soc: nuvoton: numaker: add poweroff for m46x

Add support of sys_poweroff API on m46x series.
It could support SPD standby or DPD deep power down mode.

Signed-off-by: cyliang tw <cyliang@nuvoton.com>

soc/nuvoton/numaker/m46x/CMakeLists.txt

@@ -6,4 +6,6 @@ zephyr_sources(soc.c)
 
 zephyr_include_directories(.)
 
+zephyr_library_sources_ifdef(CONFIG_POWEROFF poweroff.c)
+
 set(SOC_LINKER_SCRIPT ${ZEPHYR_BASE}/include/zephyr/arch/arm/cortex_m/scripts/linker.ld CACHE INTERNAL "")

soc/nuvoton/numaker/m46x/Kconfig

@@ -9,6 +9,7 @@ config SOC_SERIES_M46X
 	select CPU_HAS_FPU
 	select CPU_HAS_ARM_MPU
 	select CORTEX_M_SYSTICK if SYS_CLOCK_EXISTS
+	select HAS_POWEROFF
 
 config SOC_M467
 	select HAS_NUMAKER_HAL

soc/nuvoton/numaker/m46x/poweroff.c

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2024 Nuvoton Technology Corporation.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/kernel.h>
+#include <zephyr/devicetree.h>
+#include <zephyr/sys/poweroff.h>
+#include <NuMicro.h>
+
+void z_sys_poweroff(void)
+{
+	SYS_UnlockReg();
+
+	/* Clear all wake-up flag */
+	CLK->PMUSTS |= CLK_PMUSTS_CLRWK_Msk;
+
+	/* Select Power-down mode */
+	CLK_SetPowerDownMode(DT_PROP_OR(DT_NODELABEL(scc), powerdown_mode, CLK_PMUCTL_PDMSEL_SPD));
+
+	/* Enable RTC wake-up */
+	CLK_ENABLE_RTCWK();
+
+	/* Enter to Power-down mode */
+	CLK_PowerDown();
+
+	k_cpu_idle();
+
+	CODE_UNREACHABLE;
+}

soc/nuvoton/numaker/m46x/soc.c

@@ -16,6 +16,9 @@ void z_arm_platform_init(void)
 	/* Unlock protected registers */
 	SYS_UnlockReg();
 
+	/* Release I/O hold status */
+	CLK->IOPDCTL = 1;
+
 	/*
 	 * -------------------
 	 * Init System Clock