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Zynq Port Tick Handler Signature

Posted by razed11 on October 2, 2015

The tick handler is defined as

~~~~ void FreeRTOSTickHandler( void ) ~~~~

It is given a callback reference (&xTimer).

~~~~ xStatus = XScuGicConnect( &xInterruptController, XPARSCUTIMERINTR, (XilExceptionHandler) FreeRTOSTickHandler, ( void * ) &xTimer ); ~~~~

The application IRQ handler calls it as:

~~~~ pxVectorEntry->Handler( pxVectorEntry->CallBackRef ); ~~~~

Should we address this?

Zynq Port Tick Handler Signature

Posted by rtel on October 3, 2015

This was a deliberate decision and considered quite benign as the tick handler is povided by the RTOS, and it does not use the parameter. The only time the compiler will match the prototype of the FreeRTOSTickHandler() function and the prototype of the function passed into XScuGicConnect() is when XScuGicConnect() is itself called - which again is taken care of in the RTOS code.

The line pxVectorEntry->Handler( pxVectorEntry->CallBackRef ); will place a value in register R0, but the function FreeRTOSTickHandler( void ) will never use the value from the register. The alternative is to have FreeRTOSTickHandler( void ) accept a parameter, then use the parameter [as in ( void ) parameter] to avoid compilier warnings, and potentially generate more code if the optimisation level is 0.


Zynq Port Tick Handler Signature

Posted by razed11 on October 5, 2015

Right. R0 is probably stacked so a void (*)(void) method that might make use of that register would not be doing any harm either. I very much doubt that the hard float ABI is different in this regard.

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