From b22853b2f4bdd1ed31d601ebd331083d67d40f11 Mon Sep 17 00:00:00 2001
From: Palmer Dabbelt <palmer@dabbelt.com>
Date: Tue, 13 Jun 2017 15:14:38 -0700
Subject: 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.
---
 software/smp/Makefile |  6 ++++++
 software/smp/atomic.h | 29 +++++++++++++++++++++++++++++
 software/smp/smp.c    | 40 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)
 create mode 100644 software/smp/Makefile
 create mode 100644 software/smp/atomic.h
 create mode 100644 software/smp/smp.c

(limited to 'software/smp')

diff --git a/software/smp/Makefile b/software/smp/Makefile
new file mode 100644
index 0000000..4131ffc
--- /dev/null
+++ b/software/smp/Makefile
@@ -0,0 +1,6 @@
+TARGET = smp
+C_SRCS += smp.c
+CFLAGS += -O2 -fno-builtin-printf -DENABLE_SMP
+
+BSP_BASE = ../../bsp
+include $(BSP_BASE)/env/common.mk
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
diff --git a/software/smp/smp.c b/software/smp/smp.c
new file mode 100644
index 0000000..36c9db9
--- /dev/null
+++ b/software/smp/smp.c
@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <unistd.h>
+#include "atomic.h"
+void write_hex(int, unsigned long);
+
+atomic_t tty_lock = ATOMIC_INIT(0);
+
+void get_lock(atomic_t *lock)
+{
+  while (atomic_xchg(lock, 1) == 1);
+  mb();
+}
+
+void put_lock(atomic_t *lock)
+{
+  mb();
+  atomic_xchg(lock, 0);
+}
+
+int secondary_main(int hartid)
+{
+  volatile int counter;
+
+  while (1) {
+    get_lock(&tty_lock);
+    write(1, "hello world from hart ", 22);
+    char s[] = {'0', '\n', '\0'};
+    s[0] += hartid;
+    write(1, s, 2);
+    put_lock(&tty_lock);
+
+    for (counter = 0; counter < 10000 + 100*hartid; ++counter)
+        mb();
+  }
+}
+
+int main()
+{
+  return secondary_main(0);
+}
-- 
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