I have question about freertos Fat I’m using iar compiler and stm32f427 scheduling method is preemptive, I‘m using the hal library, I’m using sdcard (sandisk extreme 16g) The graph below relates to the execution time of the SDCARDWRITETask , X-axis is program execution time, Y-axis is the time which the SDCARDWRITETask is complete http://imgur.com/a/MPYMX As shown in graph SDCARDWRITETask is run every 80ms using vTaskDelayUntil, http://imgur.com/P64neiK As shown in graph SDCARDWRITETask is run every 40ms using vTaskDelayUntil As you can see in the graph, This increased to periodically run time (incase 80ms is every 18 second, incase 40ms is every 9 second) **My question this How is this problem occurs when any part of the problem? This is the problem of the code? Or is it a hardware problem ?**

Sorry – I don’t understand your question. Could you try re-phrasing it, although as this is your application, and we don’t know its structure, what is being written, how good the driver is, whether the driver is polling or interrupt driven, or what else the application is doing, it is unlikely we will be able to provide an answer. In the graphs I think I see a periodic write with a fairly fixed write time, with a few longer writes that in between which are not on the same period.