Hardware Access

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This page is the start of a tutorial about accessing hardware devices on Lazarus. These devices include, but are not limited to: ISA, PCI, USB, parallel port, serial port.

Uniform multi-platform access to hardware devices is not implemented by Free Pascal Runtime Library or by the LCL. So this tutorial will basically cover hardware access methods on different platforms. The code can be compiled on different environments using conditional compiles, like this:

  Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs, ExtCtrls,
 {$IFDEF Unix}

It is not known yet, at this time, if Mac OS X/x86 will allow HW access. It can disallow it, though I assume in that case, in time, drivers like io.dll will appear.

Parallel and Serial Comparison

ISA Cards, PCI Cards and the Parallel Port communicate with the computer using a parallel protocol. The Serial Port and USB devices work with a serial protocol. Because the processor and thus programming languages all work on a parallel approach to data, access to this kinds of protocols is easier to be implemented on the software side. When you access an Integer variable, for example, you can access it's value with a single command. With a serial protocol, however, you can only know one bit at a time, and you need to glue the pieces together to understand the data.

Serial communication is difficult to be implemented directly, but it can be pretty easy if you use a pre-made component. It is also harder on the hardware side, so many devices use specialised Integrated Circuits or even Microcontrolers to implement it.

Now a brief comparison of hardware access protocols will be given:

Speed Hardware implementation difficulty
Serial Port Very slow (< E5 bit/s) Medium
Parallel Port Slow (~ E6 bit/s) Easy
ISA Card Medium (~ E7 bit/s) Medium
USB Medium (~ E7 bit/s) Hard
PCI Card Very Fast (> E9 bit/s) Very Hard

Parallel Communication

Using inpout32.dll for Windows

Windows has different ways to access hardware devices on the 9x series and on the NT series. On the 9x series (95, 98, Me) programs can access the hardware directly, just like they did on DOS. The NT series (Windows NT and XP), however, don't allow this approach. On this architecture, all communication with hardware ports must be through a device driver. This is a security mechanism, but developing a driver can cost too much in terms of time and money for small projects.

Happily there is a library that solves this problem. If Windows NT is detected, it decompresses HWInterface.sys kernel device driver and installs it. If Windows 9x is detected, it simply uses assembler opcodes to access the hardware.

But how do I use the library? Simple! It has only two functions, Inp32 and Out32, and their use is quite intuitive.

We will load the library dynamically, so let's define both functions first:

   TInp32 = function(Address: SmallInt): SmallInt; stdcall;
   TOut32 = procedure(Address: SmallInt; Data: SmallInt); stdcall;
  • Address represents the address of the port you desire to access
  • Out32 sends Data to the port you specify by Address
  • Inp32 returns a byte from the port you specify by Address

Now we can load the library. This can be implemented in a place like the OnCreate method of your program's main form:

   TMyForm = class(TForm)
     { private declarations }
     Inpout32: THandle;
     Inp32: TInp32;
     Out32: TOut32;
 procedure TMyForm.FormCreate(Sender: TObject);
   Inpout32 := LoadLibrary('inpout32.dll');
   if (Inpout32 <> 0) then
     // needs overtyping, plain Delphi's @Inp32 = GetProc... leads to compile errors
     Inp32 := TInp32(GetProcAddress(Inpout32, 'Inp32'));
     if (@Inp32 = nil) then Caption := 'Error';
     Out32 := TOut32(GetProcAddress(Inpout32, 'Out32'));
     if (@Out32 = nil) then Caption := 'Error';
   else Caption := 'Error';

If you load the library on OnCreate just don't forget to unload it in OnDestroy:

 procedure TMyForm.FormDestroy(Sender: TObject);

Here is a simple example of how to use Inp32 function:

   myLabel.Caption := IntToStr(Inp32($0220));

This code was tested with a custom ISA card on port $0220, using Lazarus 0.9.10 on Windows XP. Of course you will need to have Windows on your uses clause in order for this code to run. For deployment you only need to include "inpout32.dll" in the same directory of our application.

This is the homepage for the library: www.logix4u.net/inpout32.htm *see discussion*

Using assembler on Windows 9x

On Windows 9x you can also use assembler code. Suppose you wish to write $CC to the $320 port. The following code will do it:

        movl $0x320, %edx
        movb $0xCC, %al
        outb %al, %dx
    end ['EAX','EDX'];

Troubleshooting on Windows

One possible source of trouble using parallel hardware that does not support Plug And Play on Windows is that Windows may assign the port utilized by your hardware to another device. You can find instructions on the URL below about how to tell Windows not to assign the address of your device to Plug And Play devices:


Using ioperm to access ports on Linux

The best way to access the hardware on Linux is through device drivers, but, due to the complexity of the task of creating a driver, sometimes a quick method is very useful.

In order to use the "ports" unit under Linux your program must be run as root, and IOPerm must be called to set appropriate permissions on the port access. You can find documentation about the "ports" unit here.

The first thing to do is link to (g)libc and call IOPerm. A unit that links to the entire (g)libc exists on free pascal, but this unit gives problems when used directly by application and linking statically to the entire (g)libc library is not a very good idea because it changes often between version in an incompatible manner. Functions like ioperm, however, are unlikely to change.

 {$IFDEF Linux}
 function ioperm(from: Cardinal; num: Cardinal; turn_on: Integer): Integer; cdecl; external 'libc';
  • "from" represents the first port to be accessed.
  • "num" is the number of ports after the first to be accessed, so ioperm($220, 8, 1) will give access for the program for all ports between and including $220 and $227.

After linking to IOPerm you can port[<Address>] to access the ports.

 {$IFDEF Linux}
   i := ioperm($220, 8, 1);
   port[$220] := $00;
   myLabel.Caption := 'ioperm: ' + IntToStr(i);
   i := Integer(port[$220]);
   myOtherLabel.Caption := 'response: ' + IntToStr(i);

This code was tested with a custom ISA card on port $0220, using Lazarus 0.9.10 on Mandriva Linux 2005 and Damn Small Linux 1.5

General UNIX Hardware Access

{$IFDEF Unix}
Uses Clib;   // retrieve libc library name.

{$IFDEF Unix}
function ioperm(from: Cardinal; num: Cardinal; turn_on: Integer): Integer; cdecl; external clib;

Note that FPC provides an abstraction for ioperm called "fpioperm" in unit x86, and also defines fpIOPL and out-/inport functions. These functions are currently implemented for Linux/x86 and FreeBSD/x86.

It is not recommended to link to libc unless absolutely necessary due to possible deployment and portability functions. Also manual linking to libc (by declaring ad hoc libc imports for functions that are available elsewhere) like done above is not recommended (e.g. the above libc import line will unnecessarily fail if the standard C lib is not called libc, like e.g. libroot on BeOS, or on platforms with a non standard C symbol mangling).

Note 2 Using unit libc is not recommended under any circumstances other than Kylix compatibility. See libc unit

Serial Communication

It is very easy to build a serial communication software using the Synaser library. The example when used together with the Synaser documentation should be trivial to understand. The most important part is TBlockSerial.Config to configure the speed (in bits per second), data bits, parity bits, stop bits and handshake protocol, if any. The following code was tested with a serial mouse connected to COM 1.

program comm;

{$apptype console}

  Classes, SysUtils, Synaser;

  ser: TBlockSerial;
    ser.config(1200, 7, 'N', SB1, False, False);
    while True do
      Write(IntToHex(ser.RecvByte(10000), 2), ' ');

The following code-example is an alternative version of the example above. The example above seems to have a critically fault in its main concept, to be exactly, it is the part with "while true do...". On the Test - System (Asus A6T Laptop with Digitus USB to RS232 Adapter, Ubuntu 8.04.1), this part caused the following error: The application ran only one time successfully per session, when the application was started again, the application was unable to connect to the serial port. Thus, a reboot was necessary everytime the user tried to relaunch the application, which is/was a really annoying bug.

The reason is not difficult to understand: The application is in the while true do - loop, which is, to be more precisely, an endless loop. There is no abort-condition, so the only way to close the application is to close the terminal or to press CTRL-C. But if you quit the application this way, the important part with "ser.free", which frees the serial port, will never be called. This problem is described in the following thread in the German Lazarus-Forum http://www.lazarusforum.de/viewtopic.php?f=10&t=2082

There is a bit code around the main application to make every user clear, not to press CTRL-C. If anyone is worrying, why /dev/ttyUSB0 is used for com-port: this is due to the USB to Serial Adapter (from Digitus) on the test-system. If you have an built-in serial port, please use the 'Com0' - declaration like in the code - example above.

program serialtest;

{$mode objfpc}{$H+}

  {$IFDEF UNIX}{$IFDEF UseCThreads}
  { you can add units after this };

  var l:boolean;

  function check_affirmation():boolean;
  var k:string;
       Writeln('To quit the application please do NOT use CTRL-C! Instead, please press any key to quit the application! '+
       'Please confirm this notification before the application continues! '+
       '[0]=Quit, [1]=Confirm, please continue! ');
       Writeln('Your decision: ');
       if StrtoInt(k) = 1 then
            Writeln('OK, application continues ...');

  procedure RS232_connect;
     ser: TBlockSerial;
          ser.Connect('/dev/ttyUSB0'); //ComPort
          ser.config(1200, 7, 'N', SB1, False, False);
          Write('Device: ' + ser.Device + '   Status: ' + ser.LastErrorDesc +' '+
                Write(IntToHex(ser.RecvByte(10000), 2), ' ');
          until keypressed; //Important!!!
              Writeln('Serial Port will be freed...');
              Writeln('Serial Port was freed successfully!');

     if l=true then
     Writeln('Program quit! ');

Also, the External Links section has UNIX and Windows serial port tutorials.

It is also worth noting the function of the TBlockSerial.LinuxLock parameter under linux. When set to default of True, a connect will try to create a lock file (eg. "LCK..ttyUSB0") under /var/lock and fail if a lock already exists for the requested port. The lock file will be left over if Free was not called. Setting LinuxLock to False will make Synaser ignore port locking.

Alternatives to Synaser:

There is also a Visual component 5dpo that is based in Synaser.

Another very simple fpc Serial unit is now part of freepascal (at least in version 2.2.2), just put Serial in your Uses list however there does not seem to be any documentation other than the Serial.pp source file.



A cross platform possibility for Linux, BSDs and Mac OS X is libusb.

Headers are listed in http://www.freepascal.org/contrib/db.php3?category=Miscellaneous:

name author version date link remarks
libusb.pp Uwe Zimmermann 0.1.12 2006-06-29 http://www.sciencetronics.com/download/fpc_libusb.tgz
libusb.pas Johann Glaser 2005-01-14 http://www.johann-glaser.at/projects/libusb.pas
fpcusb Joe Jared 0.11-14 2006-02-02 http://relays.osirusoft.com/fpcusb.tgz download link broken
libusb.pp Marko Medic 1.0 2010-12-14 http://www.lazarus.freepascal.org/index.php/topic,11435.0.html


If you use one of the chips from FTDI, you can use their pascal headers for their dll interface to the chips.

See also

External Links

  • Communication Protocols speed comparison:
  1. http://en.wikipedia.org/wiki/Serial_port#Speed
  2. http://www.lvr.com/jansfaq.htm - Jan Axelson's Parallel Port FAQ
  3. http://en.wikipedia.org/wiki/USB#Transfer_Speed
  4. http://en.wikipedia.org/wiki/PCI#Conventional_PCI_bus_specifications
  • Serial Communication Links:
  1. On UNIX: [1]
  2. On Windows: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnfiles/html/msdn_serial.asp
  3. Synaser component: http://synapse.ararat.cz/
  4. Comport Delphi package: http://sourceforge.net/projects/comport/