cpu/fe310: add RISC-V cpu FE310

New CPU FE310 from SiFive based on RISC-V architecture

build: add makefile for RISC-V builds

Makefile for builds using RISC-V tools

cpu/fe310/Makefile

@@ -0,0 +1,7 @@
+# define the module that is built
+MODULE = cpu
+
+# add a list of subdirectories, that should also be built
+DIRS = periph nano vendor
+
+include $(RIOTBASE)/Makefile.base

cpu/fe310/Makefile.dep

@@ -0,0 +1,3 @@
+ifneq (,$(filter periph_rtc,$(USEMODULE)))
+  USEMODULE += periph_rtt
+endif

cpu/fe310/Makefile.features

@@ -0,0 +1,2 @@
+FEATURES_PROVIDED += periph_cpuid
+FEATURES_PROVIDED += periph_pm

cpu/fe310/Makefile.include

@@ -0,0 +1,10 @@
+
+USEMODULE += newlib_nano
+
+USEMODULE += newlib_syscalls_fe310
+USEMODULE += sifive_drivers_fe310
+
+USEMODULE += periph
+USEMODULE += periph_pm
+
+include $(RIOTMAKE)/arch/riscv.inc.mk

cpu/fe310/context_frame.c

@@ -0,0 +1,83 @@
+
+/*
+ * Copyright (C) 2017 JP Bonn
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     cpu_fe310
+ * @ingroup     cpu
+ * @{
+ *
+ * @file
+ * @brief       compile-time check of context_switch_frame offsets
+ *
+ * @author      JP Bonn
+ * @}
+ */
+
+#include "context_frame.h"
+#include "thread.h"
+
+
+#define CHECK_OFFSET(member)     \
+    _Static_assert(offsetof(struct context_switch_frame, member) == member ## _OFFSET, \
+                   "context_switch_frame offset mismatch for offset member");
+
+static void check_context_switch_frame_alignment(void) __attribute__ ((unused));
+
+/**
+ * @brief   Check size and offsets of context_switch_frame
+ *
+ * This does nothing at runtime.  It is optimized out since it's only
+ * doing compile-time checks.
+ */
+static void check_context_switch_frame_alignment(void)
+{
+    _Static_assert(sizeof(struct context_switch_frame) % 16 == 0,
+                   "Stack pointer should be 16 byte aligned");
+    _Static_assert(sizeof(struct context_switch_frame) == CONTEXT_FRAME_SIZE,
+                   "context_switch_frame size mismatch");
+    CHECK_OFFSET(filler0);
+    CHECK_OFFSET(filler1);
+    CHECK_OFFSET(pc);
+    CHECK_OFFSET(s0);
+    CHECK_OFFSET(s1);
+    CHECK_OFFSET(s2);
+    CHECK_OFFSET(s3);
+    CHECK_OFFSET(s4);
+    CHECK_OFFSET(s5);
+    CHECK_OFFSET(s6);
+    CHECK_OFFSET(s7);
+    CHECK_OFFSET(s8);
+    CHECK_OFFSET(s9);
+    CHECK_OFFSET(s10);
+    CHECK_OFFSET(s11);
+    CHECK_OFFSET(ra);
+    CHECK_OFFSET(tp);
+    CHECK_OFFSET(t0);
+    CHECK_OFFSET(t1);
+    CHECK_OFFSET(t2);
+    CHECK_OFFSET(t3);
+    CHECK_OFFSET(t4);
+    CHECK_OFFSET(t5);
+    CHECK_OFFSET(t6);
+    CHECK_OFFSET(a0);
+    CHECK_OFFSET(a1);
+    CHECK_OFFSET(a2);
+    CHECK_OFFSET(a3);
+    CHECK_OFFSET(a4);
+    CHECK_OFFSET(a5);
+    CHECK_OFFSET(a6);
+    CHECK_OFFSET(a7);
+
+    /*
+     * also check the SP offset in the _frame structure
+     */
+    _Static_assert( offsetof(struct _thread, sp) == SP_OFFSET_IN_THREAD,
+                    "Offset of SP in _thread mismatch");
+
+}