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using isr before vTaskStartScheduler() starte

Posted by Bernd Schuster on November 24, 2009
Hi,

is it recommended to start an usart_isr before the vTaskStartScheduler() will be started? Are there any kind of drawbacks? Which configuration would you suggest (using a semaphore or global variable within the isr)?

best regards
Bernd

RE: using isr before vTaskStartScheduler() starte

Posted by Dave on November 24, 2009
Normally interrupts will be disabled before the scheduler is started. If you do use interrupts before the scheduler is started then you must ensure that no interrupt service routines try and perform a context switch, as to do so before the scheduler was initialized would cause a crash.

RE: using isr before vTaskStartScheduler() starte

Posted by Bernd Schuster on November 24, 2009
Do you know a recommended way to enable the interrupts after starting the scheduler? If the usage of a global variable is perfect, where do I have to set this variable (to enable the interrupts)?

Or is it possible using the variable xSchedulerRunning = pdTRUE;
-> if true is correct, interrupts are enabled.

RE: using isr before vTaskStartScheduler() starte

Posted by Dave on November 24, 2009
Interrupts will be enabled automatically when the first task starts running (assuming the FreeRTOS code is unchanged) so you don't need to do anything from the application code. If you want the interrupt handler to only execute when the scheduler is running then testing xSchedulerRunning is a good method, but be careful as some ports require the task context to be saved before any C code executes, so before you can test the xSchedulerRunning value.


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