[stm32] internal independent watchdog iwdg

The watchdog should be familiar to everyone ,STM32 There are two kinds of independent watchdog and window watchdog inside ; The independent watchdog depends on the internal crystal LSI Work on , The window watchdog depends on the system clock ;

 The role of the watchdog , Prevent the program from running and cannot realize self reset ; If there is no watchdog , The program is down , May need to go to MCU Power on , Power on again to continue working , thus it can be seen , The watchdog plays an important role in a system .

 Easy to operate , Reduce the reload value to 0 Before , Reload the register value , Let the register value always be greater than 0;

1、 Introduction to working principle

When passing through the key register (IWDG_KR) Write the value 0xCCCC When starting the independent watchdog , The counter starts from reset value 0xFFF Decrement count . When the counter reaches the final value (0x000) It will generate a reset signal （IWDG Reset ）. Any time will keyword 0xAAAA writes IWWDG_KR In the register ,IWDG_RLR The value of will be overloaded into the meter The counter , So as to avoid the reset of watchdog .

2、 Dog feeding cycle range

3、 Design thinking , Why online debugging MCU when ,MCU Not reset ？

IWDG： Overload register (IWDG_RLR) The reload value is not reduced to 0;

Extend a topic ： External watchdog , How to ensure no reset during debugging ？

have access to Jlink hold RST The level of is stable , Don't let the watchdog chip pull down RST level ;

4、IWDG Common problems caused

Inside FLASH The erasure cycle is greater than IWDG Dog feeding cycle ;

Because inside FLASH In operation , Is to use the bus to operate registers , The bus is in the occupied state , At the completion of FLASH Before command operation , Can't do anything , As a result, the dog feeding signal cannot be sent , Dog feeding timeout ,MCU Reset ; I suffered this loss in those years , Mainly aimed at 128KB For sector block erasure , Probably need 800ms;IWDG The cycle is best set at 1S above ;

External watchdog 1.6S cycle , There is no such problem .
Welcome to WeChat official account. , More original works are waiting for you .