[console] Add facility for rudimentary keyboard mapping

Allow for remapping of ASCII characters returned by the BIOS, using a
map consisting of (from,to) pairs.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/arch/i386/firmware/pcbios/bios_console.c

 #include <realmode.h>
 #include <ipxe/console.h>
 #include <ipxe/ansiesc.h>
+#include <ipxe/keymap.h>
 
 #define ATTR_BOLD		0x08
 
 	return NULL;
 }
 
+/**
+ * Map a key
+ *
+ * @v character		Character read from console
+ * @ret character	Mapped character
+ */
+static int bios_keymap ( unsigned int character ) {
+	struct key_mapping *mapping;
+
+	for_each_table_entry ( mapping, KEYMAP ) {
+		if ( mapping->from == character )
+			return mapping->to;
+	}
+	return character;
+}
+
 /**
  * Get character from BIOS console
  *
 			       : "=a" ( keypress ) : "a" ( 0x1000 ) );
 	character = ( keypress & 0xff );
 
-	/* If it's a normal character, just return it */
+	/* If it's a normal character, just map and return it */
 	if ( character && ( character < 0x80 ) )
-		return character;
+		return bios_keymap ( character );
 
 	/* Otherwise, check for a special key that we know about */
 	if ( ( ansi_seq = scancode_to_ansi_seq ( keypress >> 8 ) ) ) {

src/include/ipxe/keymap.h

+#ifndef _IPXE_KEYMAP_H
+#define _IPXE_KEYMAP_H
+
+/**
+ * @file
+ *
+ * Keyboard mappings
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <ipxe/tables.h>
+
+/** A keyboard mapping */
+struct key_mapping {
+	/** Character read from keyboard */
+	uint8_t from;
+	/** Character to be used instead */
+	uint8_t to;
+} __attribute__ (( packed ));
+
+/** Keyboard mapping table */
+#define KEYMAP __table ( struct key_mapping, "keymap" )
+
+/** Define a keyboard mapping */
+#define __keymap __table_entry ( KEYMAP, 01 )
+
+#endif /* _IPXE_KEYMAP_H */