diff -Naurp gcc/config/avr/avr-devices.c gcc/config/avr/avr-devices.c
--- gcc/config/avr/avr-devices.c	2011-10-28 12:15:49.000000000 +0530
+++ gcc/config/avr/avr-devices.c	2011-10-28 14:31:05.000000000 +0530
@@ -275,6 +275,7 @@ const struct mcu_type_s avr_mcu_types[] 
   { "avrxmega4",    ARCH_AVRXMEGA4, NULL,                           0, 0x2000, "x64d3" },
   { "atxmega64a3",  ARCH_AVRXMEGA4, "__AVR_ATxmega64A3__",          0, 0x2000, "x64a3" },
   { "atxmega64a3u", ARCH_AVRXMEGA4, "__AVR_ATxmega64A3U__",         0, 0x2000, "x64a3u"},
+  { "atxmega64b3",  ARCH_AVRXMEGA4, "__AVR_ATxmega64B3__",          0, 0x2000, "x64b3"},
   { "atxmega64d3",  ARCH_AVRXMEGA4, "__AVR_ATxmega64D3__",          0, 0x2000, "x64d3" },
   { "atxmega64d4",  ARCH_AVRXMEGA4, "__AVR_ATxmega64D4__",          0, 0x2000, "x64d4" },
     /* Xmega, > 64K, <= 128K FLASH, > 64K RAM.  */
@@ -286,6 +287,7 @@ const struct mcu_type_s avr_mcu_types[] 
   { "atxmega128a3", ARCH_AVRXMEGA6, "__AVR_ATxmega128A3__",         0, 0x2000, "x128a3" },
   { "atxmega128a3u",ARCH_AVRXMEGA6, "__AVR_ATxmega128A3U__",        0, 0x2000, "x128a3u"},
   { "atxmega128b1", ARCH_AVRXMEGA6, "__AVR_ATxmega128B1__",         0, 0x2000, "x128b1" },
+  { "atxmega128b3", ARCH_AVRXMEGA6, "__AVR_ATxmega128B3__",         0, 0x2000, "x128b3" },
   { "atxmega128d3", ARCH_AVRXMEGA6, "__AVR_ATxmega128D3__",         0, 0x2000, "x128d3" },
   { "atxmega192a3", ARCH_AVRXMEGA6, "__AVR_ATxmega192A3__",         0, 0x2000, "x192a3" },
   { "atxmega192a3u",ARCH_AVRXMEGA6, "__AVR_ATxmega192A3U__",        0, 0x2000, "x192a3u"},
diff -Naurp gcc/config/avr/t-avr gcc/config/avr/t-avr
--- gcc/config/avr/t-avr	2011-10-28 12:15:49.000000000 +0530
+++ gcc/config/avr/t-avr	2011-10-28 14:31:05.000000000 +0530
@@ -285,6 +285,7 @@ MULTILIB_MATCHES = \
 	mmcu?avrxmega2=mmcu?atxmega32x1 \
 	mmcu?avrxmega4=mmcu?atxmega64a3 \
 	mmcu?avrxmega4=mmcu?atxmega64a3u \
+	mmcu?avrxmega4=mmcu?atxmega64b3 \
 	mmcu?avrxmega4=mmcu?atxmega64d3 \
 	mmcu?avrxmega4=mmcu?atxmega64d4 \
 	mmcu?avrxmega5=mmcu?atxmega64a1 \
@@ -292,6 +293,7 @@ MULTILIB_MATCHES = \
 	mmcu?avrxmega6=mmcu?atxmega128a3 \
 	mmcu?avrxmega6=mmcu?atxmega128a3u \
 	mmcu?avrxmega6=mmcu?atxmega128b1 \
+	mmcu?avrxmega6=mmcu?atxmega128b3 \
 	mmcu?avrxmega6=mmcu?atxmega128d3 \
 	mmcu?avrxmega6=mmcu?atxmega192a3 \
 	mmcu?avrxmega6=mmcu?atxmega192a3u \