lcdproc/docs/API-v0.5.txt

This document describes the driver API of v0.5 of LCDproc.
At time of this writing, this version is not released and some things might
be changed.

The API consists of several functions to tell the driver that
certains actions should be performed, some data, and several functions
to retrieve configuration data from the server.

OVERVIEW OF OPERATION

The API is best descibed by starting with the struct lcd_logical_driver
which is defined in server/drivers/lcd.h.

The use of the API has changed from v0.4 to v0.5. The default functions that
the server put in the pointers in v0.4 do no longer exist. Instead empty
functions are the default. If a driver implements a function, the function
will be detected by the server. The driver should at least implement all
basic functions like driver_chr and driver_str itself, and should also have
defined a number of other symbols for the server.

I will walk through the driver struct here.


typedef struct lcd_logical_driver {

	//////// Variables in the driver module
	// The driver loader will look for symbols with these names !
	char *api_version;
	int *stay_in_foreground;	// Does this driver require to be in foreground ?
	int *does_input;	// Does this driver do output ?
	int *does_output;	// Does this driver do output ?

The programmer should define the following symbols:
char * api_version = API_VERSION;  // <-- this symbol is defined by make
int stay_in_foreground = 0; // This driver does not need to be in foreground
int does_input = 0;	    // This driver does not do input
int does_output = 1;	    // But only output
And fill these values with the correct values. Upon loading the driver module,
the server will locate these symbols and store pointers to them in the
driver struct.

Because the drivers are loadable, some kind of version checking should be
done. Therefor the server expects the correct version number to be found in
the api_version symbol (a string). For the v0.5 version this should be "0.5".
If the version is incompatible, the driver will not be loaded. The current
API version can always be determined by inserting the compiler define
API_VERSION in the code.



	//////// Functions in the driver module
	// Basic functions

All these Basic functions should be implemented !

	int (*init)		(drvthis, char *args);
	void (*close)		(drvthis);
	int (*width)		(drvthis);
	int (*height)		(drvthis);
	void (*clear)		(drvthis);
	void (*flush)		(drvthis);
	void (*string)		(drvthis, int x, int y, char *str);
	void (*chr)		(drvthis, int x, int y, char c);


	// Extended functions
	void (*vbar)		(drvthis, int x, int y, int len, int promille, int options);
	void (*hbar)		(drvthis, int x, int y, int len, int promille, int options);

These functions have been extended since v0.4. They now now expext complete
coordinates, a length (in chars, not pixels!) a promillage (0 to 1000) and an
option.

	void (*num)		(drvthis, int x, int num);

Draw big numbers on your display. Only 6 positions exist, 1 to 6.
David GLAUDE:
"
I don't think this is valid... There are as many position as wanted.
A BigNum could be at any column from 1 to end of the LCD.
It could also be at -1 and -2 (where only the end is visible).
Optionaly it could be on a specific raw from -3 to end of the LCD.
This permit scrolling of BIGNUM or in the futur BIGFONT.
"

	void (*heartbeat)	(drvthis, int state);

Should be called to animate the heartbeat. The driver should thererfor
probably call the icon function below.

	void (*icon)		(drvthis, int x, int y, int icon);

Tells to place a certain icon at a position.


	// Userdef characters
	void (*set_char)	(drvthis, char ch, char *dat);
	int (*get_free_chars)	(drvthis);
	int (*cellwidth)	(drvthis);
	int (*cellheight)	(drvthis);

Functions to define a character. It is currently unclear how this system
should exactly work. The set_char function expects a simple block of data
with 1 byte for each pixel-line. So that is 8 bytes for a 5x8 char.


	// Hardware functions
	int (*contrast)		(drvthis, int contrast);
	void (*backlight)	(drvthis, int brightness);
	void (*output)		(drvthis, int state);


	// Key functions
	char *(*get_key)	(drvthis);

Returns a string. This string is withing driver's memory space and the server
should therefor never try to modify this string.

	char * (*get_info) ();

Returns a string describing the driver and it's features.



	//////// Variables in server core available for drivers

	char * name;		// Name of this driver.
	void * private_data;

These variables should be taken read-only for the drivers. The name variable
should be used to access the driver's own section in the config file.
The private_data pointer is the pointer to the driver's own data block. This
pointer should be stored using the store_private_ptr function below. The
driver should cast this to it's own private structure pointer.


	//////// Functions in server core available for drivers

	int (*store_private_ptr) (struct lcd_logical_driver * driver, void * private_data);

Store the driver's private data:


	// Config file functions, filled by server
	char (*config_get_bool)	(char * sectionname, char * keyname,
				int skip, char default_value);
	int (*config_get_int)	(char * sectionname, char * keyname,
				int skip, int default_value);
	double (*config_get_float) (char * sectionname, char * keyname,
				int skip, double default_value);
	char *(*config_get_string) (char * sectionname, char * keyname,
				int skip, char * default_value);
				// Returns a string in server memory space.
				// Copy this string.
	int config_has_section	(char *sectionname);
	int config_has_key	(char *sectionname, char *keyname);

See configfile.h on how to use these functions. As sectionname, always use the
driver name: drvthis->name


	// Reporting function
	void (*report)			( const int level, const char *format, .../*args*/ );

Easily usable report functions by including drivers/report.h. See that file
for details.


	// Display properties functions (for drivers that adapt to other loaded drivers)
	int (*get_display_width) ();
	int (*get_display_height) ();

If you have a driver that can adapt its size to the size of an other driver,
it should read these values. If there is no other driver loaded yet, the
returned values will be 0.


	// Driver private data
	void * private_data;	// Filled by server by calling store_private_ptr()

} Driver;

The flush_box and draw_frame functions have been removed for v0.5.



PRIVATE DATA

With the introduction of loadable modules it is necesary to stop using global
variables to store a driver's data in. Instead, you should store it in a
structure, that you allocate abd store on driver's init. If you don't use
this system, but use globals, you get queer results if you run two LCDd
daemons on one machine. They will then use the same variables !

In the driver's private structure will probably at least be something like:

typedef struct my_driver_private {

        // Size in cells of the LCD
        int width, height;
        // Size of each LCD cell, in pixels
        int cellwidth, cellheight;
        // Frame buffer...
        char *framebuf;
} PrivateData;

You allocate and store this structure like this:

	PrivateData * p;

	// Alocate and store private data
	p = (PrivateData *) malloc( sizeof(PrivateData) );
	if( p == NULL )
		return -1;
	if( drvthis->store_private_ptr( drvthis, p ) < 0 )
		return -1;

	(... continue with the rest of your init routine)


You retrieve this private data pointer by adding the following code to the
beginning of your functions:

  PrivateData * p = (PrivateData*) drvthis->private_data;

Then you can access your data like:
  p->framebuf




FUNCTIONS IN DETAIL

int (*init)		(drvthis, char *args);
// The init function
// Starts up the LCD, initializes all vars. Allocates private data space
// and stores the pointer by calling store_private_ptr();

void (*close)		(drvthis);
// Shuts down the connection with the LCD.
// Called just before unloading the driver.

int (*width)		(drvthis);
// Get the screen width.

int (*height)		(drvthis);
// Get the screen height.

void (*clear)		(drvthis);
// Clears the framebuffer

void (*flush)		(drvthis);
// Flushes the framebuffer to the LCD.

void (*string)		(drvthis, int x, int y, char *str);
// Places a string in the framebuffer
// All coordinates are 1-based, (1,1) is top left.
// Driver should check for overflows

void (*chr)		(drvthis, int x, int y, char c);
// Places a char in the framebuffer
// Driver should check for overflows

void (*vbar)		(drvthis, int x, int len);
// Draws a vertical bar at horizontal position x and with length len.
// init_vbar will be called once before this functions.

void (*hbar)		(drvthis, int x, int y, int len);
// Draws a horizontal bar at position x,y and with length len.
// init_hbar will be called once before this functions.

void (*num)		(drvthis, int x, int num);
// Displays a big number at position x.

void (*heartbeat)	(drvthis, int state);
// Sets the heartbeat to the indicated state.
// 0=off 1=graph1 2=graph2
David GLAUDE:
"state is apparently type and it could have the value
HEARTBEAT_ON to say that we want to display/refresh the heartbeat.
The driver choose how to do it. See MtxOrb.c"

int (*contrast)		(drvthis, int contrast);
// Sets the contrast to the given value. Values should be 0 to 255.
// Many displays do not support software setting of contrast.
// Use -1 to get the current value returned.

void (*backlight)	(drvthis, int on);
// Sets the backlight to brightness 'on'.
// Often hardware can only support on and off, in that case any value
// of on>0 will switch the backlight on.

void (*output)		(drvthis, int on);
// Sets the output value. Some displays/wirings have a general purpose
// output, which can be controlled by calling this function. See the
// 'output' command in the 'widget language'.

char *(*getkey) ();
// Checks if a key has been pressed on the device.
// Returns NULL for "no key pressed", or a string describing the pressd key.
// These characters should match the keypad-layout.

char *(*getinfo) ();
// Returns a string describing the driver and its features.


char (*config_get_bool)	(char * sectionname, char * keyname,
			int skip, char default_value);
// Call to server. Retrieve a bool from the config file.
// Sectionname should be the name of the driver (as in the struct).
// If the key cannot be found, the default value will be returned.
// skip should be 0 usually, but if you want to retrieve multiple
// identical keys, then increase skip to get every next value.

int (*config_get_int)	(char * sectionname, char * keyname,
			int skip, int default_value);
// Call to server. Retrieve an integer from the config file.

double (*config_get_float) (char * sectionname, char * keyname,
			int skip, double default_value);
// Call to server. Retrieve a float from the config file.

char *(*config_get_string) (char * sectionname, char * keyname,
			int skip, char * default);
// Call to server. Retrieve a string from the config file.
// Fill result with a pointer to some available space. You can fill it
// with a default value. If the key is found, it will be overwritten
// with the value from the key.
// Note that you should always first copy the the returned string.
// It is in the address space of the server, and will be freed at the
// next call.

int config_has_section	(char *sectionname);
// Returns wether a section exists. Does not need to be called prior
// to a call to a config_get_* function.

int config_has_key	(char *sectionname, char *keyname);
// Returns the number of times a key exists. Does not need to be called
// prior to a call to a config_get_* function.


First version, Joris Robijn, 20011016