lm4f: Enable FPU using the vector_chipset hook

Newlib and arm-non-eabi-gcc likes to use the FPU by default on
Cortex-M4F chips. AS a result, do the right thing and enable the FPU
by default.

This fixes issues where code is generated which uses the FPU and
causes the CPU to hard-fault. This change removes the responsibility
of FPU initialization from the application code.

This makes the lm4f consistent with other M4+ devices that enable the
FPU in core library startup code.

Signed-off-by: Karl Palsson <karlp@tweak.net.au>

lib/dispatch/vector_chipset.c

@@ -6,6 +6,8 @@
 #	include "../stm32/f7/vector_chipset.c"
 #elif defined(STM32L4)
 #	include "../stm32/l4/vector_chipset.c"
+#elif defined(LM4F)
+#	include "../lm4f/vector_chipset.c"
 #elif defined(LPC43XX_M4)
 #	include "../lpc43xx/m4/vector_chipset.c"
 #elif defined(VF6XX)

lib/lm4f/vector_chipset.c

@@ -0,0 +1,24 @@
+/*
+ * This file is part of the libopencm3 project.
+ *
+ * Copyright (C) 2016 Alexandru Gagniuc <mr.nuke.me@gmail.com>
+ *
+ * This library is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+static void pre_main(void)
+{
+	/* Enable FPU */
+	SCB_CPACR |= SCB_CPACR_FULL * (SCB_CPACR_CP10 | SCB_CPACR_CP11);
+}