[console] Support AltGr to access ASCII characters via remapping

Several keyboard layouts define ASCII characters as accessible only
via the AltGr modifier.  Add support for this modifier to ensure that
all ASCII characters are accessible.

Experiments suggest that the BIOS console is likely to fail to
generate ASCII characters when the AltGr key is pressed.  Work around
this limitation by accepting LShift+RShift (which will definitely
produce an ASCII character) as a synonym for AltGr.

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

1 files changed, 36 insertions, 4 deletions

diff --git a/src/util/genkeymap.py b/src/util/genkeymap.py
index d38552eb4..ff5ff0a87 100755
--- a/src/util/genkeymap.py
+++ b/src/util/genkeymap.py
@@ -171,6 +171,11 @@ class KeyLayout(UserDict[KeyModifiers, Sequence[Key]]):
         """Basic shifted keyboard layout"""
         return self[KeyModifiers.SHIFT]
 
+    @property
+    def altgr(self):
+        """AltGr keyboard layout"""
+        return self.get(KeyModifiers.ALTGR, self.unshifted)
+
     @classmethod
     def load(cls, name: str) -> KeyLayout:
         """Load keymap using 'loadkeys -b'"""
@@ -278,6 +283,7 @@ class KeymapKeys(UserDict[str, str]):
                 self.ascii_name(source), self.ascii_name(target)
             )
             for source, target in self.items()
+            if ord(source) & ~BiosKeyLayout.KEY_PSEUDO != ord(target)
         ) + '\t{ 0, 0 }\n}'
 
 
@@ -301,13 +307,12 @@ class Keymap:
         raw = {source: self.target[key.modifiers][key.keycode].ascii
                for source, key in self.source.inverse.items()}
         # Eliminate any null mappings, mappings that attempt to remap
-        # the backspace key, or mappings that would become identity
-        # mappings after clearing the high bit
+        # the backspace key, or identity mappings
         table = {source: target for source, target in raw.items()
                  if target
                  and ord(source) != 0x7f
                  and ord(target) != 0x7f
-                 and ord(source) & ~BiosKeyLayout.KEY_PSEUDO != ord(target)}
+                 and source != target}
         # Recursively delete any mappings that would produce
         # unreachable alphanumerics (e.g. the "il" keymap, which maps
         # away the whole lower-case alphabet)
@@ -327,6 +332,28 @@ class Keymap:
                              (unshifted, shifted))
         return KeymapKeys(dict(sorted(table.items())))
 
+    @property
+    def altgr(self) -> KeymapKeys:
+        """AltGr remapping table"""
+        # Construct raw mapping from source ASCII to target ASCII
+        raw = {source: self.target.altgr[key.keycode].ascii
+               for source, key in self.source.inverse.items()
+               if key.modifiers == KeyModifiers.NONE}
+        # Identify printable keys that are unreachable via the basic map
+        basic = self.basic
+        unmapped = set(x for x in basic.keys()
+                       if x.isascii() and x.isprintable())
+        remapped = set(basic.values())
+        unreachable = unmapped - remapped
+        # Eliminate any null mappings, mappings for unprintable
+        # characters, or mappings for characters that are reachable
+        # via the basic map
+        table = {source: target for source, target in raw.items()
+                 if source.isprintable()
+                 and target
+                 and target in unreachable}
+        return KeymapKeys(dict(sorted(table.items())))
+
     def cname(self, suffix: str) -> str:
         """C variable name"""
         return re.sub(r'\W', '_', (self.name + '_' + suffix))
@@ -336,6 +363,7 @@ class Keymap:
         """Generated source code"""
         keymap_name = self.cname("keymap")
         basic_name = self.cname("basic")
+        altgr_name = self.cname("altgr")
         code = textwrap.dedent(f"""
         /** @file
          *
@@ -352,12 +380,16 @@ class Keymap:
         /** "{self.name}" basic remapping */
         static struct keymap_key {basic_name}[] = %s;
 
+        /** "{self.name}" AltGr remapping */
+        static struct keymap_key {altgr_name}[] = %s;
+
         /** "{self.name}" keyboard map */
         struct keymap {keymap_name} __keymap = {{
         \t.name = "{self.name}",
         \t.basic = {basic_name},
+        \t.altgr = {altgr_name},
         }};
-        """).strip() % self.basic.code
+        """).strip() % (self.basic.code, self.altgr.code)
         return code