Learning curve of FreeRTOS

UM1722 examples

01:Thread Creation example

• The aim of this example is to explain how to create threads using CMSIS-RTOS based on FreeRTOS API. The example implements two threads running with the same priority, which execute in a periodic cycle. Below details about each thread execution. Thread 1: this thread toggles the LED1 each 200 ms for 5 seconds and then it suspends itself, after 5 seconds the thread 2 resume the execution of thread 1 which toggles the LED1each 400 ms for the next 5 seconds

timeline

0s-------------------------------5s----------------------10s-------------------15S

• 0s: Thread 1 toggles LED1 each 200ms;Thread 2 toggles LED1 each 500ms
• 5s:Thread1 suspends itself
• 10s: Thread2 resume thread1; thread2 suspend itself;thread1 LED1 each 400ms
• 15s: thread1 resume thread2; end of the cycle!

02:Semaphores examples

timeline

0s-------------------------------5s----------------------10s

• 0s:Thread1(H) obtains semaphore
• 5s:Thread1 release the semaphore and suspends itself.Thread2 obtains the semaphore,resume Thread1
• 10s:Thread2 release the semaphore,end of cycle

03:SemaphoresISR examples

timeline

0s-------------------------------x-y-z-------------------10s

• 0s:No semaphore,Thread 1 blocked
• x:button click,EXTI ISR created a semaphore
• y:Thread1 unblocked,and get the semaphore
• z:No semaphore again!Thread1 blocked

mutex

1. cubemx

• FreeRTOS configuration->Include parameters->Enable eTaskGetState

timeline

0s-----------a-b-c-d-e-f-g-h-i-j-k-

• 0s:thread1(H) take the mutex,and it calls the delay
• a:thread2(M)found no mutex,blocked
• b:thread3(L)found no mutex,blocked
• c:thread1 release mutex,and suspend itself<-
• d:thread2 take the mutex,and then release the mutex,finally suspend itself
• e:thread3 take the mutex,and then resume thread2
• f:thread2 found no mutex,blocked
• g:thread3 resume thread1
• h:thread1 found no mutex,blocked
• i:thread3 release mutex
• j:thread1 take the mutex,and it calls the delay
• k:thread3 found no mutex,blocked.->

queue

timeline

0s-a-b--------------1s

• 0s:Thread1 put a message then delay
• a:Thread2 get the message
• b:Thread2 try to get the message again,but no message,then blocked
• 1s:Thread1 put a message then delay.end of cycle

timer

1. cubemx

• FreeRTOS configuration->Config parameters->Enable USE_TIMER
• create a timer

timeline

startup---x-------

• startup:initiate the timer then strart the timer
• x:timer is using osWaitUntil() blink every 200ms

LowPower

1. cubemx

• set all free pins as analog(to optimize the power consumption)

2. add some code to configFreeRTOS.h

#if configUSE_TICKLESS_IDLE == 1 
#define configPRE_SLEEP_PROCESSING                        PreSleepProcessing
#define configPOST_SLEEP_PROCESSING                       PostSleepProcessing
#endif /* configUSE_TICKLESS_IDLE == 1 */

every tick,mcu will wakeup,if no intend task need to do,it will sleep again.otherwise,It won't sleep till next tick!