Add a SMP example

This just prints "hello world" on two cores.  It contains an example of
how to initialize a multi-core system using IPIs, and a simple spin
lock.

1 files changed, 29 insertions, 0 deletions

diff --git a/software/smp/atomic.h b/software/smp/atomic.h
new file mode 100644
index 0000000..074c6a2
--- /dev/null
+++ b/software/smp/atomic.h
@@ -0,0 +1,29 @@
+#ifndef SIFIVE_ATOMIC_H
+#define SIFIVE_ATOMIC_H
+
+#define ATOMIC_INIT(x)		\
+	{			\
+		.counter = (x),	\
+	}
+
+typedef struct {
+  int counter;
+} atomic_t;
+
+static inline int atomic_xchg(atomic_t *v, int n)
+{
+  register int c;
+
+  __asm__ __volatile__ (
+    "amoswap.w.aqrl %0, %2, %1"
+    : "=r" (c), "+A" (v->counter)
+    : "r" (n));
+  return c;
+}
+
+static inline void mb(void)
+{
+  __asm__ __volatile__ ("fence");
+}
+
+#endif