portable/RVDS/ARM_CM0/port.c

/*
 * FreeRTOS Kernel V10.3.1
 * Copyright (C) 2020 Amazon.com, Inc. or its affiliates.  All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of
 * this software and associated documentation files (the "Software"), to deal in
 * the Software without restriction, including without limitation the rights to
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so,
 * subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
 * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
 * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
 * IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * http://www.FreeRTOS.org
 * http://aws.amazon.com/freertos
 *
 * 1 tab == 4 spaces!
 */

/*-----------------------------------------------------------
 * Implementation of functions defined in portable.h for the ARM CM0 port.
 *----------------------------------------------------------*/

/* Scheduler includes. */
#include "FreeRTOS.h"
#include "task.h"

/* Constants required to manipulate the NVIC. */
#define portNVIC_SYSTICK_CTRL_REG			( * ( ( volatile uint32_t * ) 0xe000e010 ) )
#define portNVIC_SYSTICK_LOAD_REG			( * ( ( volatile uint32_t * ) 0xe000e014 ) )
#define portNVIC_SYSTICK_CURRENT_VALUE_REG	( * ( ( volatile uint32_t * ) 0xe000e018 ) )
#define portNVIC_INT_CTRL_REG				( * ( ( volatile uint32_t * ) 0xe000ed04 ) )
#define portNVIC_SYSPRI2_REG				( * ( ( volatile uint32_t * ) 0xe000ed20 ) )
#define portNVIC_SYSTICK_CLK_BIT			( 1UL << 2UL )
#define portNVIC_SYSTICK_INT_BIT			( 1UL << 1UL )
#define portNVIC_SYSTICK_ENABLE_BIT			( 1UL << 0UL )
#define portNVIC_SYSTICK_COUNT_FLAG_BIT		( 1UL << 16UL )
#define portNVIC_PENDSVSET_BIT				( 1UL << 28UL )
#define portMIN_INTERRUPT_PRIORITY			( 255UL )
#define portNVIC_PENDSV_PRI					( portMIN_INTERRUPT_PRIORITY << 16UL )
#define portNVIC_SYSTICK_PRI				( portMIN_INTERRUPT_PRIORITY << 24UL )

/* Constants required to set up the initial stack. */
#define portINITIAL_XPSR			( 0x01000000 )

/* The systick is a 24-bit counter. */
#define portMAX_24_BIT_NUMBER		( 0xffffffUL )

/* A fiddle factor to estimate the number of SysTick counts that would have
 occurred while the SysTick counter is stopped during tickless idle
 calculations. */
#ifndef portMISSED_COUNTS_FACTOR
	#define portMISSED_COUNTS_FACTOR	( 45UL )
#endif

/* Constants used with memory barrier intrinsics. */
#define portSY_FULL_READ_WRITE		( 15 )

/* Legacy macro for backward compatibility only.  This macro used to be used to
replace the function that configures the clock used to generate the tick
interrupt (prvSetupTimerInterrupt()), but now the function is declared weak so
the application writer can override it by simply defining a function of the
same name (vApplicationSetupTickInterrupt()). */
#ifndef configOVERRIDE_DEFAULT_TICK_CONFIGURATION
	#define configOVERRIDE_DEFAULT_TICK_CONFIGURATION 0
#endif

/* Each task maintains its own interrupt status in the critical nesting
variable. */
static UBaseType_t uxCriticalNesting = 0xaaaaaaaa;

/* The number of SysTick increments that make up one tick period. */
#if( configUSE_TICKLESS_IDLE == 1 )
	static uint32_t ulTimerCountsForOneTick = 0;
#endif /* configUSE_TICKLESS_IDLE */

/* The maximum number of tick periods that can be suppressed is limited by the
 24 bit resolution of the SysTick timer. */
#if( configUSE_TICKLESS_IDLE == 1 )
	static uint32_t xMaximumPossibleSuppressedTicks = 0;
#endif /* configUSE_TICKLESS_IDLE */

 /* Compensate for the CPU cycles that pass while the SysTick is stopped (low
 power functionality only.
*/
#if( configUSE_TICKLESS_IDLE == 1 )
	static uint32_t ulStoppedTimerCompensation = 0;
#endif /* configUSE_TICKLESS_IDLE */

/*
 * Setup the timer to generate the tick interrupts.  The implementation in this
 * file is weak to allow application writers to change the timer used to
 * generate the tick interrupt.
 */
void vPortSetupTimerInterrupt( void );

/*
 * Exception handlers.
 */
void xPortPendSVHandler( void );
void xPortSysTickHandler( void );
void vPortSVCHandler( void );

/*
 * Start first task is a separate function so it can be tested in isolation.
 */
static void prvPortStartFirstTask( void );

/*
 * Used to catch tasks that attempt to return from their implementing function.
 */
static void prvTaskExitError( void );

/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
StackType_t *pxPortInitialiseStack( StackType_t *pxTopOfStack, TaskFunction_t pxCode, void *pvParameters )
{
	/* Simulate the stack frame as it would be created by a context switch
	interrupt. */
	pxTopOfStack--; /* Offset added to account for the way the MCU uses the stack on entry/exit of interrupts. */
	*pxTopOfStack = portINITIAL_XPSR;	/* xPSR */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) pxCode;	/* PC */
	pxTopOfStack--;
	*pxTopOfStack = ( StackType_t ) prvTaskExitError;	/* LR */
	pxTopOfStack -= 5;	/* R12, R3, R2 and R1. */
	*pxTopOfStack = ( StackType_t ) pvParameters;	/* R0 */
	pxTopOfStack -= 8; /* R11..R4. */

	return pxTopOfStack;
}
/*-----------------------------------------------------------*/

static void prvTaskExitError( void )
{
	/* A function that implements a task must not exit or attempt to return to
	its caller as there is nothing to return to.  If a task wants to exit it
	should instead call vTaskDelete( NULL ).

	Artificially force an assert() to be triggered if configASSERT() is
	defined, then stop here so application writers can catch the error. */
	configASSERT( uxCriticalNesting == ~0UL );
	portDISABLE_INTERRUPTS();
	for( ;; );
}
/*-----------------------------------------------------------*/

void vPortSVCHandler( void )
{
	/* This function is no longer used, but retained for backward
	compatibility. */
}
/*-----------------------------------------------------------*/

__asm void prvPortStartFirstTask( void )
{
	extern pxCurrentTCB;

	PRESERVE8

	/* The MSP stack is not reset as, unlike on M3/4 parts, there is no vector
	table offset register that can be used to locate the initial stack value.
	Not all M0 parts have the application vector table at address 0. */

	ldr	r3, =pxCurrentTCB	/* Obtain location of pxCurrentTCB. */
	ldr r1, [r3]
	ldr r0, [r1]			/* The first item in pxCurrentTCB is the task top of stack. */
	adds r0, #32			/* Discard everything up to r0. */
	msr psp, r0				/* This is now the new top of stack to use in the task. */
	movs r0, #2				/* Switch to the psp stack. */
	msr CONTROL, r0
	isb
	pop {r0-r5}				/* Pop the registers that are saved automatically. */
	mov lr, r5				/* lr is now in r5. */
	pop {r3}				/* The return address is now in r3. */
	pop {r2}				/* Pop and discard the XPSR. */
	cpsie i					/* The first task has its context and interrupts can be enabled. */
	bx r3					/* Finally, jump to the user defined task code. */

	ALIGN
}
/*-----------------------------------------------------------*/

/*
 * See header file for description.
 */
BaseType_t xPortStartScheduler( void )
{
	/* Make PendSV, CallSV and SysTick the same priority as the kernel. */
	portNVIC_SYSPRI2_REG |= portNVIC_PENDSV_PRI;
	portNVIC_SYSPRI2_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;

	/* Start the first task. */
	prvPortStartFirstTask();

	/* Should not get here! */
	return 0;
}
/*-----------------------------------------------------------*/

void vPortEndScheduler( void )
{
	/* Not implemented in ports where there is nothing to return to.
	Artificially force an assert. */
	configASSERT( uxCriticalNesting == 1000UL );
}
/*-----------------------------------------------------------*/

void vPortYield( void )
{
	/* Set a PendSV to request a context switch. */
	portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;

	/* Barriers are normally not required but do ensure the code is completely
	within the specified behaviour for the architecture. */
	__dsb( portSY_FULL_READ_WRITE );
	__isb( portSY_FULL_READ_WRITE );
}
/*-----------------------------------------------------------*/

void vPortEnterCritical( void )
{
    portDISABLE_INTERRUPTS();
    uxCriticalNesting++;
	__dsb( portSY_FULL_READ_WRITE );
	__isb( portSY_FULL_READ_WRITE );
}
/*-----------------------------------------------------------*/

void vPortExitCritical( void )
{
	configASSERT( uxCriticalNesting );
	uxCriticalNesting--;
	if( uxCriticalNesting == 0 )
	{
		portENABLE_INTERRUPTS();
	}
}
/*-----------------------------------------------------------*/

__asm uint32_t ulSetInterruptMaskFromISR( void )
{
	mrs r0, PRIMASK
	cpsid i
	bx lr
}
/*-----------------------------------------------------------*/

__asm void vClearInterruptMaskFromISR( uint32_t ulMask )
{
	msr PRIMASK, r0
	bx lr
}
/*-----------------------------------------------------------*/

__asm void xPortPendSVHandler( void )
{
	extern vTaskSwitchContext
	extern pxCurrentTCB

	PRESERVE8

	mrs r0, psp

	ldr	r3, =pxCurrentTCB 	/* Get the location of the current TCB. */
	ldr	r2, [r3]

	subs r0, #32			/* Make space for the remaining low registers. */
	str r0, [r2]			/* Save the new top of stack. */
	stmia r0!, {r4-r7}		/* Store the low registers that are not saved automatically. */
	mov r4, r8				/* Store the high registers. */
	mov r5, r9
	mov r6, r10
	mov r7, r11
	stmia r0!, {r4-r7}

	push {r3, r14}
	cpsid i
	bl vTaskSwitchContext
	cpsie i
	pop {r2, r3}			/* lr goes in r3. r2 now holds tcb pointer. */

	ldr r1, [r2]
	ldr r0, [r1]			/* The first item in pxCurrentTCB is the task top of stack. */
	adds r0, #16			/* Move to the high registers. */
	ldmia r0!, {r4-r7}		/* Pop the high registers. */
	mov r8, r4
	mov r9, r5
	mov r10, r6
	mov r11, r7

	msr psp, r0				/* Remember the new top of stack for the task. */

	subs r0, #32			/* Go back for the low registers that are not automatically restored. */
	ldmia r0!, {r4-r7}      /* Pop low registers.  */

	bx r3
	ALIGN
}
/*-----------------------------------------------------------*/

void xPortSysTickHandler( void )
{
uint32_t ulPreviousMask;

	ulPreviousMask = portSET_INTERRUPT_MASK_FROM_ISR();
	{
		/* Increment the RTOS tick. */
		if( xTaskIncrementTick() != pdFALSE )
		{
			/* Pend a context switch. */
			portNVIC_INT_CTRL_REG = portNVIC_PENDSVSET_BIT;
		}
	}
	portCLEAR_INTERRUPT_MASK_FROM_ISR( ulPreviousMask );
}
/*-----------------------------------------------------------*/

/*
 * Setup the systick timer to generate the tick interrupts at the required
 * frequency.
 */
#if( configOVERRIDE_DEFAULT_TICK_CONFIGURATION == 0 )

	__weak void vPortSetupTimerInterrupt( void )
	{
		/* Calculate the constants required to configure the tick interrupt. */
		#if( configUSE_TICKLESS_IDLE == 1 )
			ulTimerCountsForOneTick = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ );
			xMaximumPossibleSuppressedTicks = portMAX_24_BIT_NUMBER / ulTimerCountsForOneTick;
			ulStoppedTimerCompensation = portMISSED_COUNTS_FACTOR;
		#endif /* configUSE_TICKLESS_IDLE */

		/* Stop and reset the SysTick. */
		portNVIC_SYSTICK_CTRL_REG = 0UL;
		portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;

		/* Configure SysTick to interrupt at the requested rate. */
		portNVIC_SYSTICK_LOAD_REG = ( configCPU_CLOCK_HZ / configTICK_RATE_HZ ) - 1UL;
		portNVIC_SYSTICK_CTRL_REG = portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT | portNVIC_SYSTICK_ENABLE_BIT;
	}

#endif /* configOVERRIDE_DEFAULT_TICK_CONFIGURATION */
/*-----------------------------------------------------------*/

#if( configUSE_TICKLESS_IDLE == 1 )

__weak void vPortSuppressTicksAndSleep( TickType_t xExpectedIdleTime )
{
uint32_t ulReloadValue, ulCompleteTickPeriods, ulCompletedSysTickDecrements;
TickType_t xModifiableIdleTime;

	/* Make sure the SysTick reload value does not overflow the counter. */
	if( xExpectedIdleTime > xMaximumPossibleSuppressedTicks )
	{
		xExpectedIdleTime = xMaximumPossibleSuppressedTicks;
	}

	/* Stop the SysTick momentarily. The time the SysTick is stopped for
	is accounted for as best it can be, but using the tickless mode will
	inevitably result in some tiny drift of the time maintained by the
	kernel with respect to calendar time. */
	portNVIC_SYSTICK_CTRL_REG &= ~portNVIC_SYSTICK_ENABLE_BIT;

	/* Calculate the reload value required to wait xExpectedIdleTime
	tick periods.  -1 is used because this code will execute part way
	through one of the tick periods. */
	ulReloadValue = portNVIC_SYSTICK_CURRENT_VALUE_REG + ( ulTimerCountsForOneTick * ( xExpectedIdleTime - 1UL ) );
	if( ulReloadValue > ulStoppedTimerCompensation )
	{
		ulReloadValue -= ulStoppedTimerCompensation;
	}

	/* Enter a critical section but don't use the taskENTER_CRITICAL()
	method as that will mask interrupts that should exit sleep mode. */
	__disable_irq();
	__dsb( portSY_FULL_READ_WRITE );
	__isb( portSY_FULL_READ_WRITE );

	/* If a context switch is pending or a task is waiting for the scheduler
	to be unsuspended then abandon the low power entry. */
	if( eTaskConfirmSleepModeStatus() == eAbortSleep )
	{
		/* Restart from whatever is left in the count register to complete
		this tick period. */
		portNVIC_SYSTICK_LOAD_REG = portNVIC_SYSTICK_CURRENT_VALUE_REG;

		/* Restart SysTick. */
		portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;

		/* Reset the reload register to the value required for normal tick
		periods. */
		portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;

		/* Re-enable interrupts - see comments above __disable_irq() call
		above. */
		__enable_irq();
	}
	else
	{
		/* Set the new reload value. */
		portNVIC_SYSTICK_LOAD_REG = ulReloadValue;

		/* Clear the SysTick count flag and set the count value back to
		zero. */
		portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;

		/* Restart SysTick. */
		portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;

		/* Sleep until something happens. configPRE_SLEEP_PROCESSING() can
		set its parameter to 0 to indicate that its implementation contains
		its own wait for interrupt or wait for event instruction, and so wfi
		should not be executed again. However, the original expected idle
		time variable must remain unmodified, so a copy is taken. */
		xModifiableIdleTime = xExpectedIdleTime;
		configPRE_SLEEP_PROCESSING( xModifiableIdleTime );
		if( xModifiableIdleTime > 0 )
		{
			__dsb( portSY_FULL_READ_WRITE );
			__wfi();
			__isb( portSY_FULL_READ_WRITE );
		}
		configPOST_SLEEP_PROCESSING( xExpectedIdleTime );

		/* Re-enable interrupts to allow the interrupt that brought the MCU
		out of sleep mode to execute immediately. see comments above
		__disable_interrupt() call above. */
		__enable_irq();
		__dsb( portSY_FULL_READ_WRITE );
		__isb( portSY_FULL_READ_WRITE );

		/* Disable interrupts again because the clock is about to be stopped
		and interrupts that execute while the clock is stopped will increase
		any slippage between the time maintained by the RTOS and calendar
		time. */
		__disable_irq();
		__dsb( portSY_FULL_READ_WRITE );
		__isb( portSY_FULL_READ_WRITE );

		/* Disable the SysTick clock without reading the
		portNVIC_SYSTICK_CTRL_REG register to ensure the
		portNVIC_SYSTICK_COUNT_FLAG_BIT is not cleared if it is set.  Again,
		the time the SysTick is stopped for is accounted for as best it can
		be, but using the tickless mode will inevitably result in some tiny
		drift of the time maintained by the kernel with respect to calendar
		time*/
		portNVIC_SYSTICK_CTRL_REG = ( portNVIC_SYSTICK_CLK_BIT | portNVIC_SYSTICK_INT_BIT );

		/* Determine if the SysTick clock has already counted to zero and
		been set back to the current reload value (the reload back being
		correct for the entire expected idle time) or if the SysTick is yet
		to count to zero (in which case an interrupt other than the SysTick
		must have brought the system out of sleep mode). */
		if( ( portNVIC_SYSTICK_CTRL_REG & portNVIC_SYSTICK_COUNT_FLAG_BIT ) != 0 )
		{
			uint32_t ulCalculatedLoadValue;

			/* The tick interrupt is already pending, and the SysTick count
			reloaded with ulReloadValue.  Reset the
			portNVIC_SYSTICK_LOAD with whatever remains of this tick
			period. */
			ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL ) - ( ulReloadValue - portNVIC_SYSTICK_CURRENT_VALUE_REG );

			/* Don't allow a tiny value, or values that have somehow
			underflowed because the post sleep hook did something
			that took too long. */
			if( ( ulCalculatedLoadValue < ulStoppedTimerCompensation ) || ( ulCalculatedLoadValue > ulTimerCountsForOneTick ) )
			{
				ulCalculatedLoadValue = ( ulTimerCountsForOneTick - 1UL );
			}

			portNVIC_SYSTICK_LOAD_REG = ulCalculatedLoadValue;

			/* As the pending tick will be processed as soon as this
			function exits, the tick value maintained by the tick is stepped
			forward by one less than the time spent waiting. */
			ulCompleteTickPeriods = xExpectedIdleTime - 1UL;
		}
		else
		{
			/* Something other than the tick interrupt ended the sleep.
			Work out how long the sleep lasted rounded to complete tick
			periods (not the ulReload value which accounted for part
			ticks). */
			ulCompletedSysTickDecrements = ( xExpectedIdleTime * ulTimerCountsForOneTick ) - portNVIC_SYSTICK_CURRENT_VALUE_REG;

			/* How many complete tick periods passed while the processor
			was waiting? */
			ulCompleteTickPeriods = ulCompletedSysTickDecrements / ulTimerCountsForOneTick;

			/* The reload value is set to whatever fraction of a single tick
			period remains. */
			portNVIC_SYSTICK_LOAD_REG = ( ( ulCompleteTickPeriods + 1UL ) * ulTimerCountsForOneTick ) - ulCompletedSysTickDecrements;
		}

		/* Restart SysTick so it runs from portNVIC_SYSTICK_LOAD
		again, then set portNVIC_SYSTICK_LOAD back to its standard
		value. */
		portNVIC_SYSTICK_CURRENT_VALUE_REG = 0UL;
		portNVIC_SYSTICK_CTRL_REG |= portNVIC_SYSTICK_ENABLE_BIT;
		vTaskStepTick( ulCompleteTickPeriods );
		portNVIC_SYSTICK_LOAD_REG = ulTimerCountsForOneTick - 1UL;

		/* Exit with interrpts enabled. */
		__enable_irq();
	}
}

#endif /* #if configUSE_TICKLESS_IDLE */

/*-----------------------------------------------------------*/