{"id":3120,"date":"2024-10-30T17:08:11","date_gmt":"2024-10-30T17:08:11","guid":{"rendered":"https:\/\/iotthinghub.com\/?p=3120"},"modified":"2024-10-30T17:37:23","modified_gmt":"2024-10-30T17:37:23","slug":"iwdg-wwdg-sensor-checking","status":"publish","type":"post","link":"https:\/\/iotthinghub.com\/?p=3120","title":{"rendered":"IWDG & WWDG : Sensor Checking"},"content":{"rendered":"\n

In ATmel section we learn about watchdog timer. In STm32 we have system window watchdog (WWDG) & independent watchdog (IWDG). Not all STm32 family has IWDG feature but all have WWDG feature. The system window watchdog (WWDG) is used to detect the occurrence of a software fault, usually generated by external interference or by unforeseen logical conditions, which causes the application program to abandon its normal sequence.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

It is basically a window were you have to refresh the counter otherwise the mcu will reset. The formula to calculate the timeout value is given by:<\/p>\n\n\n\n

tWWDG <\/sub>= tPCLK<\/sub> x 4096 x2WDGTB[1:0] <\/sup>x (T[5:0]+1)\u00a0 (ms)<\/p>\n\n\n\n

Here tWWDG<\/sub>: WWDG timeout & TPCLK<\/sub>: APB clock period measured in ms<\/p>\n\n\n\n

As an example, lets assume APB frequency is equal to 48 MHz, WDGTB[1:0] is set to 3 and T[5:0] is set to 63, the window minimum time will be<\/p>\n\n\n\n

            tWWDG <\/sub>= (1\/48000)*4096*23<\/sup>*(63+1) = 43.69ms ~ 43ms<\/p>\n\n\n\n

The maximum window value will be at T = 127 ,<\/p>\n\n\n\n

           tWWDG<\/sub> = (1\/48000)*4096*23<\/sup>*(127+1) ~ 87ms<\/p>\n\n\n\n

Thus if we refresh after 43ms the program will flow otherwise the mcu will reset continuously & the range from 43ms to 87ms. Hall library function to refresh-<\/p>\n\n\n

\nHAL_WWDG_Refresh(&hwwdg);   \/\/ refresh WWDG\n<\/pre><\/div>\n\n\n
IWDG : The devices feature an embedded watchdog peripheral that offers a combination of high safety level, timing accuracy and flexibility of use. The Independent watchdog peripheral detects and solves malfunctions due to software failure, and triggers system reset when the counter reaches a given timeout value.<\/p>\n\n\n\n
The independent watchdog (IWDG) is clocked by its own dedicated low-speed clock (LSI) and thus stays active even if the main clock fails.<\/p>\n\n\n\n
The formula to calculate the timeout value is given by:<\/p>\n\n\n\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 tIWDG<\/sub> = tLSI<\/sub> x 4 x 2PR<\/sup> x (RL +1) <\/p>\n\n\n\n
Where tLSI \u00a0<\/sub>is low-speed clock (LSI) frequency and PR & RL are fields of IWDG registers. In our timer basic section we learn to interface digital temperature sensor DS18B20. Let look at the datasheet of STm mcu, there is a dedicated fLSI <\/sub>= 40kHz. If the prescaler for LSI clock 16, then every counting frequency will be 2.5kHz and time 0.4ms. If we set counting value 212<\/sup> or 4096 then maximum time to reset will be 1.6384s.<\/p>\n\n\n\n
\"\"<\/figure>\n\n\n\n
fLSI   <\/sub>= 40kHz &  prescaler 16 , then new fLSI <\/sub>= 2.5kHz , tLSI <\/sub>= 1\/fLSI<\/sub> = 0.4ms and RL = 4095,<\/p>\n\n\n\n
\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 tIWDG <\/sub>= 0.4ms * (RL+1) \u00a0= 0.4 x 10-3 <\/sup>* (4095+1) = 1.6384s <\/p>\n\n\n\n
If we activate IWDG at prescaler 16, fLSI \u00a0<\/sub>40kHz & counter reload value 4095, then we have 1.6384s to read the sensor data & refresh the counter. If the counter will not refresh within 1.6s the microcontroller halt and restart again & again. Hall library function to refresh-<\/p>\n\n\n
\nHAL_IWDG_Refresh(&hiwdg);  \/\/ refresh IWDG Counter\n<\/pre><\/div>\n\n\n
The other logic will be same in timer section one additional part is to activate IWDG timer with the above parameter. In my example I used I2<\/sup>C1 for OLED & GPIOB-> PINB5 for sensor reading. The main program as follow (only the change parameter)-<\/p>\n\n\n
\n#include "ssd1306.h"\n#include "ds18b20.h"\n  uint8_t temp;\n  char display[16]; \n  init_OLED();\n  clear_display();\n  OLCD_write_string(0,0,"iotthinghub.com");\n  OLCD_write_string(2,0,"Connecting Sen..");\n  HAL_Delay(1000);\n  MX_IWDG_Init();\nwhile (1)\n  {\n      temp=DS18B20ReadTemp();\n      if(temp) HAL_IWDG_Refresh(&hiwdg);\n      else OLCD_write_string(2,0,"Sensor Missing.."); \/\/This line will not execute\n      if(temp) sprintf(display,"Tem:%.4f C   ",temperature);\n      OLCD_write_string(2,0,display);\n  }\n\n<\/pre><\/div>\n\n\n
\"\"<\/figure>\n\n\n\n
Connect as shown in the diagram, if you disconnect the GPIO pin PINB5 the mcu will restart again & again. By modification the program GPIO & \u00a0I2<\/sup>C you can used it in any STm32 microcontroller.<\/p>\n\n\n\n
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download<\/a><\/div>\n<\/div>\n<\/div>\n\n\n\n
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IWDG DS18B20.rar<\/a><\/p>\n<\/div>\n<\/div>\n\n\n\n
<\/p>\n","protected":false},"excerpt":{"rendered":"
In ATmel section we learn about watchdog timer. In STm32 we have system window watchdog (WWDG) & independent watchdog (IWDG). Not all STm32 family has IWDG feature but all have WWDG feature. The system window watchdog (WWDG) is used to detect the occurrence of a software fault, usually generated by external interference or by unforeseen […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[],"class_list":["post-3120","post","type-post","status-publish","format-standard","hentry","category-stm-arm-tutorials"],"_links":{"self":[{"href":"https:\/\/iotthinghub.com\/index.php?rest_route=\/wp\/v2\/posts\/3120","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/iotthinghub.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/iotthinghub.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/iotthinghub.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/iotthinghub.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3120"}],"version-history":[{"count":11,"href":"https:\/\/iotthinghub.com\/index.php?rest_route=\/wp\/v2\/posts\/3120\/revisions"}],"predecessor-version":[{"id":3142,"href":"https:\/\/iotthinghub.com\/index.php?rest_route=\/wp\/v2\/posts\/3120\/revisions\/3142"}],"wp:attachment":[{"href":"https:\/\/iotthinghub.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3120"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/iotthinghub.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3120"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/iotthinghub.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3120"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}