# xSemaphoreGiveFromISR() problems **URL:** \ **Category:** Kernel\ **Created:** [January 7, 2013, 10:17pm UTC](https://forums.freertos.org/t/xsemaphoregivefromisr-problems/1289 "2013-01-07T22:17:49Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![system](https://d2v6vdsk2p900z.cloudfront.net/original/1X/7fc8fdb729c645aab5b20282bbe34e57cb407be6.jpeg) [@system](https://forums.freertos.org/u/system)\ **Post date:** [January 7, 2013, 10:17pm UTC](https://forums.freertos.org/t/xsemaphoregivefromisr-problems/1289/1 "2013-01-07T22:17:49Z")
**[rnodes](https://sourceforge.net/u/rnodes/)** wrote on [Monday, January 07, 2013](https://sourceforge.net/p/freertos/discussion/382005/thread/37c3e996/#e0fd): I have two ISRs using  xSemaphoreGiveFromISR() fuction call and one over a long period of time never gets called and the other has missed its call here and there. I suspect that there is a priority issue with this function that causes it to fail. I am using version 7 of freeRTOS. Has anyone had this issue where the ist just gets blocked? ---
**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:** [January 8, 2013, 9:17am UTC](https://forums.freertos.org/t/xsemaphoregivefromisr-problems/1289/2 "2013-01-08T09:17:14Z")
**[rtel](https://sourceforge.net/u/rtel/)** wrote on [Tuesday, January 08, 2013](https://sourceforge.net/p/freertos/discussion/382005/thread/37c3e996/#e21b): Which port are you using? What type of semaphore is it (binary/counting/etc.)? > one over a long period of time never gets called What doesn’t get called?  The ISR?  What is triggering the ISR (UART, DMA, SPI, external, etc.)?  Are you sure the ISR is configured and cleared correctly?  > the other has missed its call here and there What has missed its call?  The interrupt?  Do you have critical sections that are too long for the frequency at which the interrupts are arriving? Regards.