hd44780/serial: Add support for adjustable backlight. Solve some possible

problems that may arise by comparing signed and unsigned char values.

ChangeLog

@@ -28,6 +28,7 @@ v0.5dev (ongoing development)
  + hd44780: Added 'usb4all' connection type (T. Mohaupt)
  * Fix RPM init script hanging on recent OS (#3488223)
  * lcdproc client: Fix build on OpenBSD >= 5.0
+ * hd44780/serial: Add support for adjustable backlight
 
 v0.5.5
  + sed1330 driver: Add support for HG25504 (L. Lagendijk)

server/drivers/hd44780-serial.c

@@ -304,17 +304,26 @@ serial_HD44780_backlight(PrivateData *p, unsigned char state)
 {
 	unsigned char send;
 
-	if (SERIAL_IF.backlight) {
+	/* If backlight available and escape sequence defined send it */
-		if (SERIAL_IF.backlight_escape) {
+	if (SERIAL_IF.backlight && SERIAL_IF.backlight_escape) {
-			send = SERIAL_IF.backlight_escape;
+		send = SERIAL_IF.backlight_escape;
-			write(p->fd, &send, 1);
+		write(p->fd, &send, 1);
-		}
+	}
+
+	if (SERIAL_IF.backlight == 1) {	/* Backlight is just switchable */
 		if (state == BACKLIGHT_ON)
 			send = SERIAL_IF.backlight_on;
 		else
 			send = SERIAL_IF.backlight_off;
 		write(p->fd, &send, 1);
 	}
+	else if (SERIAL_IF.backlight == 2) {	/* Backlight is adjustable */
+		int val = (state == BACKLIGHT_ON) ? p->brightness : p->offbrightness;
+
+		/* Map the value to output range (rounding up) */
+		send = (val * (SERIAL_IF.backlight_on - SERIAL_IF.backlight_off) + 999) / 1000 + SERIAL_IF.backlight_off;;
+		write(p->fd, &send, 1);
+	}
 }
 
 
@@ -330,7 +339,7 @@ serial_HD44780_scankeypad(PrivateData *p)
 	char hangcheck = 100;
 
 	read(p->fd, &buffer, 1);
-	if (buffer == (SERIAL_IF.keypad_escape & 0xFF)) {
+	if (buffer == SERIAL_IF.keypad_escape) {
 		while (hangcheck > 0) {
 			/* Check if I can read another byte */
 			if (read(p->fd, &buffer, 1) == 1) {

server/drivers/hd44780-serial.h

@@ -9,29 +9,55 @@
 #define SERIALIF_NAME_LENGTH 20
 #define DEFAULT_DEVICE       "/dev/lcd"
 
-/** Declares one configuration enty in the serial_interfaces table */
+/** Declares one configuration entry in the serial_interfaces table */
 struct hd44780_SerialInterface {
-	int          connectiontype;	/**< Connection type from hd44780 config */
+	int           connectiontype;	/**< Connection type from hd44780 config */
-	/** Command escape character. This is always sent, even if 0x00 */
+
-	char         instruction_escape;
+	/** \name Instruction / data escape sequence
-	/** Data escape character. Only sent if not NUL data is within range
+	 * Determines if escape characters have to be sent for instruction or
-	 * configure by data_escape_min and data_escape_max. */
+	 * data values. The instruction escape character is always sent, even
-	char         data_escape;
+	 * if its value is 0x00. The data escape character is only sent it it
-	char         data_escape_min;	/**< Escaped data lower limit (inclusive) */
+	 * is not NUL and data is within range set by data_escape_min and
-	char         data_escape_max;	/**< Escaped data upper limit (exclusive) */
+	 * data_escape_max.
-	unsigned int default_bitrate;	/**< Bitrate device is set to by default */
+	 *@{*/
-	char         if_bits;		/**< Initialize to 8 or 4 bit interface */
+	unsigned char instruction_escape;	/**< Instruction escape character. */
-	char         keypad;		/**< Flag: keypad available */
+	unsigned char data_escape;	/**< Data escape character. */
-	char         keypad_escape;	/**< Keys are escaped with this character */
+	unsigned char data_escape_min;	/**< Escaped data lower limit (inclusive) */
-	char         backlight;		/**< Flag: backlight available */
+	unsigned char data_escape_max;	/**< Escaped data upper limit (exclusive) */
-	/** Escape character to send to indicate a backlight state change */
+	/**@}*/
-	char         backlight_escape;
+
-	char         backlight_off;	/**< Character sent to set display off */
+	unsigned int  default_bitrate;	/**< Bitrate device is set to by default */
-	char         backlight_on;	/**< Character sent to set display on */
+	char          if_bits;		/**< Initialize to 8 or 4 bit interface */
+
+	/** \name Keypad settings
+	 *@{*/
+	char          keypad;		/**< Flag: keypad available */
+	unsigned char keypad_escape;	/**< Keys are escaped with this character */
+	/**@}*/
+
+	/** \name Backlight options
+	 * The backlight flag determines the type of backlight available.
+	 * If the backlight is just switchable, the backlight_off or
+	 * backlight_on characters are sent according to backlight state.
+	 * If the backlight is switchable, these characters must define a range
+	 * of values that are understood as different brightness levels by
+	 * the display. The 'brightness' and 'offbrightness' values from config
+	 * are used according to the backlight state and mapped to this range.
+	 *@{*/
+	char          backlight;	/**< Flag: backlight available
+					 * 0 = none, 1 = switchable, 2 = adjustable */
+	unsigned char backlight_escape;	/**< Escape character to send to indicate
+					 * a backlight state change */
+	unsigned char backlight_off;	/**< Character sent to set display off
+					 * or minimum value if adjustable */
+	unsigned char backlight_on;	/**< Character sent to set display on
+					 * or maximum value if adjustable */
+	/**@}*/
+
 	/** Flag: Device has multiple controllers. If enabled, the displayID
-	 * is added to data escape */
+	 * is added to data_escape and it is always sent. */
-	char         multiple_displays;
+	char          multiple_displays;
-	char         end_code;         /**< Code to send on shutdown */
+	unsigned char end_code;         /**< Code to send on shutdown */
 };
 
 /**