Generic functions to access the Interrupt Controller. More...

Content
	IRQ Mode Bit-Masks
	Configure interrupt line mode.

	IRQ Priority Bit-Masks
	Definitions used by interrupt priority functions.

Functions
int32_t	IRQ_Initialize (void)
	Initialize interrupt controller. More...

int32_t	IRQ_SetHandler (IRQn_ID_t irqn, IRQHandler_t handler)
	Register interrupt handler. More...

IRQHandler_t	IRQ_GetHandler (IRQn_ID_t irqn)
	Get the registered interrupt handler. More...

int32_t	IRQ_Enable (IRQn_ID_t irqn)
	Enable interrupt. More...

int32_t	IRQ_Disable (IRQn_ID_t irqn)
	Disable interrupt. More...

uint32_t	IRQ_GetEnableState (IRQn_ID_t irqn)
	Get interrupt enable state. More...

int32_t	IRQ_SetMode (IRQn_ID_t irqn, uint32_t mode)
	Configure interrupt request mode. More...

uint32_t	IRQ_GetMode (IRQn_ID_t irqn)
	Get interrupt mode configuration. More...

IRQn_ID_t	IRQ_GetActiveIRQ (void)
	Get ID number of current interrupt request (IRQ). More...

IRQn_ID_t	IRQ_GetActiveFIQ (void)
	Get ID number of current fast interrupt request (FIQ). More...

int32_t	IRQ_EndOfInterrupt (IRQn_ID_t irqn)
	Signal end of interrupt processing. More...

int32_t	IRQ_SetPending (IRQn_ID_t irqn)
	Set interrupt pending flag. More...

uint32_t	IRQ_GetPending (IRQn_ID_t irqn)
	Get interrupt pending flag. More...

int32_t	IRQ_ClearPending (IRQn_ID_t irqn)
	Clear interrupt pending flag. More...

int32_t	IRQ_SetPriority (IRQn_ID_t irqn, uint32_t priority)
	Set interrupt priority value. More...

uint32_t	IRQ_GetPriority (IRQn_ID_t irqn)
	Get interrupt priority. More...

int32_t	IRQ_SetPriorityMask (uint32_t priority)
	Set priority masking threshold. More...

uint32_t	IRQ_GetPriorityMask (void)
	Get priority masking threshold. More...

int32_t	IRQ_SetPriorityGroupBits (uint32_t bits)
	Set priority grouping field split point. More...

uint32_t	IRQ_GetPriorityGroupBits (void)
	Get priority grouping field split point. More...

Description

This section describes the device agnostic interrupt API viable for a wide range of specific interrupt controllers. The IRQ Controller API allows interrupt dependend applications to be easily portable across a wide range of controllers.

Note: The default implementation for Arm GIC (Generic Interrupt Controller) can be found in irq_ctrl_gic.c. It uses weak functions thus it can easily be overwritten by an alternative user implementation if needed.

The Armv7-A architecture defines a common set of first level exceptions, see table below.

Exception	CMSIS Handler	Offset	Description
Reset	Reset_Handler	0x0000	First instruction executed after reset.
Undefined Instruction (Undef)	Undef_Handler	0x0004	Signals usage of an illegal instructions.
Supervisor Call (SVC)	SVC_Handler	0x0008	Issued by software using SVC instruction.
Prefetch Abort (PAbt)	PAbt_Handler	0x000C	Signals a memory abort on istruction fetch.
Data Abort (DAbt)	DAbt_Handler	0x0010	Signals a memory abort on data read or write.
Hyp Trap	(NOP)	0x0014	Hypervisor instruction trap, only available with Virtualization Extensions.
IRQ interrupt	IRQ_Handler	0x0018	Interrupt Request (typically from Interrupt Controller)
FIQ interrupt	FIQ_Handler	0x001C	Fast Interrupt Request (typically from Interrupt Controller)

By default those handlers are defined as weak empty functions by the device specific startup code. Software and peripheral interrupts are all handled by one of the both central interrupt handlers (IRQ and FIQ). These needs to be implemented application specific. If an RTOS is used the interrupt handlers are typically provided by the RTOS, e.g. when using RTX5.

The interrupts available depends on the actual device in use. According to CMSIS specification the interrupts are defined as IRQn_Type in Device Header File <device.h>. Using the generic IRQ API one can easily enable and disable interrupts, set up priorities, modes and preemption rules, and register interrupt callbacks.

Example:

void SGI0_Handler() {
  /* 
   * Handle Interrupt 
   */
  
  IRQ_ClearPending((IRQn_ID_t)SGI0_IRQn);
}
 
void main() {
  /* Initialize the Interrupt Controller */
  IRQ_Initialize();
  
  /* Register the user defined handler function */
  IRQ_SetHandler((IRQn_ID_t)SGI0_IRQn, SGI0_Handler);  
  
  /* Set the priority considering the priority grouping */
  const uint32_t subprio = IRQ_GetPriorityGroupBits();
  IRQ_SetPriority((IRQn_ID_t)SGI0_IRQn, 1u << subprio);
  
  /* Set interrupt mode to falling edge */
  IRQ_SetMode((IRQn_ID_t)SGI0_IRQn, IRQ_MODE_TYPE_IRQ | IRQ_MODE_CPU_0 | IRQ_MODE_TRIG_EDGE | IRQ_MODE_TRIG_EDGE_FALLING);
  
  IRQ_Enable((IRQn_ID_t)SGI0_IRQn);
  
  /* Trigger interrupt */
  IRQ_SetPending((IRQn_ID_t)SGI0_IRQn);
  
  IRQ_Disable((IRQn_ID_t)SGI0_IRQn);
}

Function Documentation

int32_t IRQ_ClearPending ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: 0 on success, -1 on error.

This function clears the pending status of the interrupt identified by the irqn parameter.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_ClearPending (IRQn_ID_t irqn) {
  int32_t status;
 
  if ((irqn >= 16) && (irqn < IRQ_GIC_LINE_COUNT)) {
    GIC_ClearPendingIRQ ((IRQn_Type)irqn);
    status = 0;
  } else {
    status = -1;
  }
 
  return (status);
}

int32_t IRQ_Disable ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: 0 on success, -1 on error.

This function disables forwarding of the corresponding interrupt to the CPU.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_Disable (IRQn_ID_t irqn) {
  int32_t status;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    GIC_DisableIRQ ((IRQn_Type)irqn);
    status = 0;
  } else {
    status = -1;
  }
 
  return (status);
}

int32_t IRQ_Enable ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: 0 on success, -1 on error.

This function enables forwarding of the corresponding interrupt to the CPU.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_Enable (IRQn_ID_t irqn) {
  int32_t status;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    GIC_EnableIRQ ((IRQn_Type)irqn);
    status = 0;
  } else {
    status = -1;
  }
 
  return (status);
}

int32_t IRQ_EndOfInterrupt ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: 0 on success, -1 on error.

This function informs the interrupt controller that the interrupt service routine processing of the currently active interrupt request is completed.

The parameter irqn should specify the value previously returned by the IRQ_GetActiveIRQ or IRQ_GetActiveFIQ functions.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_EndOfInterrupt (IRQn_ID_t irqn) {
  int32_t status;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    GIC_EndInterrupt ((IRQn_Type)irqn);
 
    if (irqn == 0) {
      IRQ_ID0 = 0U;
    }
 
    status = 0;
  } else {
    status = -1;
  }
 
  return (status);
}

IRQn_ID_t IRQ_GetActiveFIQ ( void )

Returns: interrupt ID number.

This function retrieves the interrupt ID number of current FIQ source and acknowledges the interrupt.

For Arm GIC the default implementation looks like the following example:

IRQn_ID_t IRQ_GetActiveFIQ (void) {
  // FIQ is not supported, return invalid ID
  return ((IRQn_ID_t)-1);
}

IRQn_ID_t IRQ_GetActiveIRQ ( void )

Returns: interrupt ID number.

This function retrieves the interrupt ID number of current IRQ source and acknowledges the interrupt.

For Arm GIC the default implementation looks like the following example:

IRQn_ID_t IRQ_GetActiveIRQ (void) {
  IRQn_ID_t irqn;
 
  irqn = (IRQn_ID_t)GIC_AcknowledgePending();
 
  return (irqn);
}

uint32_t IRQ_GetEnableState ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: 0 - interrupt is disabled, 1 - interrupt is enabled.

This function retrieves the interrupt enable status of the interrupt identified by the irqn parameter.

Interrupt enable status can be either disabled (0) or enabled (1). Disabled status is returned for interrupts which cannot be identified by irqn.

For Arm GIC the default implementation looks like the following example:

uint32_t IRQ_GetEnableState (IRQn_ID_t irqn) {
  uint32_t enable;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    enable = GIC_GetEnableIRQ((IRQn_Type)irqn);
  } else {
    enable = 0U;
  }
 
  return (enable);
}

IRQHandler_t IRQ_GetHandler ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: registered interrupt handler function address.

This function retrieves address of the interrupt handler callback function corresponding to the specified interrupt ID number.

For Arm GIC the default implementation looks like the following example:

IRQHandler_t IRQ_GetHandler (IRQn_ID_t irqn) {
  IRQHandler h;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    h = IRQTable[irqn];
  } else {
    h = (IRQHandler_t)0;
  }
 
  return (h);
}

uint32_t IRQ_GetMode ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: current interrupt mode configuration with optional IRQ_MODE_ERROR bit set.

This function retrieves interrupt mode configuration of the interrupt identified by the irqn parameter. IRQ_MODE_ERROR is returned for interrupts which cannot be identified by irqn.

For Arm GIC the default implementation looks like the following example:

uint32_t IRQ_GetMode (IRQn_ID_t irqn) {
  uint32_t mode;
  uint32_t val;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    mode = IRQ_MODE_TYPE_IRQ;
 
    // Get trigger mode
    val = GIC_GetConfiguration((IRQn_Type)irqn);
 
    if ((val & 2U) != 0U) {
      // Corresponding interrupt is edge triggered
      mode |= IRQ_MODE_TRIG_EDGE;
    } else {
      // Corresponding interrupt is level triggered
      mode |= IRQ_MODE_TRIG_LEVEL;
    }
 
    // Get interrupt CPU targets
    mode |= GIC_GetTarget ((IRQn_Type)irqn) << IRQ_MODE_CPU_Pos;
 
  } else {
    mode = IRQ_MODE_ERROR;
  }
 
  return (mode);
}

uint32_t IRQ_GetPending ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: 0 - interrupt is not pending, 1 - interrupt is pending.

This function retrieves the pending status of the interrupt identified by the irqn parameter.

Interrupt pending status can be either not pending (0) or pending (1). Not pending status is returned for interrupts which cannot be identified by irqn.

For Arm GIC the default implementation looks like the following example:

uint32_t IRQ_GetPending (IRQn_ID_t irqn) {
  uint32_t pending;
 
  if ((irqn >= 16) && (irqn < IRQ_GIC_LINE_COUNT)) {
    pending = GIC_GetPendingIRQ ((IRQn_Type)irqn);
  } else {
    pending = 0U;
  }
 
  return (pending & 1U);
}

uint32_t IRQ_GetPriority ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: current interrupt priority value with optional IRQ_PRIORITY_ERROR bit set.

This function retrieves the priority of the interrupt identified by the irqn parameter.

The valid priority value can be from zero (0) to the value of IRQ_PRIORITY_Msk. IRQ_PRIORITY_ERROR bit is set in returned value for interrupts which cannot be identified by irqn.

For Arm GIC the default implementation looks like the following example:

uint32_t IRQ_GetPriority (IRQn_ID_t irqn) {
  uint32_t priority;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    priority = GIC_GetPriority ((IRQn_Type)irqn);
  } else {
    priority = IRQ_PRIORITY_ERROR;
  }
 
  return (priority);
}

uint32_t IRQ_GetPriorityGroupBits ( void )

Returns: current number of MSB bits included in the group priority field comparison with optional IRQ_PRIORITY_ERROR bit set.

This function retrieves the number of MSB bits used to determine whether a pending interrupt has sufficient priority to preempt a currently active interrupt.

IRQ_PRIORITY_ERROR value is returned when priority grouping is not supported.

For Arm GIC the default implementation looks like the following example:

uint32_t IRQ_GetPriorityGroupBits (void) {
  uint32_t bp;
 
  bp = GIC_GetBinaryPoint() & 0x07U;
 
  return (7U - bp);
}

uint32_t IRQ_GetPriorityMask ( void )

Returns: current priority masking threshold value with optional IRQ_PRIORITY_ERROR bit set.

This function retrieves the priority masking threshold for the current processor.

IRQ_PRIORITY_ERROR value is returned if priority masking is not supported.

For Arm GIC the default implementation looks like the following example:

uint32_t IRQ_GetPriorityMask (void) {
  return GIC_GetInterfacePriorityMask();
}

int32_t IRQ_Initialize ( void )

Returns: 0 on success, -1 on error.

This function initializes interrupt controller.

It disables all interrupt sources, clears all pending interrupts, sets interrupt priorities to highest priority and configures priority mask to lowest priority. IRQ and FIQ signal lines should be enabled and all interrupt handlers should be set to NULL.

For Arm GIC the default implementation looks like the following example:

#ifndef IRQ_GIC_LINE_COUNT
#define IRQ_GIC_LINE_COUNT      (1020U)
#endif
 
static IRQHandler IRQTable[IRQ_GIC_LINE_COUNT] = { 0U };
 
int32_t IRQ_Initialize (void) {
  uint32_t i;
 
  for (i = 0U; i < IRQ_GIC_LINE_COUNT; i++) {
    IRQTable[i] = (IRQHandler)NULL;
  }
  GIC_Enable();
  return (0);
}

int32_t IRQ_SetHandler	(	IRQn_ID_t	irqn,
		IRQHandler_t	handler
	)

Parameters

[in]	irqn	interrupt ID number
[in]	handler	interrupt handler function address

Returns: 0 on success, -1 on error.

This function registers address of the interrupt handler callback function corresponding to the specified interrupt ID number.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_SetHandler (IRQn_ID_t irqn, IRQHandler_t handler) {
  int32_t status;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    IRQTable[irqn] = handler;
    status =  0;
  } else {
    status = -1;
  }
 
  return (status);
}

int32_t IRQ_SetMode	(	IRQn_ID_t	irqn,
		uint32_t	mode
	)

Parameters

[in]	irqn	interrupt ID number
[in]	mode	mode configuration

Returns: 0 on success, -1 on error.

This function configures the interrupt triggering mode, type, secure access and target CPUs of the interrupt (see IRQ Mode Bit-Masks) identified by the irqn parameter.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_SetMode (IRQn_ID_t irqn, uint32_t mode) {
  int32_t status;
  uint32_t val;
  uint8_t cfg;
  uint8_t secure;
  uint8_t cpu;
 
  status = 0;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    // Check triggering mode
    val = (mode & IRQ_MODE_TRIG_Msk);
    if (val == IRQ_MODE_TRIG_LEVEL) {
      cfg = 0x00U;
    } else if (val == IRQ_MODE_TRIG_EDGE) {
      cfg = 0x02U;
    } else {
      status = -1;
    }
 
    // Check interrupt type
    val = mode & IRQ_MODE_TYPE_Msk;
 
    if (val != IRQ_MODE_TYPE_IRQ) {
      status = -1;
    }
 
    // Check interrupt domain
    val = mode & IRQ_MODE_DOMAIN_Msk;
 
    if (val == IRQ_MODE_DOMAIN_NONSECURE) {
      secure = 0;
    } else {
      // Check security extensions support
      val = GIC_DistributorInfo() & (1UL << 10U);
 
      if (val != 0U) {
        // Security extensions are supported
        secure = 1;
      } else {
        status = -1;
      }
    }
 
    // Check interrupt CPU targets
    val = mode & IRQ_MODE_CPU_Msk;
 
    if (val == IRQ_MODE_CPU_ALL) {
      cpu = 0xFF;
    } else {
      cpu = val >> IRQ_MODE_CPU_Pos;
    }
 
    // Apply configuration if no mode error
    if (status == 0) {
      GIC_SetConfiguration((IRQn_Type)irqn, cfg);
      GIC_SetTarget       ((IRQn_Type)irqn, cpu);
 
      if (secure != 0U) {
        GIC_SetGroup ((IRQn_Type)irqn, secure);
      }
    }
  }
 
  return (status);
}

int32_t IRQ_SetPending ( IRQn_ID_t irqn )

Parameters

[in] irqn interrupt ID number

Returns: 0 on success, -1 on error.

This function sets the pending status of the interrupt identified by the irqn parameter.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_SetPending (IRQn_ID_t irqn) {
  int32_t status;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    GIC_SetPendingIRQ ((IRQn_Type)irqn);
    status = 0;
  } else {
    status = -1;
  }
 
  return (status);
}

int32_t IRQ_SetPriority	(	IRQn_ID_t	irqn,
		uint32_t	priority
	)

Parameters

[in]	irqn	interrupt ID number
[in]	priority	interrupt priority value

Returns: 0 on success, -1 on error.

This function sets the priority of the interrupt identified by the irqn parameter.

Higher priority numbers have lower priority. The highest interrupt priority has priority value 0, while the lowest value depends on the number of implemented priority levels.

The number of implemented priority bits can be determined by setting value IRQ_PRIORITY_Msk to arbitrary irqn and by retrieving the actual stored value with IRQ_GetPriority function.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_SetPriority (IRQn_ID_t irqn, uint32_t priority) {
  int32_t status;
 
  if ((irqn >= 0) && (irqn < IRQ_GIC_LINE_COUNT)) {
    GIC_SetPriority ((IRQn_Type)irqn, priority);
    status = 0;
  } else {
    status = -1;
  }
 
  return (status);
}

int32_t IRQ_SetPriorityGroupBits ( uint32_t bits )

Parameters

[in] bits number of MSB bits included in the group priority field comparison

Returns: 0 on success, -1 on error.

This function sets the number of MSB priority bits used to determine whether a pending interrupt has sufficient priority to preempt a currently active interrupt.

The number of implemented group priority bits can be determined by setting value IRQ_PRIORITY_Msk and by retrieving the actual stored value with IRQ_GetPriorityGroupBits function. Function returns error status -1 if priority grouping is not supported.

For Arm GIC the default implementation looks like the following example:

int32_t IRQ_SetPriorityGroupBits (uint32_t bits) {
  int32_t status;
 
  if (bits == IRQ_PRIORITY_Msk) {
    bits = 7U;
  }
 
  if (bits < 8U) {
    GIC_SetBinaryPoint (7U - bits);
    status = 0;
  } else {
    status = -1;
  }
 
  return (status);
}

int32_t IRQ_SetPriorityMask ( uint32_t priority )

Parameters

[in] priority priority masking threshold value

Returns: 0 on success, -1 on error.

This function sets the priority masking threshold for the current processor.

It ensures that only interrupts with a higher priority than priority threshold value are signaled to the target processor. Function returns error status -1 if priority masking is not supported.

For Arm GIC the default implementation looks like the following example:

IRQ_SetPriorityMask (uint32_t priority) {
  GIC_SetInterfacePriorityMask (priority);
  return (0);
}

Content

Functions

Description

Function Documentation