M487: Fix crash on WDT reset from power-down

targets/TARGET_NUVOTON/TARGET_M480/device/startup_M480.c

@@ -360,18 +360,12 @@ __asm void Reset_Handler_Cascade(void *sp, void *pc)
 
 #elif defined (__GNUC__) || defined (__ICCARM__)
 
-void Reset_Handler(void)
+__attribute__((naked)) void Reset_Handler(void)
 {
-    /* NOTE: In debugger disassembly view, check initial stack cannot be accessed until initial stack pointer has changed to 0x20000200 */
-    __asm volatile (
-        "mov    sp, %0                  \n"
-        "mov    r0, sp                  \n"
-        "mov    r1, %1                  \n"
-        "b     Reset_Handler_Cascade    \n"
-        :                                           /* output operands */
-        : "l"(0x20000200), "l"(&Reset_Handler_1)    /* input operands */
-        : "r0", "r1", "cc"                          /* list of clobbered registers */
-    );
+    __asm("ldr      sp, =0x20000200                                 \n");
+    __asm("mov      r0, sp                                          \n");
+    __asm("ldr      r1, =Reset_Handler_1                            \n");
+    __asm("b        Reset_Handler_Cascade                           \n");
 }
 
 void Reset_Handler_Cascade(void *sp, void *pc)

targets/TARGET_NUVOTON/TARGET_M480/mbed_overrides.c

@@ -16,6 +16,20 @@
 
 #include "analogin_api.h"
 
+void WDT_IRQHandler(void)
+{
+    /* Check WDT interrupt flag */
+    if (WDT_GET_TIMEOUT_INT_FLAG()) {
+        WDT_CLEAR_TIMEOUT_INT_FLAG();
+        WDT_RESET_COUNTER();
+    }
+
+    /* Check WDT wake-up flag */
+    if (WDT_GET_TIMEOUT_WAKEUP_FLAG()) {
+        WDT_CLEAR_TIMEOUT_WAKEUP_FLAG();
+    }
+}
+
 void mbed_sdk_init(void)
 {
     // NOTE: Support singleton semantics to be called from other init functions
@@ -69,4 +83,49 @@ void mbed_sdk_init(void)
 
     /* Lock protected registers */
     SYS_LockReg();
+
+    /* Get around h/w issue with reset from power-down mode
+     *
+     * When UART interrupt enabled and WDT reset from power-down mode, in the next
+     * cycle, UART interrupt keeps breaking in and cannot block unless via NVIC. To
+     * get around it, we make up a signal of WDT wake-up from power-down mode in the
+     * start of boot process on detecting WDT reset.
+     */
+    if (SYS_IS_WDT_RST()) {
+        /* Enable IP module clock */
+        CLK_EnableModuleClock(WDT_MODULE);
+
+        /* Select IP clock source */
+        CLK_SetModuleClock(WDT_MODULE, CLK_CLKSEL1_WDTSEL_LIRC, 0);
+
+        /* The name of symbol WDT_IRQHandler() is mangled in C++ and cannot
+         * override that in startup file in C. Note the NVIC_SetVector call
+         * cannot be left out when WDT_IRQHandler() is redefined in C++ file.
+         *
+         * NVIC_SetVector(WDT_IRQn, (uint32_t) WDT_IRQHandler);
+         */
+        NVIC_EnableIRQ(WDT_IRQn);
+
+        SYS_UnlockReg();
+
+        /* Configure/Enable WDT */
+        WDT->CTL = WDT_TIMEOUT_2POW4 |      // Timeout interval of 2^4 LIRC clocks
+                WDT_CTL_WDTEN_Msk |         // Enable watchdog timer
+                WDT_CTL_INTEN_Msk |         // Enable interrupt
+                WDT_CTL_WKF_Msk |           // Clear wake-up flag
+                WDT_CTL_WKEN_Msk |          // Enable wake-up on timeout
+                WDT_CTL_IF_Msk |            // Clear interrupt flag
+                WDT_CTL_RSTF_Msk |          // Clear reset flag
+                !WDT_CTL_RSTEN_Msk |        // Disable reset
+                WDT_CTL_RSTCNT_Msk;         // Reset up counter
+
+        CLK_PowerDown();
+
+        /* Clear all flags & Disable WDT/INT/WK/RST */
+        WDT->CTL = (WDT_CTL_WKF_Msk | WDT_CTL_IF_Msk | WDT_CTL_RSTF_Msk | WDT_CTL_RSTCNT_Msk);
+
+        NVIC_DisableIRQ(WDT_IRQn);
+
+        SYS_LockReg();
+    }
 }