Zynq Port Tick Handler Signature

razed11 wrote on Friday, October 02, 2015:

The tick handler is defined as

void FreeRTOS_Tick_Handler( void )

It is given a callback reference (&xTimer).

	xStatus = XScuGic_Connect( &xInterruptController, XPAR_SCUTIMER_INTR, (Xil_ExceptionHandler) FreeRTOS_Tick_Handler, ( void * ) &xTimer );

The application IRQ handler calls it as:

		pxVectorEntry->Handler( pxVectorEntry->CallBackRef );

Should we address this?

rtel wrote on Saturday, October 03, 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 FreeRTOS_Tick_Handler() function and the prototype of the function passed into XScuGic_Connect() is when XScuGic_Connect() 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 FreeRTOS_Tick_Handler( void ) will never use the value from the register. The alternative is to have FreeRTOS_Tick_Handler( 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.


razed11 wrote on Monday, October 05, 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.