Hardware Access/es

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Overview

Esta página es el comienzo de un tutorial que trata del acceso a dispositivos hardware. Estos dispositivos incluyen entre otros: ISA, PCI, USB, puerto paralelo, puerto serie, etc.

El acceso a dispositivos hardware no esta implementado en la modalidad multiplataforma ni para el Runtime ni para el LCL de Free Pascal, por lo que este tutorial básicamente cubrirá los métodos de acceso a hardware en las diferentes plataformas. El código puede ser compilado en diferentes entornos utilizando compilaciones condicionales, como las siguientes:

uses
 Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs, ExtCtrls,
{$IFDEF WIN32}
  Windows;
{$ENDIF}
{$IFDEF Unix}
  ports;
{$ENDIF}

No se sabe todavía, hasta el momento, si MAC OS X/x86 permitirá el acceso hardware. Puede que lo permita, por lo que puede que con el tiempo aparezcan drivers como io.dll.

Parallel and Serial Comparison

Las tarjetas ISA, PCI y el puerto paralelo se comunican con el ordenador utilizando un protocolo paralelo. El puerto serie y los dispositivos USB en cambio con un protocolo serie. Como tanto el procesador como todos los lenguajes de programación trabajan en una aproximación a datos en paralelo, el acceso a esta clase de protocolos es más fácil de implementar en la parte software. Por ejemplo, cuando se accede a una variable de tipo entero (Integer), es posible acceder a su valor asociado con un simple mandato. Con un protocolo serie, sin embargo, se puede conocer sólamente un bit en cada vez, y se hace necesario unir todos los bits para tener un dato con significado.

La comunicación serie es difícil de implementar directamente, pero puede resultar razonablemente sencillo si se utiliza un componente prediseñado. También se bastante difícil en la parte hardware, por lo que algunos dispositivos utilizan Cirtuitos Integrados especializados o incluso Microcontroladores para implementarlo.

A continuación se presenta una breve comparación de protocolos de acceso a hardware:


Velocidad Dificultad de implementación hardware
Puerto serie Muy lenta (< E5 bit/s) Media
Puerto Paralelo Lenta (~ E6 bit/s) Sencilla
Tarjeta ISA Media (~ E7 bit/s) Media
USB Media (~ E7 bit/s) Laboriosa
Tarjeta PCI Muy rápida (> E9 bit/s) Muy laboriosa

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 throught 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:

type
  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:

type
  TMyForm = class(TForm)
  .........
  private
    { private declarations }
    Inpout32: THandle;
    Inp32: TInp32;
    Out32: TOut32;
  .........
implementation
  .........
procedure TMyForm.FormCreate(Sender: TObject);
begin
{$IFDEF WIN32}
  Inpout32 := LoadLibrary('inpout32.dll');
  if (Inpout32 <> 0) then
  begin
    // needs overtyping, plain Delphi's @Inp32 = GetProc... leads to compile errors
    Inp32 := TInp32(GetProcAddress(Inpout32, 'Inp32'));
    if (@Inp32 = nil) then Caption := 'Error';
    Out32 := TOut32(GetProcAddress(Inpout32, 'Out32'));
    if (@Out32 = nil) then Caption := 'Error';
  end
  else Caption := 'Error';
{$ENDIF}
end;

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

procedure TMyForm.FormDestroy(Sender: TObject);
begin
{$IFDEF WIN32}
  FreeLibrary(Inpout32);
{$ENDIF}
end;

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

{$IFDEF WIN32}
  myLabel.Caption := IntToStr(Inp32($0220));
{$ENDIF}

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:

{$ASMMODE ATT}
...
   asm
       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:

http://support.microsoft.com/kb/135168

Using ioperm to access ports on Linux

The best way to access the hardware on Linux is throught 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.

{$IFDEF Linux}
function ioperm(from: Cardinal; num: Cardinal; turn_on: Integer): Integer; cdecl; external 'libc';
{$ENDIF}

  • "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[$220]);
  myOtherLabel.Caption := 'response: ' + IntToStr(i);
{$ENDIF}

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

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

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


Note that FPC provides an abstraction for ioperm called "fpioperm" in unit x86, and also defines out and 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 compability. This because the unit is relatively unportable (due to excessive exposure of structures and other private symbols) and must only be modified as little as possible out of Kylix compability issues.

Serial Communication

The External Links section has UNIX and Windows serial port tutorials.

USB

libusb

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

FTDI

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

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/

ISA Digital Oscilloscope - A example of hardware access with full source included:

[2]