tests: skip arch_nop test when machine timer uses divided sys clock

When the case machine timer clock uses the divided system clock,
k_cycle_get_32() can't measure accurately how many cycles elapsed.

For example, use the value as timer clock obtained by dividing
the system clock by 4.
In this case, measuring a duration with k_cycle_get32() has up to 3
(4-1) cycles systematic error.

To run this test, we need to insert an appropriate of nops
with consideration for the errors.
'nop' can not repeat with for loop.
Must insert as separated statement.
But we don't have a convenient function such as
BOOST_PP_REPEAT in C++.

At this time, Implementing a generic test is a bit difficult.
Skipping this test in the case.

Signed-off-by: TOKITA Hiroshi <[email protected]>

Author: soburi

tests/kernel/common/src/irq_offload.c

@@ -121,6 +121,27 @@ __no_optimization void test_nop(void)
 	/* do 2 nop instructions more to cost cycles */
 	arch_nop();
 	arch_nop();
+#if defined(CONFIG_RISCV_MACHINE_TIMER_SYSTEM_CLOCK_DIVIDER)
+	/* When the case machine timer clock uses the divided system clock,
+	 * k_cycle_get_32() can't measure accurately how many cycles elapsed.
+	 *
+	 * For example, use the value as timer clock obtained by dividing
+	 * the system clock by 4.
+	 * In this case, measuring a duration with k_cycle_get32() has up to 3
+	 * (4-1) cycles systematic error.
+	 *
+	 * To run this test, we need to insert an appropriate of nops
+	 * with consideration for the errors.
+	 * 'nop' can not repeat with for loop.
+	 * Must insert as separated statement.
+	 * But we don't have a convenient function such as
+	 * BOOST_PP_REPEAT in C++.
+	 *
+	 * At this time, Implementing a generic test is a bit difficult.
+	 * Skipping this test in the case.
+	 */
+	ztest_test_skip();
+#endif
 #elif defined(CONFIG_ARMV6_M_ARMV8_M_BASELINE) || \
 	defined(CONFIG_ARMV7_M_ARMV8_M_MAINLINE)
 	/* do 4 nop instructions more to cost cycles */