source: bootcd/isolinux/syslinux-6.03/gpxe/src/core/console.c

#include "stddef.h"
#include "console.h"
#include <gpxe/process.h>
#include <gpxe/nap.h>

/** @file */

FILE_LICENCE ( GPL2_OR_LATER );

/**
 * Write a single character to each console device.
 *
 * @v character         Character to be written
 * @ret None            -
 * @err None            -
 *
 * The character is written out to all enabled console devices, using
 * each device's console_driver::putchar() method.
 *
 */
void putchar ( int character ) {
        struct console_driver *console;

        /* Automatic LF -> CR,LF translation */
        if ( character == '\n' )
                putchar ( '\r' );

        for_each_table_entry ( console, CONSOLES ) {
                if ( ( ! console->disabled ) && console->putchar )
                        console->putchar ( character );
        }
}

/**
 * Check to see if any input is available on any console.
 *
 * @v None              -
 * @ret console         Console device that has input available, if any.
 * @ret NULL            No console device has input available.
 * @err None            -
 *
 * All enabled console devices are checked once for available input
 * using each device's console_driver::iskey() method.  The first
 * console device that has available input will be returned, if any.
 *
 */
static struct console_driver * has_input ( void ) {
        struct console_driver *console;

        for_each_table_entry ( console, CONSOLES ) {
                if ( ( ! console->disabled ) && console->iskey ) {
                        if ( console->iskey () )
                                return console;
                }
        }
        return NULL;
}

/**
 * Read a single character from any console.
 *
 * @v None              -
 * @ret character       Character read from a console.
 * @err None            -
 *
 * A character will be read from the first enabled console device that
 * has input available using that console's console_driver::getchar()
 * method.  If no console has input available to be read, this method
 * will block.  To perform a non-blocking read, use something like
 *
 * @code
 *
 *   int key = iskey() ? getchar() : -1;
 *
 * @endcode
 *
 * The character read will not be echoed back to any console.
 *
 */
int getchar ( void ) {
        struct console_driver *console;
        int character;

        while ( 1 ) {
                console = has_input();
                if ( console && console->getchar ) {
                        character = console->getchar ();
                        break;
                }

                /* Doze for a while (until the next interrupt).  This works
                 * fine, because the keyboard is interrupt-driven, and the
                 * timer interrupt (approx. every 50msec) takes care of the
                 * serial port, which is read by polling.  This reduces the
                 * power dissipation of a modern CPU considerably, and also
                 * makes Etherboot waiting for user interaction waste a lot
                 * less CPU time in a VMware session.
                 */
                cpu_nap();

                /* Keep processing background tasks while we wait for
                 * input.
                 */
                step();
        }

        /* CR -> LF translation */
        if ( character == '\r' )
                character = '\n';

        return character;
}

/** Check for available input on any console.
 *
 * @v None              -
 * @ret True            Input is available on a console
 * @ret False           Input is not available on any console
 * @err None            -
 *
 * All enabled console devices are checked once for available input
 * using each device's console_driver::iskey() method.  If any console
 * device has input available, this call will return True.  If this
 * call returns True, you can then safely call getchar() without
 * blocking.
 *
 */
int iskey ( void ) {
        return has_input() ? 1 : 0;
}