIC equivalent is:

	IF PEEK(12570624) AND 32 THEN PRINT "No Carrier"

The example is an elaborated version of this test. Notice that it does
NOT busy-wait - the WAIT command ensures that the majority of CPU time
is made available to other tasks and processes. Hardware PEEKs need not
be system-hostile!


HISTORY

Originally written by Simon N Goodwin (simon@silicon.studio.co.uk) for the
Amiga Format Banging The Metal tutorial, first published May 1999. Aminet
release by mutual agreement of the author and first publisher. No exclusive
rights relate to this example. It may be freely copied only in its entirety.


DIVERSION

When programming the serial or parallel port, utilities like MapDevice may
divert calls  for SER: or PRT: to alternative hardware. Opening the standard
name doesn't necessarily allocate the default hardware. Check this with
another PEEK, using the eponymous command from Aminet/util/cli/PEEK_POKE.lha

	PEEK DEV=serial long 10 string

This returns the name of the /real/ device selected when you open the device
named after DEV= above, such as "pit.device".for Multiface parallel
redirection, or "duart.device" for GVP serial ports.