lcdproc/docs/lcdproc-dev/make-driver.docbook

<chapter id="make-driver">
<title>Making a LCDproc driver</title>

<sect1 id="make-driver-intro">
<title>Introduction</title>

<para>
LCDproc is meant to be modular, it is relatively easy to add new input and output drivers to LCDproc. Actually, there are a few things that you can do to make your life easier, they are listed here.
</para>

<para>
This chapter will explain you the major steps and few gotchas of adding your own driver to LCDproc. Enjoy!
</para>

</sect1>

<sect1 id="driver-shared-files">
<title>Shared files specific for drivers</title>

<para>
Driving an LCD display is not easy; you need to address ports, to send bytes in a certain order, to respect timing, and unfortunaly no two operating system let you do this in the same way. But don't dispair! There's hope! Someone in a galaxy far far away, has allready done the dirty job for you! This dirty job has been put in shared files. These shared files are full cross platform and are automagically configured by the configure script. You only need to include them and use their functions to benefit from them.
</para>

<para>
These files are provided only for drivers, others are provided for all of LCDproc. These files are located in the shared directory, they have a dedicated chapter in this book.
</para>

<sect2 id="port.h">
<title>port.h : Parallel port I/O</title>

<para>The file port.h, located in the server/drivers/ directory provide Input/Output and port permissions for the PC compatible parallel port, also known as the LPT port.</para>

<para>
Of course, these functions will only work if the computer where LCDproc runs has parallel port! In these situations, the configure script will see this and disable drivers that need a parallel port.
</para>

<para>port.h file defines 6 static inline functions for port I/O:</para>

<sect3 id="port-in">
<title>Read a byte from port</title>

<funcsynopsis>
<funcprototype>
  <funcdef>static inline int <function>port_in</function></funcdef>
  <paramdef>unsigned short int <parameter>port</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>Returns the content of the byte.</para>

</sect3>
<sect3 id="port-out">
<title>Write a char(byte) 'val' to port</title>

<funcsynopsis>
<funcprototype>
  <funcdef>static inline void <function>port_out</function></funcdef>
  <paramdef>unsigned short int <parameter>port</parameter></paramdef>
  <paramdef>unsigned char <parameter>val</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>Returns nothing (void).</para>

</sect3>
<sect3 id="port-access">
<title>Get access to a specific port</title>

<funcsynopsis>
<funcprototype>
  <funcdef>static inline int <function>port_access</function></funcdef>
  <paramdef>unsigned short int <parameter>port</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>Returns 0 if successful, -1 if failed.</para>


</sect3>
<sect3 id="port-deny">
<title>Close access to a specific port</title>

<funcsynopsis>
<funcprototype>
  <funcdef>static inline int <function>port_deny</function></funcdef>
  <paramdef>unsigned short int <parameter>port</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>Returns 0 if successful, -1 if failed.</para>


</sect3>
<sect3 id="port-access-multiple">
<title>Get access to multiple sequential ports</title>

<funcsynopsis>
<funcprototype>
  <funcdef>static inline int <function>port_access_full</function></funcdef>
  <paramdef>unsigned short int <parameter>port</parameter></paramdef>
  <paramdef>unsigned short int <parameter>count</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>Returns 0 if successful, -1 if failed.</para>

</sect3>
<sect3 id="port-deny-multiple">
<title>Close access to multiple sequential ports</title>

<funcsynopsis>
<funcprototype>
  <funcdef>static inline int <function>port_deny_full</function></funcdef>
  <paramdef>unsigned short int <parameter>port</parameter></paramdef>
  <paramdef>unsigned short int <parameter>count</parameter></paramdef>
</funcprototype>
</funcsynopsis>
<para>Returns 0 if successful, -1 if failed.</para>

</sect3>

<sect3 id="port.h-example">
<title>Example use</title>
<screen>
#include "port.h"

/* Get access to these 3 ports: 
    0x378 (CONTROL), 
    0x379 (STATUS) and 
    0x37A (DATA) 
*/
if ( -1 == port_access_multiple(0x378,3) ) {
	/* Access denied, do something */
}

/* Write a 'A' to the control port */
ort_out(0x378, 'A');

/* Read from the status port */
char status = port_in(0x379);

/* Close the 3 ports */
port_deny_multiple(0x378,3);
</screen>

</sect3>

</sect2>


<sect2 id="adv_bignum.h">
<title>adv_bignum.h : Write Big-Numbers</title>

<para><filename>adv_bignum.h</filename> is the headerfile for <filename>lib_bignum.a</filename> (made from <filename>adv_bignum.c</filename>) which contains everything needed to show big-numbers, including the fonts for the different displays. (All files are located in the <filename>server/drivers/</filename> directory.) </para>
<para/>
<para>There are only a few requirements to the calling driver:</para>
<listitem><para>The displays <replaceable>cellwidth</replaceable> has to be 5 and the <replaceable>cellheight</replaceable> 7 or 8.</para></listitem>
<listitem><para>The following functions have to be implemented: <function> chr( )</function>;
 <function>   set_char( )</function>(only if the display has custom-characters)</para></listitem>
<listitem><para>The custom-characters (if available) have to be at char 0, 1, 2, ..... ,n</para></listitem>
<para/>
<para>The lib determines the correct font, depending on the displaysize and the number of user-character, itself. So it is easy to integrate into the driver.</para>



<sect3 id="adv_bignum.h-usage">
<title>External provided Functions</title>

<funcsynopsis>
<funcprototype>
  <funcdef>void <function>lib_adv_bignum</function></funcdef>
  <paramdef>Driver *<parameter>drvthis</parameter></paramdef>
  <paramdef>int <parameter>x</parameter></paramdef>
  <paramdef>int <parameter>num</parameter></paramdef>
  <paramdef>int <parameter>height</parameter></paramdef>
  <paramdef>int <parameter>do_init</parameter></paramdef>
  <paramdef>int <parameter>customchars</parameter></paramdef>
</funcprototype>
</funcsynopsis>

<para>The main thing the driver has to do is to call this function from its the <function>num( )</function> function.</para>

<para>Where <parameter>num</parameter> is the number (legal: 0,...9,:) to be written, <parameter>height</parameter> the displays hight in characters and <parameter>customchars</parameter> the number of available custom-characters.</para>

<para><parameter>x</parameter> is the x position of the top-left corner of the big-number (the big-numbers don't have a y position). The placing of the characters is done by the client, so the driver only has to forward the position to the lib. The bignumlib has no influence on the placing of the characters.</para>

<para>If <parameter>do_init</parameter> is unequal 0 lib_bignum will set the custom-characters of the display for the big-numbers.</para>
<para>The driver has to check if the custom-characters have to be set or if it is already done and tell it to the lib (using the <parameter>do_init</parameter> parameter).
The common way is to use variable called <replaceable>p-&gt;ccmode</replaceable> or similar. In the different drivers there are some differences in the naming and handling of this variable. So the responsibility of checking and setting is left at the driver.</para>

</sect3>

<sect3 id="adv_bignum.h-intern">
<title>Internal Structure and Functions</title>

<para>The only function of <function>lib_adv_bignum( )</function> is to determine the best display-dependent big-number-function for the given display-parameters, and to call it.</para>
<para/>

<para>The display-dependent functions are named <function>adv_bignum_num_N_M( )</function>.
Where <replaceable>N</replaceable> is the display-hight lines and  <replaceable>M</replaceable> the number of used user-characters.
The bits of the user-characters are stored in <replaceable>static char bignum</replaceable> (take a look at the source and you will see what I mean). (On a display with a <replaceable>cellheight</replaceable> of 7 the lowest line stored is not shown.) While <replaceable>static char num_map</replaceable> defines the placing in the big number. (A big number is always 3 characters wide and 4 characters high. On a big number for 2 line displays the 2 lower lines are not in use.)</para>
<para>If user-characters have to be set the drivers <function>set_char( )</function> function will be called once for every user-character.</para>
<para>Now <function>adv_bignum_write_num( )</function> is called. This function places the 6 or 12 characters the big-number consists of in the framebuffer using the drivers <function>char( )</function> function.</para>

</sect3>

<sect3 id="adv_bignum.h-example">
<title>Example:</title>
<para>Calling the <function>lib_adv_bignum( )</function> from a drivers_num function. (from <filename>serialVFD.c</filename>):</para>
<screen>

MODULE_EXPORT void
serialVFD_num( Driver * drvthis, int x, int num ){
int do_init=0;
PrivateData *p = drvthis-&gt;private_data;


if (p-&gt;ccmode != CCMODE_BIGNUM){ // Are the custom-characters set up correctly? If not:
do_init=1;// Lib_adv_bignum has to set the custom-characters.
p-&gt;ccmode = CCMODE_BIGNUM; // Switch custom-charactermode to bignum.
}
// Lib_adv_bignum does everything needed to show the big-numbers.
lib_adv_bignum(drvthis, x, num, p-&gt;height, do_init, p-&gt;customchars);
}

</screen>

<para>All that's left to do is to include the header-file</para>
<screen>#include "adv_bignum.h"</screen>
<para>and to add <filename>libbignum.a</filename> to the libs and <filename>adv_bignum.h</filename> sources of your driver.</para>


</sect3>

</sect2>

</sect1>

</chapter>