Changes in kernel/arch/arm32/include/asm.h [9d58539:3fa509b] in mainline

File:

• kernel/arch/arm32/include/asm.h (modified) (1 diff)

kernel/arch/arm32/include/asm.h

@@ -43 +43 @@
 #include <trace.h>
 
-/** No such instruction on ARM to sleep CPU. */
+/** CPU specific way to sleep cpu.
+ *
+ * ARMv7 introduced wait for event and wait for interrupt (wfe/wfi).
+ * ARM920T has custom coprocessor action to do the same. See ARM920T Technical
+ * Reference Manual ch 4.9 p. 4-23 (103 in the PDF)
+ * ARM926EJ-S uses the same coprocessor instruction as ARM920T. See ARM926EJ-S
+ * chapter 2.3.8 p.2-22 (52 in the PDF)
+ *
+ * @note Although mcr p15, 0, R0, c7, c0, 4 is defined in ARM Architecture
+ * reference manual for armv4/5 CP15 implementation is mandatory only for
+ * armv6+.
+ */
 NO_TRACE static inline void cpu_sleep(void)
 {
+#ifdef PROCESSOR_ARCH_armv7_a
+        asm volatile ( "wfe" );
+#elif defined(PROCESSOR_ARCH_armv6) | defined(PROCESSOR_arm926ej_s) | defined(PROCESSOR_arm920t)
+        asm volatile ( "mcr p15, 0, R0, c7, c0, 4" );
+#endif
 }