S32K + FreeRTOS: Interrupts are enabled too soon

[jan-bruckner-esr]

In xPortStartScheduler():

openbsw/platforms/s32k1xx/3rdparty/freertos_cm4_sysTick/src/port.c

Lines 389 to 420 in 73fb9cd

	/* Make PendSV and SysTick the lowest priority interrupts. */
	portNVIC_SHPR3_REG |= portNVIC_PENDSV_PRI;
	portNVIC_SHPR3_REG |= portNVIC_SYSTICK_PRI;
	/* Start the timer that generates the tick ISR. Interrupts are disabled
	* here already. */
	vPortSetupTimerInterrupt();
	/* Initialise the critical nesting count ready for the first task. */
	uxCriticalNesting = 0;
	/* Ensure the VFP is enabled - it should be anyway. */
	vPortEnableVFP();
	/* Lazy save always. */
	*( portFPCCR ) |= portASPEN_AND_LSPEN_BITS;
	/* Start the first task. */
	prvPortStartFirstTask();
	/* Should never get here as the tasks will now be executing! Call the task
	* exit error function to prevent compiler warnings about a static function
	* not being called in the case that the application writer overrides this
	* functionality by defining configTASK_RETURN_ADDRESS. Call
	* vTaskSwitchContext() so link time optimisation does not remove the
	* symbol. */
	vTaskSwitchContext();
	prvTaskExitError();
	/* Should not get here! */
	return 0;
	}

vPortSetupTimerInterrupt() is called which calls setupApplicationsIsr():

openbsw/executables/referenceApp/platforms/s32k148evb/main/src/main.cpp

Lines 53 to 74 in 73fb9cd

	void setupApplicationsIsr(void)
	{
	// interrupts
	SYS_SetPriority(CAN0_ORed_0_15_MB_IRQn, 8); // can0 buffer 0 - 15
	SYS_SetPriority(CAN0_ORed_16_31_MB_IRQn, 8); // can0 buffer 16 - 32
	SYS_EnableIRQ(CAN0_ORed_0_15_MB_IRQn);
	SYS_EnableIRQ(CAN0_ORed_16_31_MB_IRQn);
	// Data transfer done, Transmit Buffer Done for Ring/Queue 0, Transmit Frame Done for Ring/Queue
	// 0
	SYS_SetPriority(ENET_TX_Buffer_IRQn, 9);
	// Receive Buffer Done for Ring/Queue 0, Receive Frame Done for Ring/Queue 0
	SYS_SetPriority(ENET_RX_Buffer_IRQn, 9);
	// Payload receive error, Collision retry limit reached, Late collision detected, AXI Bus Error
	// detected, Babbling transmit error, Babbling receive error, Transmit FIFO underrun
	// SYS_SetPriority(ENET_PRE_IRQn, 9);
	SYS_EnableIRQ(ENET_TX_Buffer_IRQn);
	SYS_EnableIRQ(ENET_RX_Buffer_IRQn);
	// SYS_EnableIRQ(ENET_PRE_IRQn);
	ENABLE_INTERRUPTS();
	}

which enables interrupts in the last line.

However, FreeRTOS enables interrupts later in:

openbsw/platforms/s32k1xx/3rdparty/freertos_cm4_sysTick/src/port.c

Lines 270 to 291 in 73fb9cd

	static void prvPortStartFirstTask( void )
	{
	/* Start the first task. This also clears the bit that indicates the FPU is
	* in use in case the FPU was used before the scheduler was started - which
	* would otherwise result in the unnecessary leaving of space in the SVC stack
	* for lazy saving of FPU registers. */
	__asm volatile (
	" ldr r0, =0xE000ED08 \n" /* Use the NVIC offset register to locate the stack. */
	" ldr r0, [r0] \n"
	" ldr r0, [r0] \n"
	" msr msp, r0 \n" /* Set the msp back to the start of the stack. */
	" mov r0, #0 \n" /* Clear the bit that indicates the FPU is in use, see comment above. */
	" msr control, r0 \n"
	" cpsie i \n" /* Globally enable interrupts. */
	" cpsie f \n"
	" dsb \n"
	" isb \n"
	" svc 0 \n" /* System call to start first task. */
	" nop \n"
	" .ltorg \n"
	);
	}

Is there a reason why we enable interrupts ourselves earlier?