CORE - Core Interrupt

Description

Core interrupt handling API.


Introduction

CORE interrupt API provides a simple and safe means to disable and enable interrupts to protect sections of code.

This is often referred to as "critical sections". This module provides support for three types of critical sections, each with different interrupt blocking capabilities.

  • CRITICAL section: Inside a critical section, all interrupts are disabled (except for fault handlers). The PRIMASK register is always used for interrupt disable/enable.
  • ATOMIC section: This type of section is configurable and the default method is to use PRIMASK. With BASEPRI configuration, interrupts with priority equal to or lower than a given configurable level are disabled. The interrupt disable priority level is defined at compile time. The BASEPRI register is not available for all architectures.
  • NVIC mask section: Disable NVIC (external interrupts) on an individual manner.

em_core also has an API for manipulating RAM-based interrupt vector tables.


Compile-time Configuration

The following #defines are used to configure em_core:

// The interrupt priority level used inside ATOMIC sections.
#define CORE_ATOMIC_BASE_PRIORITY_LEVEL 3
// A method used for interrupt disable/enable within ATOMIC sections.
#define CORE_ATOMIC_METHOD CORE_ATOMIC_METHOD_PRIMASK

If the default values do not support your needs, they can be overridden by supplying -D compiler flags on the compiler command line or by collecting all macro redefinitions in a file named emlib_config.h and then supplying -DEMLIB_USER_CONFIG on a compiler command line.

Note
The default emlib configuration for ATOMIC section interrupt disable method is using PRIMASK, i.e., ATOMIC sections are implemented as CRITICAL sections.
Due to architectural limitations Cortex-M0+ devices do not support ATOMIC type critical sections using the BASEPRI register. On M0+ devices ATOMIC section helper macros are available but they are implemented as CRITICAL sections using PRIMASK register.


Macro API

The primary em_core API is the macro API. Macro API will map to correct CORE functions according to the selected CORE_ATOMIC_METHOD and similar configurations (the full CORE API is of course also available). The most useful macros are as follows:

CORE_DECLARE_IRQ_STATE
CORE_ENTER_ATOMIC()
CORE_EXIT_ATOMIC()
Used together to implement an ATOMIC section.

{
CORE_DECLARE_IRQ_STATE; // Storage for saving IRQ state prior to
// atomic section entry.
CORE_ENTER_ATOMIC(); // Enter atomic section.
...
... your code goes here ...
...
CORE_EXIT_ATOMIC(); // Exit atomic section, IRQ state is restored.
}


CORE_ATOMIC_SECTION(yourcode)
A concatenation of all three macros above.

{
...
... your code goes here ...
...
)
}


CORE_DECLARE_IRQ_STATE
CORE_ENTER_CRITICAL()
CORE_EXIT_CRITICAL()
CORE_CRITICAL_SECTION(yourcode)
These macros implement CRITICAL sections in a similar fashion as described above for ATOMIC sections.


CORE_DECLARE_NVIC_STATE
CORE_ENTER_NVIC()
CORE_EXIT_NVIC()
CORE_NVIC_SECTION(yourcode)
These macros implement NVIC mask sections in a similar fashion as described above for ATOMIC sections. See Examples for an example.

Refer to Macros or Macro Definition Documentation below for a full list of macros.


API reimplementation

Most of the functions in the API are implemented as weak functions. This means that it is easy to reimplement when special needs arise. Shown below is a reimplementation of CRITICAL sections suitable if FreeRTOS OS is used:

{
vPortEnterCritical();
return 0;
}
{
(void)irqState;
vPortExitCritical();
}

Also note that CORE_Enter/ExitCritical() are not implemented as inline functions. As a result, reimplementations will be possible even when original implementations are inside a linked library.

Some RTOSes must be notified on interrupt handler entry and exit. Macros CORE_INTERRUPT_ENTRY() and CORE_INTERRUPT_EXIT() are suitable placeholders for inserting such code. Insert these macros in all your interrupt handlers and then override the default macro implementations. This is an example if uC/OS is used:

// In emlib_config.h:
#define CORE_INTERRUPT_ENTRY() OSIntEnter()
#define CORE_INTERRUPT_EXIT() OSIntExit()


Interrupt vector tables

When using RAM based interrupt vector tables it is the user's responsibility to allocate the table space correctly. The tables must be aligned as specified in the CPU reference manual.

CORE_InitNvicVectorTable()
Initialize a RAM based vector table by copying table entries from a source vector table to a target table. VTOR is set to the address of the target vector table.


CORE_GetNvicRamTableHandler()
CORE_SetNvicRamTableHandler()
Use these functions to get or set the interrupt handler for a specific IRQn. They both use the interrupt vector table defined by the current VTOR register value.


Maximum Interrupt Disabled Time

The maximum time spent (in cycles) in critical and atomic sections can be measured for performance and interrupt latency analysis. To activate this feature, the Cycle Counter driver must be included in the project. To enable the timings, use the SL_EMLIB_CORE_ENABLE_INTERRUPT_DISABLED_TIMING configuration option. When enabled, the functions
CORE_get_max_time_critical_section()
CORE_get_max_time_atomic_section()
can be used to get the max timings since startup.


Examples

Implement an NVIC critical section:

{
CORE_DECLARE_NVIC_ZEROMASK(mask); // A zero initialized NVIC disable mask
// Set mask bits for IRQs to block in the NVIC critical section.
// In many cases, you can create the disable mask once upon application
// startup and use the mask globally throughout the application lifetime.
CORE_NvicMaskSetIRQ(LEUART0_IRQn, &mask);
CORE_NvicMaskSetIRQ(VCMP_IRQn, &mask);
// Enter NVIC critical section with the disable mask
...
... your code goes here ...
...
)
}


Porting from em_int

Existing code using INT_Enable() and INT_Disable() must be ported to the em_core API. While em_int used, a global counter to store the interrupt state, em_core uses a local variable. Any usage of INT_Disable(), therefore, needs to be replaced with a declaration of the interrupt state variable before entering the critical section.

Since the state variable is in local scope, the critical section exit needs to occur within the scope of the variable. If multiple nested critical sections are used, each needs to have its own state variable in its own scope.

In many cases, completely disabling all interrupts using CRITICAL sections might be more heavy-handed than needed. When porting, consider whether other types of sections, such as ATOMIC or NVIC mask, can be used to only disable a subset of the interrupts.

Replacing em_int calls with em_core function calls:

void func(void)
{
// INT_Disable();
.
.
.
// INT_Enable();
}

Data Structures

struct  CORE_nvicMask_t
 Storage for NVIC interrupt masks.
 

Functions

void CORE_CriticalDisableIrq (void)
 Disable interrupts.
 
void CORE_CriticalEnableIrq (void)
 Enable interrupts.
 
CORE_irqState_t CORE_EnterCritical (void)
 Enter a CRITICAL section.
 
void CORE_ExitCritical (CORE_irqState_t irqState)
 Exit a CRITICAL section.
 
void CORE_YieldCritical (void)
 Brief interrupt enable/disable sequence to allow handling of pending interrupts.
 
void CORE_AtomicDisableIrq (void)
 Disable interrupts.
 
void CORE_AtomicEnableIrq (void)
 Enable interrupts.
 
CORE_irqState_t CORE_EnterAtomic (void)
 Enter an ATOMIC section.
 
void CORE_ExitAtomic (CORE_irqState_t irqState)
 Exit an ATOMIC section.
 
void CORE_YieldAtomic (void)
 Brief interrupt enable/disable sequence to allow handling of pending interrupts.
 
void CORE_EnterNvicMask (CORE_nvicMask_t *nvicState, const CORE_nvicMask_t *disable)
 Enter a NVIC mask section.
 
void CORE_NvicDisableMask (const CORE_nvicMask_t *disable)
 Disable NVIC interrupts.
 
void CORE_NvicEnableMask (const CORE_nvicMask_t *enable)
 Set current NVIC interrupt enable mask.
 
void CORE_YieldNvicMask (const CORE_nvicMask_t *enable)
 Brief NVIC interrupt enable/disable sequence to allow handling of pending interrupts.
 
void CORE_NvicMaskSetIRQ (IRQn_Type irqN, CORE_nvicMask_t *mask)
 Utility function to set an IRQn bit in a NVIC enable/disable mask.
 
void CORE_NvicMaskClearIRQ (IRQn_Type irqN, CORE_nvicMask_t *mask)
 Utility function to clear an IRQn bit in a NVIC enable/disable mask.
 
bool CORE_InIrqContext (void)
 Check whether the current CPU operation mode is handler mode.
 
bool CORE_IrqIsBlocked (IRQn_Type irqN)
 Check if a specific interrupt is disabled or blocked.
 
bool CORE_IrqIsDisabled (void)
 Check if interrupts are disabled.
 
void CORE_GetNvicEnabledMask (CORE_nvicMask_t *mask)
 Get the current NVIC enable mask state.
 
bool CORE_GetNvicMaskDisableState (const CORE_nvicMask_t *mask)
 Get NVIC disable state for a given mask.
 
bool CORE_NvicIRQDisabled (IRQn_Type irqN)
 Check if an NVIC interrupt is disabled.
 
void * CORE_GetNvicRamTableHandler (IRQn_Type irqN)
 Utility function to get the handler for a specific interrupt.
 
void CORE_SetNvicRamTableHandler (IRQn_Type irqN, void *handler)
 Utility function to set the handler for a specific interrupt.
 
void CORE_InitNvicVectorTable (uint32_t *sourceTable, uint32_t sourceSize, uint32_t *targetTable, uint32_t targetSize, void *defaultHandler, bool overwriteActive)
 Initialize an interrupt vector table by copying table entries from a source to a target table.
 
uint32_t CORE_get_max_time_critical_section (void)
 Returns the max time spent in critical section.
 
uint32_t CORE_get_max_time_atomic_section (void)
 Returns the max time spent in atomic section.
 

Macros

#define CORE_DECLARE_IRQ_STATE
 Allocate storage for PRIMASK or BASEPRI value for use by CORE_ENTER/EXIT_ATOMIC() and CORE_ENTER/EXIT_CRITICAL() macros.
 
#define CORE_CRITICAL_IRQ_DISABLE()
 CRITICAL style interrupt disable.
 
#define CORE_CRITICAL_IRQ_ENABLE()
 CRITICAL style interrupt enable.
 
#define CORE_CRITICAL_SECTION(yourcode)
 Convenience macro for implementing a CRITICAL section.
 
#define CORE_ENTER_CRITICAL()
 Enter CRITICAL section.
 
#define CORE_EXIT_CRITICAL()
 Exit CRITICAL section.
 
#define CORE_YIELD_CRITICAL()
 CRITICAL style yield.
 
#define CORE_ATOMIC_IRQ_DISABLE()
 ATOMIC style interrupt disable.
 
#define CORE_ATOMIC_IRQ_ENABLE()
 ATOMIC style interrupt enable.
 
#define CORE_ATOMIC_SECTION(yourcode)
 Convenience macro for implementing an ATOMIC section.
 
#define CORE_ENTER_ATOMIC()
 Enter ATOMIC section.
 
#define CORE_EXIT_ATOMIC()
 Exit ATOMIC section.
 
#define CORE_YIELD_ATOMIC()
 ATOMIC style yield.
 
#define CORE_INTERRUPT_ENTRY()
 Placeholder for optional interrupt handler entry code.
 
#define CORE_INTERRUPT_EXIT()
 Placeholder for optional interrupt handler exit code.
 
#define CORE_ATOMIC_METHOD_PRIMASK   0
 Use PRIMASK register to disable interrupts in ATOMIC sections.
 
#define CORE_ATOMIC_METHOD_BASEPRI   1
 Use BASEPRI register to disable interrupts in ATOMIC sections.
 
#define CORE_NVIC_REG_WORDS   ((EXT_IRQ_COUNT + 31) / 32)
 Number of words in a NVIC mask set.
 
#define CORE_DEFAULT_VECTOR_TABLE_ENTRIES   (EXT_IRQ_COUNT + 16)
 Number of entries in a default interrupt vector table.
 
#define CORE_INTERRUPT_HIGHEST_PRIORITY   0
 Highest priority for core interrupt.
 
#define CORE_INTERRUPT_DEFAULT_PRIORITY   5
 Default priority for core interrupt.
 
#define CORE_INTERRUPT_LOWEST_PRIORITY   7
 Lowest priority for core interrupt.
 
#define CORE_ATOMIC_METHOD_DEFAULT   CORE_ATOMIC_METHOD_BASEPRI
 Default method to disable interrupts in ATOMIC sections.
 
#define CORE_ATOMIC_BASE_PRIORITY_LEVEL   3
 The interrupt priority level disabled within ATOMIC regions.
 
#define CORE_ATOMIC_METHOD   CORE_ATOMIC_METHOD_PRIMASK
 Specify which method to use when implementing ATOMIC sections.
 
#define CORE_DECLARE_IRQ_STATE   CORE_irqState_t irqState
 Allocate storage for PRIMASK or BASEPRI value for use by CORE_ENTER/EXIT_ATOMIC() and CORE_ENTER/EXIT_CRITICAL() macros.
 
#define CORE_CRITICAL_IRQ_DISABLE()   CORE_CriticalDisableIrq()
 CRITICAL style interrupt disable.
 
#define CORE_CRITICAL_IRQ_ENABLE()   CORE_CriticalEnableIrq()
 CRITICAL style interrupt enable.
 
#define CORE_CRITICAL_SECTION(yourcode)
 Convenience macro for implementing a CRITICAL section.
 
#define CORE_ENTER_CRITICAL()   irqState = CORE_EnterCritical()
 Enter CRITICAL section.
 
#define CORE_EXIT_CRITICAL()   CORE_ExitCritical(irqState)
 Exit CRITICAL section.
 
#define CORE_YIELD_CRITICAL()   CORE_YieldCritical()
 CRITICAL style yield.
 
#define CORE_ATOMIC_IRQ_DISABLE()   CORE_AtomicDisableIrq()
 ATOMIC style interrupt disable.
 
#define CORE_ATOMIC_IRQ_ENABLE()   CORE_AtomicEnableIrq()
 ATOMIC style interrupt enable.
 
#define CORE_ATOMIC_SECTION(yourcode)
 Convenience macro for implementing an ATOMIC section.
 
#define CORE_ENTER_ATOMIC()   irqState = CORE_EnterAtomic()
 Enter ATOMIC section.
 
#define CORE_EXIT_ATOMIC()   CORE_ExitAtomic(irqState)
 Exit ATOMIC section.
 
#define CORE_YIELD_ATOMIC()   CORE_YieldAtomic()
 ATOMIC style yield.
 
#define CORE_DECLARE_NVIC_STATE   CORE_nvicMask_t nvicState
 Allocate storage for NVIC interrupt masks for use by CORE_ENTER/EXIT_NVIC() macros.
 
#define CORE_DECLARE_NVIC_MASK(x)   CORE_nvicMask_t x
 Allocate storage for NVIC interrupt masks.
 
#define CORE_DECLARE_NVIC_ZEROMASK(x)   CORE_nvicMask_t x = { { 0 } }
 Allocate storage for and zero initialize NVIC interrupt mask.
 
#define CORE_NVIC_DISABLE(mask)   CORE_NvicDisableMask(mask)
 NVIC mask style interrupt disable.
 
#define CORE_NVIC_ENABLE(mask)   CORE_NvicEnableMask(mask)
 NVIC mask style interrupt enable.
 
#define CORE_NVIC_SECTION(mask, yourcode)
 Convenience macro for implementing a NVIC mask section.
 
#define CORE_ENTER_NVIC(disable)   CORE_EnterNvicMask(&nvicState, disable)
 Enter NVIC mask section.
 
#define CORE_EXIT_NVIC()   CORE_NvicEnableMask(&nvicState)
 Exit NVIC mask section.
 
#define CORE_YIELD_NVIC(enable)   CORE_YieldNvicMask(enable)
 NVIC maks style yield.
 
#define CORE_IRQ_DISABLED()   CORE_IrqIsDisabled()
 Check if IRQ is disabled.
 
#define CORE_IN_IRQ_CONTEXT()   CORE_InIrqContext()
 Check if inside an IRQ handler.
 
#define START_COUNTER(handle)
 Start counter.
 
#define STOP_COUNTER(handle)
 Stop counter.
 

Typedefs

typedef uint32_t CORE_irqState_t
 Storage for PRIMASK or BASEPRI value.
 

Function Documentation

◆ CORE_CriticalDisableIrq()

void CORE_CriticalDisableIrq ( void  )

Disable interrupts.

Disable all interrupts by setting PRIMASK. (Fault exception handlers will still be enabled).

◆ CORE_CriticalEnableIrq()

void CORE_CriticalEnableIrq ( void  )

Enable interrupts.

Enable interrupts by clearing PRIMASK.

◆ CORE_EnterCritical()

CORE_irqState_t CORE_EnterCritical ( void  )

Enter a CRITICAL section.

When a CRITICAL section is entered, all interrupts (except fault handlers) are disabled.

Returns
The value of PRIMASK register prior to the CRITICAL section entry.

◆ CORE_ExitCritical()

void CORE_ExitCritical ( CORE_irqState_t  irqState)

Exit a CRITICAL section.

Parameters
[in]irqStateThe interrupt priority blocking level to restore to PRIMASK when exiting the CRITICAL section. This value is usually the one returned by a prior call to CORE_EnterCritical().

◆ CORE_YieldCritical()

void CORE_YieldCritical ( void  )

Brief interrupt enable/disable sequence to allow handling of pending interrupts.

Note
Usually used within a CRITICAL section.

◆ CORE_AtomicDisableIrq()

void CORE_AtomicDisableIrq