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/*
* FreeRTOS Kernel <DEVELOPMENT BRANCH>
* Copyright (C) 2021 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.
*
* https://www.FreeRTOS.org
* https://github.com/FreeRTOS
*
*/
/*-----------------------------------------------------------
* 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_SHPR3_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. */
/* *INDENT-OFF* */
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
/* *INDENT-ON* */
}
/*-----------------------------------------------------------*/
/*
* See header file for description.
*/
BaseType_t xPortStartScheduler( void )
{
/* Make PendSV, CallSV and SysTick the same priority as the kernel. */
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;
/* 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 )
{
/* *INDENT-OFF* */
mrs r0, PRIMASK
cpsid i
bx lr
/* *INDENT-ON* */
}
/*-----------------------------------------------------------*/
__asm void vClearInterruptMaskFromISR( uint32_t ulMask )
{
/* *INDENT-OFF* */
msr PRIMASK, r0
bx lr
/* *INDENT-ON* */
}
/*-----------------------------------------------------------*/
__asm void xPortPendSVHandler( void )
{
extern vTaskSwitchContext
extern pxCurrentTCB
/* *INDENT-OFF* */
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
/* *INDENT-ON* */
}
/*-----------------------------------------------------------*/
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 */
/*-----------------------------------------------------------*/