arc: add _tsc_read for 64-bit timestamp

This implementation of _tsc_read returns a 64-bit value that
is derived from the 64-bit tick count multiplied by hwcycles per tick,
and then it adds the current value from the 32-bit timer.
This produces a 64-bit time. There is a bunch of math here, which
could be avoided if the CPU is built with Real-Time-Clock option.
EM Starter Kit SOCs don't have this. I don't think Arduino 101 does
either.

See ZEP-1559

Change-Id: I9f846d170246556ac40fe2f45809e457c6375d8c
Signed-off-by: Chuck Jordan <[email protected]>

Author: cjordan44

arch/arc/core/Makefile

@@ -3,7 +3,7 @@ ccflags-y +=-I$(srctree)/arch/$(ARCH)/include
 
 obj-y += thread.o thread_entry_wrapper.o \
 	cpu_idle.o  fast_irq.o  fatal.o  fault.o  \
-	fault_s.o  irq_manage.o cache.o  \
+	fault_s.o  irq_manage.o cache.o timestamp.o  \
 	isr_wrapper.o  regular_irq.o  swap.o \
 	sys_fatal_error_handler.o
 

arch/arc/core/timestamp.c

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2017 Synopsys, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * @file
+ * @brief Time Stamp API for ARCv2
+ *
+ * Provide 64-bit time stamp API
+ */
+
+#include <kernel.h>
+#include <toolchain.h>
+#include <kernel_structs.h>
+
+extern int64_t _sys_clock_tick_count;
+extern int sys_clock_hw_cycles_per_tick;
+
+/*
+ * @brief Read 64-bit timestamp value
+ *
+ * This function returns a 64-bit bit time stamp value that is clocked
+ * at the same frequency as the CPU.
+ *
+ * @return 64-bit time stamp value
+ */
+uint64_t _tsc_read(void)
+{
+	unsigned int key;
+	uint64_t t;
+	uint32_t count;
+
+	key = irq_lock();
+	t = (uint64_t)_sys_clock_tick_count;
+	count = _arc_v2_aux_reg_read(_ARC_V2_TMR0_COUNT);
+	irq_unlock(key);
+	t *= (uint64_t)sys_clock_hw_cycles_per_tick;
+	t += (uint64_t)count;
+	return t;
+}

include/arch/arc/v2/asm_inline_gcc.h

@@ -21,6 +21,12 @@ extern "C" {
 #include <stdint.h>
 #include <stddef.h>
 
+/**
+ *  @brief read timestamp register (CPU frequency)
+ */
+extern uint64_t _tsc_read(void);
+
+
 /* Implementation of sys_io.h's documented functions */
 
 static ALWAYS_INLINE