# Problem vTaskSuspend and xTaskResumeFromISR **URL:** \ **Category:** Kernel\ **Created:** [May 26, 2008, 4:52am UTC](https://forums.freertos.org/t/problem-vtasksuspend-and-xtaskresumefromisr/3805 "2008-05-26T04:52:38Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [May 26, 2008, 4:52am UTC](https://forums.freertos.org/t/problem-vtasksuspend-and-xtaskresumefromisr/3805/1 "2008-05-26T04:52:38Z")
**[wellingj](https://sourceforge.net/u/wellingj/)** wrote on [Monday, May 26, 2008](https://sourceforge.net/p/freertos/discussion/382005/thread/a89fc636/#04b8): Hi. I’m using gcc version 4.3.0 and FreeRTOS V5.0.0 for reference. I’m trying to use the vTaskSuspend and xTaskResumeFromISR to debug some servo code that I had modified. Theory of operation is that I have a task that does nothing, until all my ticks of my servo code has gone through and I have all the data, then it gets output onto a serial port using some avrlib stuff. The code is below. What boggles me is that I’ve used the vTaskSuspend and xTaskResumeFromISR in this manner for a I2C command processing with FreeRTOS V 4.3 and it worked wonderfully and so I did a direct port. When it didn’t work, meaning the DebugServo task never runs after it’s first suspension, I started throwing in toggles on a led to see where the code was going and where it wasn’t and I’ve marked which calls to LED\_TOGGLE( YELLOW ) don’t work (no flashing light). The only other task running is just changes the servo position ever 50 milliseconds. I’m running this at a really high rate of 1ms ticks, but I don’t think that should be the problem… Any Ideas? /\*! \file servo\_class.c \brief Interrupt-driven RC Servo function library. \*/ //\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* // // File Name    : ‘servo.c’ // Title        : Interrupt-driven RC Servo function library // Author       : Pascal Stang - Copyright (C) 2002 // Modified     : Jesse Welling - Copyright (C) 2008 // Created      : 7/31/2002 // Revised      : 4/02/2008 // Version      : 1.1 // Target MCU   : Atmel AVR Series // Editor Tabs  : 3 spaces = 1 tab // // This code is distributed under the GNU Public License //      which can be found at [http://www.gnu.org/licenses/gpl.txt](http://www.gnu.org/licenses/gpl.txt) // //\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* #include \ #include \ #include "FreeRTOS.h" #include "task.h" #include "semphr.h" #include "…/avrlib/global.h" #include "…/avrlib/uart.h"    // include uart function library #include "…/avrlib/rprintf.h" // include printf function library #include "servo.h" #include "…/Robostix.h" /\*roll over number\*/ #define TOP   ((uint16\_t)40000u) // handy to think with values #define CENTER\_POSITION\_MSX100   1500u #define MIN\_POSITION\_MSX100      1000u #define MAX\_POSITION\_MSX100      2000u // actual raw values #define CENTER\_POSITION\_RAW      (CENTER\_POSITION\_MSX100 \* 2)  // 3000 #define MIN\_POSITION\_RAW         (MIN\_POSITION\_MSX100 \* 2) // 2000 #define MAX\_POSITION\_RAW         (MAX\_POSITION\_MSX100 \* 2) // 4000 /\* Note: Since only 500 millisecondsX100 is between center and min, and likewise center to max, when multiplied \*       by 2 to get the raw value that gives 1000 which then can be used as a signed percentX10 from center. \*       Nifty! But only for 16Mhz clocks \*/ // Global variables // servo channel registers static volatile uint16\_t ServoPosTics; static volatile uint8\_t  ServoChannel; static const uint16\_t ServoPeriodTics = TOP; xTaskHandle ServoDebugTaskHandle; typedef struct {     uint8\_t  chan;    uint16\_t inc;    uint16\_t nxt;    uint16\_t ocval;    uint16\_t srvpos; }TimerDebug\_T; TimerDebug\_T ServoTimerDebugBuffer[3]; // functions static void DebugServo( void \* param); //! initializes software PWM system void servoInit(void) {    uint8\_t channel;       //TODO REMOVE DEBUG    uartInit();    uartSetBaudRate(115200);    rprintfInit(uartSendByte);    // disble the timer3 output compare A interrupt    cbi(ETIMSK, OCIE3A);    /\* setup timer 3     \*     \* TCCR3A Bit 7:6 – COMnA1:0: Compare Output Mode for Channel A     \* TCCR3A Bit 5:4 – COMnB1:0: Compare Output Mode for Channel B     \* TCCR3A Bit 3:2 – COMnC1:0: Compare Output Mode for Channel C     \* TCCR3A Bit 1:0 – WGMn1:0: Waveform Generation Mode     \*     \* TCCR3B Bit 4:3 – WGMn3:2: Waveform Generation Mode     \* TCCR3B Bit 2:0 – CSn2:0: Clock Select     \*     \* TCCR3C Bit 7 – FOCnA: Force Output Compare for Channel A     \* TCCR3C Bit 6 – FOCnB: Force Output Compare for Channel B     \* TCCR3C Bit 5 – FOCnC: Force Output Compare for Channel C     \*     \*/    TCCR3A |= 0x00;    TCCR3B = 0x02;    TCCR3C |= 0x00;    // enable and clear channels    for(channel=0; channel\duty\_raw = CENTER\_POSITION\_RAW;       // set up DDR for each port.       \*DDR(ServoChannels[ServoChannel]-\>port) |= ServoChannels[ServoChannel]-\>pin\_mask;       // turn off current channel to break out of tristate. see page 67 of the data sheet       \*(ServoChannels[ServoChannel]-\>port) &= ~(ServoChannels[ServoChannel]-\>pin\_mask);    }    // set PosTics    ServoPosTics = 0;    // Start at just past the last forcing the intrrupts to start processing the first.    ServoChannel = NumberOfServoChannels + 1;    // set initial interrupt time    uint16\_t OCValue = 0;    // read in current value of output compare register OCR3A    //OCValue = OCR3A;      // read OCR3A    OCValue =  inb(OCR3AL);      // read low byte of OCR3A    OCValue += inb(OCR3AH)\<\<8;   // read high byte of OCR3A    // increment OCR3A value by nextTics    OCValue += ServoPeriodTics;    ServoTimerDebugBuffer[0].ocval = ServoPeriodTics;    ServoTimerDebugBuffer[1].ocval = ServoPeriodTics;    ServoTimerDebugBuffer[2].ocval = ServoPeriodTics;    // set future output compare time to this new value    //OCR3A = OCValue;         // write 16bit    outb(OCR3AH, (OCValue\>\>8));         // write high byte    outb(OCR3AL, (OCValue & 0x00FF));   // write low byte    // enable the timer3 output compare A interrupt    sbi(ETIMSK, OCIE3A); } //! turns off software PWM system void servoOff(void) {    // disable the timer3 output compare A interrupt    cbi(ETIMSK, OCIE3A); } //! set servo position on channel void servoSetPosition(ServoChannel\_T\* this, int16\_t percentX10) {    // input should be between 0 and SERVO\_POSITION\_MAX    uint16\_t pos\_scaled;    percentX10 = MAX(percentX10, -1000);    percentX10 = MIN(percentX10, 1000);       // calculate scaled position    pos\_scaled = (uint16\_t)( percentX10 + CENTER\_POSITION\_RAW);    // set position    servoSetPositionRaw(this, pos\_scaled); } //! get servo position on channel int16\_t servoGetPosition(ServoChannel\_T\* this) {    return ( (int16\_t)servoGetPositionRaw(this) - CENTER\_POSITION\_RAW ); } //! set servo position on channel (raw unscaled format) void servoSetPositionRaw(ServoChannel\_T\* this, uint16\_t position) {    // bind to limits    position = MAX(position, MIN\_POSITION\_RAW);    position = MIN(position, MAX\_POSITION\_RAW);    // set position    this-\>duty\_raw = position;    //TODO REMOVE DEBUG        /\*    rprintfu08(this-\>pin\_mask);    rprintfChar(’@’);    rprintfu08(this-\>port);    rprintfChar(’:’);    rprintfu16(this-\>duty\_raw);    rprintfCRLF();    \*/    } //! get servo position on channel (raw unscaled format) uint16\_t servoGetPositionRaw(ServoChannel\_T\* this) {    return this-\>duty\_raw; } void PrintServoDebug(void) {    {       rprintfu08(ServoTimerDebugBuffer[0].chan);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[0].inc);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[0].ocval);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[0].nxt);       rprintfChar(’ ');       rprintfu16(ServoTimerDebugBuffer[0].srvpos);       rprintfCRLF();    }    {       rprintfu08(ServoTimerDebugBuffer[1].chan);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[1].inc);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[1].ocval);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[1].nxt);       rprintfChar(’ ');       rprintfu16(ServoTimerDebugBuffer[1].srvpos);       rprintfCRLF();    }    {       rprintfu08(ServoTimerDebugBuffer[2].chan);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[2].inc);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[2].ocval);       rprintfChar(’ ‘);       rprintfu16(ServoTimerDebugBuffer[2].nxt);       rprintfChar(’ ');       rprintfu16(ServoTimerDebugBuffer[2].srvpos);       rprintfCRLF();    } } void StartDebugServoTask(void) {    xTaskCreate (DebugServo, "DbSrv", configMINIMAL\_STACK\_SIZE, NULL, ( tskIDLE\_PRIORITY + 2), &ServoDebugTaskHandle); } static void DebugServo( void \* param) {    for(;😉    {       PrintServoDebug();       vTaskSuspend( NULL );       //The toggle does not work here       //LED\_TOGGLE( YELLOW );    } } ISR(TIMER3\_COMPA\_vect) {    uint16\_t nextTics;    // schedule next interrupt    uint16\_t OCValue;    if(ServoChannel \< NumberOfServoChannels)    {       // turn off current channel       \*(ServoChannels[ServoChannel]-\>port) &= ~(ServoChannels[ServoChannel]-\>pin\_mask);    }       // next channel    ServoChannel++;    if(ServoChannel != NumberOfServoChannels)    {       // loop to channel 0 if needed       if(ServoChannel \> NumberOfServoChannels)   ServoChannel = 0;       // turn on new channel       \*(ServoChannels[ServoChannel]-\>port) |= ServoChannels[ServoChannel]-\>pin\_mask;       // schedule turn off time       nextTics = ServoChannels[ServoChannel]-\>duty\_raw;    }    else //(Channel == NumberOfServoChannels)    {       // \*\*\*we could save time by precalculating this       // schedule end-of-period       nextTics = ServoPeriodTics - ServoPosTics;    }    // read in current value of output compare register OCR3A,    // but within an interrupt so this direct access is safe    OCValue = OCR3A;   // read all 16 bits of OCR3A    //OCValue =  inb(OCR3AL);      // read low byte of OCR3A    //OCValue += inb(OCR3AH)\<\<8;   // read high byte of OCR3A    //TODO REMOVE DEBUG    ServoTimerDebugBuffer[ServoChannel].chan = ServoChannel;    ServoTimerDebugBuffer[ServoChannel].ocval = OCValue;    ServoTimerDebugBuffer[ServoChannel].inc++;    // increment OCR3A value by nextTics    OCValue += nextTics;    //   OCR3A+=nextTics; // but must protect the register so byte wise shift it in    // set future output compare time to this new value    // but within an interrupt so this direct access is safe    OCR3A = OCValue;    //outb(OCR3AH, (OCValue\>\>8));         // write high byte    //outb(OCR3AL, (OCValue & 0x00FF));   // write low byte    // set our new tic position    ServoPosTics += nextTics;    //TODO REMOVE DEBUG    ServoTimerDebugBuffer[ServoChannel].nxt = nextTics;    ServoTimerDebugBuffer[ServoChannel].srvpos = ServoPosTics;    if(ServoPosTics \>= ServoPeriodTics)    {       ServoPosTics = 0;       //The toggle works here       LED\_TOGGLE( YELLOW );       if (xTaskResumeFromISR(ServoDebugTaskHandle) == pdTRUE)       {          //The toggle does not work here          //LED\_TOGGLE( YELLOW );          taskYIELD();       }    } } ---
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [May 26, 2008, 8:27am UTC](https://forums.freertos.org/t/problem-vtasksuspend-and-xtaskresumefromisr/3805/2 "2008-05-26T08:27:07Z")
**[woops\_](https://sourceforge.net/u/woops_/)** wrote on [Monday, May 26, 2008](https://sourceforge.net/p/freertos/discussion/382005/thread/a89fc636/#04b8/aca7): The ResumeFromISR function has the following statement vTaskResumeFromISR() should not be used to synchronise a task with an interrupt if there is a chance that the interrupt could arrive prior to the task being suspended - as this can lead to interrupts being missed. Use of a semaphore as a synchronisation mechanism would avoid this eventuality. could that be the problem? ---
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [May 27, 2008, 7:00am UTC](https://forums.freertos.org/t/problem-vtasksuspend-and-xtaskresumefromisr/3805/3 "2008-05-27T07:00:57Z")
**[wellingj](https://sourceforge.net/u/wellingj/)** wrote on [Tuesday, May 27, 2008](https://sourceforge.net/p/freertos/discussion/382005/thread/a89fc636/#04b8/aca7/5330): That was exactly it… Coincidentally, The example for vTaskResumeFromISR() has a "xSemaphoreCreateBinary()" when it should be a "vSemaphoreCreateBinary()". Had to look at the .h file to figure that one out 😉 Thanks a bunch! ---
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [May 27, 2008, 7:02am UTC](https://forums.freertos.org/t/problem-vtasksuspend-and-xtaskresumefromisr/3805/4 "2008-05-27T07:02:34Z")
**[wellingj](https://sourceforge.net/u/wellingj/)** wrote on [Tuesday, May 27, 2008](https://sourceforge.net/p/freertos/discussion/382005/thread/a89fc636/#04b8/38f0): Correction: The example for xSemaphoreGiveFromISR() had the error… ---
**Author:** ![rtel](https://d3iykfbgfh8zhg.cloudfront.net/user_avatar/forums.freertos.org/rtel/32/31_2.png) [@rtel](https://forums.freertos.org/u/rtel)\ **Post date:** [May 27, 2008, 7:34am UTC](https://forums.freertos.org/t/problem-vtasksuspend-and-xtaskresumefromisr/3805/5 "2008-05-27T07:34:13Z")
**[rtel](https://sourceforge.net/u/rtel/)** wrote on [Tuesday, May 27, 2008](https://sourceforge.net/p/freertos/discussion/382005/thread/a89fc636/#04b8/38f0/4e3f): \>Correction: The example for xSemaphoreGiveFromISR() had the error Fixed - thanks for pointing this out. Regards.