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Hardware Access Using The AmigaBASIC And ARexx Interpreters.
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Part 1.
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(This wil be the FIRST of a number of articles about direct
hardware access using either AmigaBASIC OR ARexx Interpreters.)
Preface:-
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Ever since the birth of the AMIGA, (A1000), it has had some sort of
programming language for YOU to use and write YOUR own experimental
programs with. These languages were issued ~FREE~ as part of the
~Operating System~ so that the likes of yourselves could produce simple
TOOLS and UTILITIES for everyone to use. Eventually other ~FREE~,
~SHAREWARE~ and ~COMMERCIAL~ languages appeared for the AMIGA in ALL
guises and some cracking applications were/are-being developed for
these machines irrespective of how old they are.
There were basically three ~FREE~ languages over the years from year
one of the AMIGAs birth and these were:-
1) MetaComCo's (R), ABasic Interpreter. This was issued in the early
days and will no longer be mentioned again. It is useful for simple
hacks and with the patch supplied on AMINET will work on a standard
A1200(HD).
2) Microsoft's (R), AmigaBASIC Interpreter. This WILL be the interpreter
of choice for any BASIC language coding. It is quite powerful for an
interpreter and IF you have read the article in Issue 45 of......
http://www.thecryptmag.com/
......then you WILL have discovered how to use AmigaBASIC on an
A1200(HD) with KickStart 3.1x... :)
YES!, it is possible, so go to the above site and read the article of
how it is done OR alternatively download the article from:-
http://main.aminet.net/dev/basic/AmigaBASIC-Info.lha
3) ARexx. A derivative of IBM's REXX scripting language, is also quite
powerful although in standard form you can't generate any type of GUI,
(Graphical User Interface), to make your program(s) more user friendly.
This interpreter works with ALL Classic AMIGAs using KickStart 2.0x
and OS 2.0x up to 3.9x. (It is a compromise on the A1 and OS 4.xx+.)
These three ~FREE ISSUE~ interpreters have been part of the AMIGAs
evolution and some interesting programs have been developed using them.
The series of articles over the next few issues of the magazine will be
dedicated to accessing low level HardWare registers to gain access to the
external ports using these two interpreters. There will be NO articles
about specific low level GRAPHICS access as there are numerous amounts
of source code and articles about the subject on AMINET:-
http://main.aminet.net/
(I might include direct sound access, but again, there is a mass of
information about it on AMINET.)
I will be describing how to access the AMIGA NTSC to PAL video change
register first. This is probably the simplest piece of low level hardware
access that does a useful, external, task.
This will be in AmigaBASIC first then ARexx. Have fun and ENJOY simple
solutions to often difficult problems... :)
Enjoy... :)
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WARNING.
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1) DISCONNECT any faulty equipment under test from the MAINS supply.
2) If a DC supply is used do NOT reverse polarity the connections.
3) Do NOT power up any electronic item until it is safe to do so.
4) CHECK and RECHECK all of your construction and repair work thoroughly.
5) Handle ALL tools used with care.
6) Beware of ALL types of solvents, glues and etching fluids.
7) NEVER leave a soldering iron switched on unattended.
8) KEEP everything OUT of the reach of small children.
9) Switch OFF the AMIGA before connecting any hardware.
10) And finally read 1) to 9) again.
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The Back Door:-
---------------
Anyone who knows me also knows my phrases:-
1) There is ALWAYS a back door for YOUR use, programming wise, all you
have to do is find it!. Confessions of a hacker... He he... :)
2) Don't bother to re-invent the wheel AMIGA-WISE as WorkBench has done
ALL of the hard work for you, just use your common sense and exploit
it!. I will describe my TestCardRTG program later in the series.
3) The vast majority of computer users DO-NOT require 32 bit, umpteen
channel 'digital' audio, AND/OR 32 bit, 2560x1600, 240 Hz, Wide Screen
resolutions.
4) Most users are visually impared, that is, they wear some sort of eye
assistance. Therefore the AMIGAs standard resolutions are more than
enough for general developement work.
5) Most people do NOT have perfect stereophonic hearing so the AMIGAs
standard audio facilities are more than enough.
6) As you get older your responses become slower so multi-core CPUs
running at several GHz internal clock-(multiplier) speeds are NOT of
great importance, just, plain old simple usability.
7) Don't worry about notifying the operating system that you want to use
a resource, just grab that resource and use it.
I will be showing you several back doors that I have exploited over the
years and hope that some of YOU readers expand on them and develop your
own ideas for simple add-ons, tools and utilities... :)
FROM NOW ON I WILL ASSUME THAT A STANDARD AMIGA A1200(HD) IS GOING TO BE
USED AND THAT YOU HAVE A COPY OF AmigaBASIC WITH ALL OF THE FD FILES
ALSO. YOU WILL NOT NEED ANY EXTRA REQUIREMENTS, ONLY A FULL INSTALLATION
OF THE RELEVANT AMIGA OPERATING SYSTEM OF YOUR CHOICE. HAVE FUN!!!... :)
All ~register(s)~, ~address(es)~ and ~data~ values will be in decimal
for AmigaBASIC OR hexa-decimal for ARexx and will be for ALL standard
classic AMIGAs. OCS, (Original Chip Set), is also assumed to make
everything backwards compatible... :)
The one exception is below...
From now on......
Set = Logic 0.
Reset = Logic 1.
============================================================================
Let Us Start With The NTSC/PAL Switching Hardware Register:-
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This is the easiest of the direct hardware register accesses. It will
ONLY work on AMIGAs with ECS or AGA chipsets, OCS and RTG will NOT
work!!!. I will assume a standard A600(HD), note that I have deviated
from the standard A1200(HD) also... :)
We will be changing video mode PAL to NTSC and vice versa with a single
BASIC statement. The hardware register to be changed is 14676444 decimal
OR 0xDFF1DC hexadecimal, bit 5. Bit 5 when reset to 1 switches to PAL and
set to 0 switches to NTSC.
CAUTION!!!, ensure that the TV/Monitor attached to the AMIGA can switch
between these two modes.
The AmigaBASIC code will be in OLD-STYLE line number format so people
of all ages can understand it...
REMEMBER MY CRITERIA FROM MAGAZINE ISSUE 44.
I write in what I call ~baby-basic~, that is, I always use the ~LET~
statement to set up variables; also the ~IF.....THEN~ statement(s).
I NEVER use the ~ELSE~ or ~ELSE[ ]IF~ statements as in my opinion it
makes the code more difficult to understand when you are very young.
I do use the ~END[ ]IF~ statement if it is absolutely neccessary though.
AmigaBASIC Code:-
-----------------
10 REM A PAL-NTSC switching program for AmigaBASIC on an A600(HD).
20 REM Public Domain, 2006, from B.Walker, G0LCU.
30 REM Set up a simple screen using AmigaBASIC's default window.
40 REM Bit 5 of register 0xDFF1DC set to 0 switches the video mode
50 REM to NTSC, reset to 1 switches the video mode to PAL.
60 REM Clear the running window.
70 CLS
80 REM Create a simple menu.
90 PRINT
100 PRINT " PAL-NTSC switching demo, press:-"
110 PRINT
120 PRINT " ~P~ or ~p~ for PAL video."
130 PRINT " ~N~ or ~n~ for NTSC video."
140 PRINT
150 PRINT " ~Q~ or ~q~ to Quit."
160 REM This is the main loop.
170 LET a$=INKEY$
180 IF a$="P" OR a$="p" THEN POKE 14676444&,32
190 IF a$="N" OR a$="n" THEN POKE 14676444&,0
200 IF a$="Q" OR a$="q" THEN GOTO 230
210 GOTO 170
220 REM Quit back to workbench.
230 SYSTEM
As can be seen from the above simple BASIC code only one bit of one
address, (register), 14676444 decimal, (00DFF1DC hexadecimal), is
altered. This is bit 5, which when set to 0 enables NTSC and when reset
to 1 switches to PAL and vice versa.
So therefore of the binary byte, bit 5, shown as a *......
Register 14676444, bits 76543210
||||||||
00*00000
|
......above is decimal value 32 -+, which is 2^5, (2x2x2x2x2).
During normal usage this byte is set to decimal 32 for PAL use OR 0
for NTSC use depending on the country. It is set up during bootup.
Therefore so long as you don't change any other bit all will be well.
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ARexx Code:-
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/* Direct HW programming using ARexx; the video mode switch. */
/* Run from a Shell or CLI only, type 'RX Video-Mode.rexx[RETURN/ENTER]' */
/* without the quotes. Bit 5 of register 0xDFF1DC is set to 0 to switch */
/* the video mode to NTSC and reset to 1 to switch the video mode to PAL. */
/* Set up any constants or variables. */
copyright='9'x'$VER: Video-Mode.rexx_Version_1.00.00_20-09-2006_(C)G0LCU.'
/* Use ECHO for ordinary printing to the screen and SAY for printing results. */
DO FOREVER
ECHO 'c'x
SAY copyright
ECHO 'a'x'd'x'9'x'9'x'0) Video mode set to NTSC.'
ECHO '9'x'9'x'1) Video mode set to PAL.'
ECHO 'a'x'd'x'9'x'9'x'2) Quit this program.'
ECHO 'a'x'd'x'9'x'9'x'Type in a number and then press ENTER/RETURN:-'
PULL number
IF number='0' THEN CALL ntsc
IF number='1' THEN CALL pal
IF number='2' THEN CALL getout
END
/* Switch the video mode to NTSC. */
ntsc:
EXPORT('00DFF1DC'x,'00'x,1)
RETURN
/* Switch the video mode to PAL. */
pal:
EXPORT('00DFF1DC'x,'20'x,1)
RETURN
/* Exit the program safely. */
getout:
EXIT(0)
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That's all there is to it. :)
Now go to HW_ACCESS_PART2 and enjoy.
============================================================================
IMPORTANT:-
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The Legal Stuff:-
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These programs are Freeware and no profit will be made from them,
also all of the files must remain unaltered and intact including this
one. The author is not responsible for any damage to, or loss of, or
failure of equipment or data caused in any way by the use of these
programs. There is NO warranty with the use of these software releases
and YOU USE THEM AT YOUR OWN RISK.
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Testing Evaluation:-
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An A1200(HD) in 2MB, 6MB and 10MB modes using trapdoor memory AND/OR
PCMCIA memory expansions. Also tested on an A600(HD) in 2MB and 6MB
modes. All test conditions were/are running STANDARD KS2.0x to 3.1x,
and using standard ~topaz 8~ fonts throughout.
I have no idea what a strange configuration setup will create so refer
to the ~The Legal Stuff~ above.
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Contact:-
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Mr Barry Walker, G0LCU.
Email:- wisecracker@tesco.net
URL:- http://homepages.tesco.net/wisecracker/G0LCU.HTM
Author of the ~TestGear?~ projects in the ~docs/hard~ drawer of AMINET.
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A very useful HardWare related site, (C) Anthony Hoffman, for
modifications, schematics, repairs and the like is:-
http://amiga.serveftp.net/
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| © RIYAN Productions |
