How to change FreeRTOS initial tick count ?

[ClementBSC]

Hello,

I am using the NRF52840 with FreeRTOS and I would like to start the FreeRTOS tick count at a high value for testing purpose.

I have modified the  configINITIAL_TICK_COUNT value in the FreeRTOS.h file with a high value : 0xffffffff  - 0x1e000 = 0xfffe1fff

(0xffffffff correspond to the maximal tick count, TickType_t beeing a uint32_t value)

(0x1e000 = 2*60*1024 is for 2 minuts, configTICK_TATE_HZ value beeing at 1024)

It should start FreeRTOS tick count at 0xfffe1fff and go back to the zero value after 2 minuts (acctually this is what I want to test), but I have an unexpected result when I use the xTaskGetTickCount() function to see the tick count value (now is the value returned by the xTaskGetTickCount function) :

(FreeTROS.h) #define configINITIAL_TICK_COUNT 0

(LOG) now=4000 (4000 = 3*1024 = 3 sec)

--

(FreeTROS.h) #define configINITIAL_TICK_COUNT 0xfffe1fff

now=3119

I wonld expect the now value to be mutch higer than 4000 (about 0xfffe1fff = 4294844415)

Does anyone know where my problem comes frone ?

Thanks a lot,

Clément

[Susheel Nuguru]

This is purely FreeRTOS initialization code. The value you mentioned in configINITIAL_TICK_COUNT  is directly initialized to below in task.c

PRIVILEGED_DATA static volatile TickType_t xTickCount 				= ( TickType_t ) configINITIAL_TICK_COUNT;

The device specific port changes never resets xTickCount, so i am not sure why you are seeing this behavior. 

It would be interesting to know where exactly you are printing these logs? and the code snippets on how you print them.

[ClementBSC]

Thank you for your answer,

I am printing these logs in a thread called after the vTaskStartScheduler(). I was logging my 32bits TickType_t with a %d instead of a %ld, it may resolve a part of the probleme but I am still in trouble:

I am trying to reproduce this error in a simple environment : I am using the NRF52840 dev board and I took the ble_app_hrs_freertos example code from the nrf SDK. I just added my log in a periodically called function:

static void heart_rate_meas_timeout_handler(TimerHandle_t xTimer)

{

TickType_t val;

val = xTaskGetTickCount();

NRF_LOG_INFO("Tick Count : %ld", val);

And I changed the FreeRTOS.h file from the SDK :

#define configINITIAL_TICK_COUNT 0xff000000

I am using CoolTerm (mac) to print my logs and I have the folowing result:

.[1;31mLogs dropped (196).[0m

<info> app: Tick Count : 1289

.[1;31mLogs dropped (196).[0m

<info> app: Tick Count : 1290

.[1;31mLogs dropped (196).[0m

<info> app: Tick Count : 1291

.[1;31mLogs dropped (196).[0m

<info> app: Tick Count : 1291

.[1;31mLogs dropped (196).[0m

<info> app: Tick Count : 1291

.[1;31mLogs dropped (196).[0m

<info> app: Tick Count : 1291

.[1;31mLogs dropped (197).[0m

<info> app: Tick Count : 1291

.[1;31mLogs dropped (198).[0m

<info> app: Tick Count : 1291

.[1;31mLogs dropped (197).[0m

<info> app: Tick Count : 1292

.[1;31mLogs dropped (197).[0m

<info> app: Tick Count : 1911

<info> app: Tick Count : 2784

<info> app: Tick Count : 3796

<info> app: Tick Count : 4793

<info> app: Tick Count : 5784

It seems that the tick count restarts after a while. Do you have an idea of what is happening ?

[Susheel Nuguru]

 you seems to have found a bug in freertos kernel.

in tasks.c-> vTaskStartScheduler() -> TickCount is uncondictionally initiallized to 0 even though it is already initialized correctly to configINITIAL_TICK_COUNT   when created.

So comment out the below line in in tasks.c-> vTaskStartScheduler()

xNextTaskUnblockTime = portMAX_DELAY;
xSchedulerRunning = pdTRUE;

//xTickCount = ( TickType_t ) 0U;   

/* If configGENERATE_RUN_TIME_STATS is defined then the following
macro must be defined to configure the timer/counter used to generate
the run time counter time base. NOTE: If configGENERATE_RUN_TIME_STATS
is set to 0 and the following line fails to build then ensure you do not
have portCONFIGURE_TIMER_FOR_RUN_TIME_STATS() defined in your
FreeRTOSConfig.h file. */
portCONFIGURE_TIMER_FOR_RUN_TIME_STATS();

And everything works as you expect.

[Susheel Nuguru]

also note that RTC1 counter are 24bit registers, your value does not fit in the counter register 

You calculation must be as below

0x00FFFFFF - 0x1e000 = 0xFE1FFF 

This will fit the 24 bit RTC1 counter register

so set 

(FreeTROS.h) #define configINITIAL_TICK_COUNT 0xfe1fff (and not 0xfffe1fff )

if you are testing for the highest possible tick count then i guess your way of testing will not help you much as tick count is 32 bit and RTC1 counter is 24 bit.

[ClementBSC]

I tried to comment the line //xTickCount = ( TickType_t ) 0U;   on task.c, I changed the value of configINITIAL_TICK_COUNT in FreeRTOS.h to a given value and I have the following result:

when configINITIAL_TICK_COUNT=0x0, 0x1, 0x2, ..., 0x7 : the logs works well and the first xTaskGetTickCount gives a value from 3E8 to 3EF.

when configINITIAL_TICK_COUNT=0x8 or higer : there are dropped logs and the xTaskGetTickCount gives a strange value (examples: configINITIAL_TICK_COUNT=0x8 -> xTaskGetTickCount=1005CF0, configINITIAL_TICK_COUNT=0x8000 -> xTaskGetTickCount=0x1005C00, configINITIAL_TICK_COUNT=0x80000 -> xTaskGetTickCount=0x1005A20)

I am still using the NRF52840 dev board and I took the ble_app_hrs_freertos example code from the nrf SDK with the following changes :

main.c

I added a xTeskGetTickCount in a function called periodically:

static void heart_rate_meas_timeout_handler(TimerHandle_t xTimer)

{

TickType_t val;

val = xTaskGetTickCount();

int_to_hex(val);

I added a function to print the xTeskGetTickCount result in hexadecimal:

void int_to_hex(TickType_t decimal){

long long quotient, remainder;

int i, j = 0;

char hexadecimal[100];

quotient = decimal;

while (quotient != 0)

{

remainder = quotient % 16; //step 1

if (remainder < 10)

hexadecimal[j++] = 48 + remainder; //step 2

else

hexadecimal[j++] = 55 + remainder; //step 3

quotient = quotient / 16; //step 4

}

//step 6

for (i = j; i >= 0; i--)

NRF_LOG_INFO("%c", hexadecimal[i]);

}

Do you have any idear of what is happening ? Thanks a lot!