添加rtthread相关代码

riscv/rtthread/components/drivers/cputime/cputime_riscv.c

@@ -0,0 +1,37 @@
+#include <rthw.h>
+#include <rtdevice.h>
+#include <rtthread.h>
+
+#include <board.h>
+
+/* Use Cycle counter of Data Watchpoint and Trace Register for CPU time */
+
+static uint64_t riscv_cputime_getres(void)
+{
+    uint64_t ret = 1000UL * 1000 * 1000;
+
+    ret = (ret * (1000UL * 1000)) / CPUTIME_TIMER_FREQ;
+    return ret;
+}
+
+static uint64_t riscv_cputime_gettime(void)
+{
+    uint64_t time_elapsed;
+    __asm__ __volatile__(
+        "rdtime %0"
+        : "=r"(time_elapsed));
+    return time_elapsed;
+}
+
+const static struct rt_clock_cputime_ops _riscv_ops =
+{
+    riscv_cputime_getres,
+    riscv_cputime_gettime
+};
+
+int riscv_cputime_init(void)
+{
+    clock_cpu_setops(&_riscv_ops);
+    return 0;
+}
+INIT_BOARD_EXPORT(riscv_cputime_init);