nuvoton - M451 Watchdog Timer

Watchdog Timer 特性

• 18 bits 上數的計數器
• 8 selections of timeout interval
• 2^(4 - 18)
• 4 selections of Watchdog reset delay period
• 3 / 18 / 130 / 1026 * TWDT 
• 支援 watchdog timer interrupt
• 支援 watchdog timer reset
• 支援 watchdog wake-up

Watchdog Timer Clock Source

• LXT (32.768 KHz)
• PCLK0 / 2048
• LIRC (10 KHz)

Watchdog Timer Block Diagram

• WDT Time-out interrupt
• WDTEN(WDT_CTL[7]) = 0, enable WDT and start WDT counter.
• 8 Timeout  interval selected by TOUTSEL(WDT_CTL[10:8]).
• WDT time-out set IF(WDT_CTL[3]) = 1, occur the WDT time-out interrupt.
• WDT Wake-up
• Clock source selected to LIRC or LXT
• WKEN(WDT_CTL[4]) enable
• WDT time-out interrupt to wake-up  power-down system and WKF (WDT_CTL[5]) = 1 
• WDT Reset Delay Period and Reset System
• RSTF (WDT_CTL[2]) keep 1 after WDT time-out reset
• RSTCNT (WDT_CTL[0]) to reset 18-bit WDT
• RSTDSEL (WDT_ALTCTL[1:0]) select reset delay
• RSTEN (WDT_CTL[1]) enable WDT reset
• RSTF (WDT_CTL[2]) =1 when WDT reset delay timeout. 

Watchdog Timeout Interval and Reset Timing

• Watchdog Time-out Interval Period - 
• 計數 Watchdog Tick，計數的範圍由 2^4 到 2^18  
• Watchdog Reset Delay Period
• Watchdog 計數到 Timeout 後，可以選擇再經 3 / 18 / 130 / 1026 個 Watchdog Tick 啟動 Watchdog reset ( MCU cold reset )
• Watchdog Reset Period
• Watchdog reset MCU 的時序

Watchdog Timer Coding Flow

• Enable Watchdog timer module

CLK_EnableModuleClock(WDT_MODULE);

• Select Watchdog timer clock source

CLK_SetModuleClock(WDT_MODULE, CLK_CLKSEL1_WDTSEL_LIRC, 0);

• Enable Watchdog timer interrupt

NVIC_EnableIRQ(WDT_IRQn);

• Initialize Watchdog timeout interval periodic (2^14) and 18 Tick for Watchdog reset delay and start watchdog counting

/* Unlock protected registers */
SYS_UnlockReg();
WDT_Open(WDT_TIMEOUT_2POW14, WDT_RESET_DELAY_18CLK, TRUE, TRUE);
/* Lock protected registers */
SYS_LockReg();

• Enable Watchdog interrupt 

/* Unlock protected registers */
SYS_UnlockReg();
WDT_EnableInt();
/* Lock protected registers */
SYS_LockReg();

• Watchdog timer Interrupt Service

void WDT_IRQHandler(void)
{
    if(g_u32WDTINTCounts < 10)
        WDT_RESET_COUNTER();

    if(WDT_GET_TIMEOUT_INT_FLAG() == 1)
    {
        /* Clear WDT time-out interrupt flag */
        WDT_CLEAR_TIMEOUT_INT_FLAG();

        g_u32WDTINTCounts++;
    }
}

範例程式 :

在 FreeRTOS 中，加入一個 Task 來完成 Watchdog 中斷沒有立即完成的工作，平常 Task 位於 Suspend 的狀態，等 Watchdog 計算完成，叫醒 Task 再經數個 Watchdog Clock (N*0.1 second)，就會啟動 Watchdog reset MCU． 

範例程式位於 Github 的 nuvotoon-M451-Sample 的 FreeRTOS-Watchdog-Sample branch

Reference document :

• nuvoton NuMicro-M451-Series-Training-Material
• nuvoton TRM_M451_Series_EN_Rev2.08