Interrupt Handling

interrupt_handling Interrupt Handling in NetBurner Applications

interrupt_overview Overview

An interrupt is a hardware or software signal that temporarily suspends normal program execution to handle a time-critical event. When an interrupt occurs, the processor:

1. Saves the current execution context
2. Executes the Interrupt Service Routine (ISR)
3. Restores the context and resumes normal execution

Normal Program Flow          Interrupt Flow
─────────────────            ──────────────
 
    Instruction A                Instruction A
          |                            |
          v                            v
    Instruction B            ┌──────────────────┐
          |                  │ Interrupt Signal │
          v                  └──────────────────┘
    Instruction C                      |
          |                            v
          v                  ┌─────────────────┐
    Instruction D            │  Save Context   │
                             └─────────────────┘
                                      |
                                      v
                             ┌─────────────────┐
                             │   Execute ISR   │
                             └─────────────────┘
                                      |
                                      v
                             ┌─────────────────┐
                             │ Restore Context │
                             └─────────────────┘
                                      |
                                      v
                                Instruction B
                                      |
                                      v
                                Instruction C
                                      |
                                      v
                                Instruction D

interrupt_sources Common Interrupt Sources

NetBurner devices handle interrupts from various sources:

• Hardware Timers - Periodic or one-shot timing events
• Serial Ports - UART data reception/transmission
• Ethernet Controllers - Network packet events
• GPIO Pins - External hardware signals
• Software Traps - Programmatically triggered interrupts

interrupt_platform_variations Platform Variations

Interrupt handling implementation varies by processor architecture:

Platform	Complexity	Key Characteristics
ARM (Cortex-M7)	Simple	Direct function calls, minimal setup
ColdFire (MCF5441x)	Complex	Requires entry/exit macros, controller setup

NetBurner provides abstraction layers to simplify interrupt configuration across all platforms.

---

core_interrupt_functions Core Interrupt Functions

The following functions work across all NetBurner platforms and provide a consistent interface for interrupt management.

interrupt_header_requirements Header Requirements

#include <pins.h>        // For PinIO objects
#include <system.h>      // For interrupt functions

interrupt_function_overview Function Overview

Interrupt Configuration Workflow
────────────────────────────────
 
  ┌─────────────────────────────────┐
  │  1. Configure Pin as Interrupt  │
  │     SetPinIrq(pin, pol, func)   │
  └─────────────────────────────────┘
                 |
                 v
  ┌─────────────────────────────────┐
  │    2. Enable the Interrupt      │
  │        EnableIrq(pin)           │
  └─────────────────────────────────┘
                 |
                 v
  ┌─────────────────────────────────┐
  │  Interrupt Active - ISR Called  │
  └─────────────────────────────────┘
                 |
                 v
  ┌─────────────────────────────────┐
  │   3. Disable When Finished      │
  │        DisableIrq(pin)          │
  └─────────────────────────────────┘

interrupt_setpinirq SetPinIrq() - Configure Interrupt Pin

Function Signature:**

bool SetPinIrq(PinIO pin, int polarity, PinIrq_t func);

Parameters:**

Parameter	Type	Description
pin	PinIO	Pin object to configure as interrupt source
polarity	int	Trigger condition (see polarity table below)
func	PinIrq_t	Function pointer to the ISR

Polarity Values:**

Signal Polarity Configuration
─────────────────────────────
 
 Value  │  Trigger Type          │  Signal Diagram
────────┼────────────────────────┼─────────────────────
   2    │  High Level            │  ────┐
        │                        │      └──────
────────┼────────────────────────┼─────────────────────
   1    │  Rising Edge (Pos)     │      ┌─────
        │                        │  ────┘
────────┼────────────────────────┼─────────────────────
   0    │  Any Edge (Both)       │      ┌─────    ────┐
        │                        │  ────┘     or      └──
────────┼────────────────────────┼─────────────────────
  -1    │  Falling Edge (Neg)    │  ────┐
        │                        │      └─────
────────┼────────────────────────┼─────────────────────
  -2    │  Low Level             │      ┌──────
        │                        │  ────┘

Returns:** true if configuration successful, false otherwise.

Example:**

// ISR function
void MyButtonISR() {
    // Handle button press
    printf("Button pressed!\r\n");
}
 
// Configure pin 23 for falling edge interrupt
PinIO buttonPin(23);
buttonPin.function(PINMODE_GPIO);
SetPinIrq(buttonPin, -1, MyButtonISR);

interrupt_enableirq EnableIrq() - Activate Interrupt

Function Signature:**

void EnableIrq(PinIO pin);

Enables interrupt processing for the specified pin.

Example:**

EnableIrq(buttonPin);  // Start receiving interrupts

interrupt_disableirq DisableIrq() - Deactivate Interrupt

Function Signature:**

void DisableIrq(PinIO pin);

Disables interrupt processing for the specified pin.

Example:**

DisableIrq(buttonPin);  // Stop receiving interrupts

---

isr_restrictions ISR Restrictions

isr_critical_constraints Critical Constraints

The code within an ISR executes in an interrupt context, which has strict limitations. The following operations are PROHIBITED in an ISR:

ISR Execution Context
─────────────────────
 
  User Application                    Interrupt Context
  ────────────────                    ─────────────────
  
  ┌──────────────┐                    ┌──────────────┐
  │              │                    │              │
  │  Full RTOS   │                    │  Limited     │
  │  Services    │  <───────X────>    │  Services    │
  │  Available   │     Cannot         │  Available   │
  │              │      Call          │              │
  └──────────────┘                    └──────────────┘
  
  Can use:                            Can use:
  - OSxxPend                          - OSxxPendNoWait only
  - malloc/free                       - Direct hardware access
  - printf/write                      - OSxxPost
  - All I/O                           - Simple variables

isr_prohibited_rtos Prohibited RTOS Functions

All blocking/waiting functions are forbidden:**

// NEVER call these in an ISR:
OSMboxPend()          // Mailbox wait
OSSemPend()           // Semaphore wait
OSQPend()             // Queue wait
OSCritEnter()         // Critical section entry
OSChangePrio()        // Priority change
OSTaskDelete()        // Task deletion
OSLock()              // Scheduler lock
OSUnlock()            // Scheduler unlock
OSTaskCreate()        // Task creation
OSTimeDly()           // Time delay

Allowed RTOS operations (non-blocking only):**

// Safe to call in ISR:
OSMboxPendNoWait()    // Non-blocking mailbox check
OSSemPendNoWait()     // Non-blocking semaphore check
OSQPendNoWait()       // Non-blocking queue check
OSMboxPost()          // Post to mailbox
OSSemPost()           // Post to semaphore
OSQPost()             // Post to queue

isr_prohibited_io Prohibited I/O Functions

All I/O operations that may block are forbidden:**

// NEVER call these in an ISR:
write()               // File/socket write
writeall()            // Complete write
read()                // File/socket read
printf()              // Formatted output
fprintf()             // File formatted output
fdprintf()            // Descriptor formatted output
printf()             // Integer formatted output
scanf()               // Formatted input
gets()                // Line input
puts()                // String output

isr_prohibited_memory Prohibited Memory Functions

Dynamic memory operations are forbidden:**

// NEVER call these in an ISR:
malloc()              // Allocate memory
free()                // Free memory
new                   // C++ allocation
delete                // C++ deallocation

isr_recommended_pattern Recommended ISR Pattern

// Correct ISR Implementation
volatile bool eventFlag = false;
volatile uint32_t eventData = 0;
 
// ISR: Minimal processing, set flag
void MyISR() {
    // Read hardware register
    eventData = ReadHardwareRegister();
    
    // Set flag for main loop
    eventFlag = true;
    
    // Optional: Signal task via semaphore
    OSSemPost(&processingTask);
}
 
// Main task: Handle event
void ProcessingTask(void* pd) {
    while (1) {
        OSSemPend(&processingTask, 0);
        
        if (eventFlag) {
            eventFlag = false;
            
            // Now safe to use all functions
            ProcessEvent(eventData);
            printf("Event processed: %lu\r\n", eventData);
        }
    }
}

---

platform_specific_implementations Platform-Specific Implementations

Different processor architectures require different interrupt setup procedures.

Platform Interrupt Architecture
────────────────────────────────
 
         NetBurner Platforms
                 |
     ┌───────────┴───────────┐
     |                       |
     v                       v
  ARM Based            ColdFire Based
  ─────────            ──────────────
     |                       |
     |                       |
     v                       v
┌─────────┐            ┌──────────┐
│ SAME70  │            │ MCF5441x │
└─────────┘            └──────────┘
     |                       |
     v                       v
Simple Config          Complex Config
- Direct ISR           - INTERRUPT macro
- Port priority        - SetIntc() setup
- PinIO based          - Vector tables

---

same70_platforms SAME70 Platforms (MODM7AE70 and SBE70LC)

same70_architecture Architecture Overview

The SAME70 (Cortex-M7) features:

• Any GPIO pin can be used as an interrupt source
• Port-based priority - all pins on same port share priority
• 7 Priority Levels - 1 (highest) to 7 (lowest)

SAME70 Interrupt Structure
──────────────────────────
 
  Physical Pins              Port IRQ Controller
  ─────────────              ───────────────────
  
  ┌──────┐                   ┌─────────────────┐
  │ PA0  │───┐               │                 │
  │ PA1  │───┤               │   PIOA IRQ      │
  │ PA2  │───┤──────────────>│  Priority: X    │
  │ ...  │   │               │                 │
  │ PA31 │───┘               └─────────────────┘
  └──────┘                            |
                                      v
  ┌──────┐                   ┌─────────────────┐
  │ PB0  │───┐               │                 │
  │ PB1  │───┤               │   PIOB IRQ      │
  │ PB2  │───┤──────────────>│  Priority: Y    │
  │ ...  │   │               │                 │
  │ PB31 │───┘               └─────────────────┘
  └──────┘                            |
                                      v
  ┌──────┐                   ┌─────────────────┐
  │ PC0  │───┐               │                 │
  │ PC1  │───┤               │   PIOC IRQ      │
  │ PC2  │───┤──────────────>│  Priority: Z    │
  │ ...  │   │               │                 │
  │ PC31 │───┘               └─────────────────┘
  └──────┘

same70_port_priority Port Priority Configuration

SetPortIrqPriority() - By PinIO Object

Function Signature:**

bool SetPortIrqPriority(PinIO pin, int priority);

Parameters:**

Parameter	Type	Description
pin	PinIO	Any pin on the target port
priority	int	Priority level: 1 (highest) to 7 (lowest)

Important:** Setting priority for any pin affects the entire port.

Returns:** true if successful, false otherwise.

Example:**

PinIO myPin(23);  // Pin on PIOB
SetPortIrqPriority(myPin, 3);  // All PIOB interrupts now priority 3

SetPortIrqPriority() - By Port Number

Function Signature:**

bool SetPortIrqPriority(int portNum, int priority);

Parameters:**

Parameter	Type	Description
portNum	int	Port number: PIOA=0, PIOB=1, PIOC=2, PIOD=3, PIOE=4
priority	int	Priority level: 1 (highest) to 7 (lowest)

Example:**

SetPortIrqPriority(1, 3);  // Set PIOB to priority 3

same70_port_mapping Port Priority Mapping

SAME70 Port Assignments
───────────────────────
 
Port Number  │  Port Name  │  Example Usage
─────────────┼─────────────┼──────────────────────
     0       │    PIOA     │  High priority sensors
     1       │    PIOB     │  Medium priority inputs
     2       │    PIOC     │  Communication signals
     3       │    PIOD     │  General I/O
     4       │    PIOE     │  Low priority monitoring

same70_workflow Configuration Workflow

Critical:** Always set port priority before configuring pin interrupts.

SAME70 Interrupt Setup Sequence
────────────────────────────────
 
  Step 1                        Step 2                        Step 3
  ──────                        ──────                        ──────
  
┌─────────────────┐          ┌─────────────────┐          ┌─────────────────┐
│ Set Port        │          │ Configure Pin   │          │ Enable          │
│ Priority        │   ───>   │ Interrupt       │   ───>   │ Interrupt       │
│                 │          │                 │          │                 │
│ SetPortIrqPri() │          │ SetPinIrq()     │          │ EnableIrq()     │
└─────────────────┘          └─────────────────┘          └─────────────────┘

same70_example Complete SAME70 Example

#include <pins.h>
#include <system.h>
#include <nbrtos.h>
 
// ISR for external sensor
void SensorISR() {
    // Minimal processing in ISR
    OSSemPost(&sensorEvent);
}
 
void ConfigureSensorInterrupt() {
    // Pin 42 is on PIOB (port 1)
    PinIO sensorPin(42);
    sensorPin.function(PINMODE_GPIO);
    
    // Step 1: Set port priority (all PIOB pins)
    SetPortIrqPriority(1, 2);  // High priority (2)
    
    // Step 2: Configure pin interrupt
    SetPinIrq(sensorPin, 1, SensorISR);  // Rising edge trigger
    
    // Step 3: Enable interrupt
    EnableIrq(sensorPin);
    
    printf("Sensor interrupt configured on pin 42\r\n");
}

---

mcf5441x_platforms MCF5441x Platforms (MOD54415, MOD54417, NANO54415 and SB800EX)

mcf5441x_architecture Architecture Overview

The MCF5441x (ColdFire) processor requires more complex setup:

• INTERRUPT() macro - Handles ISR entry/exit code
• SetIntc() function - Configures interrupt controller hardware
• 7 Priority Levels - 1 to 7, with 7 being highest (unmaskable)

ColdFire Interrupt Flow
───────────────────────
 
  Interrupt Source              Interrupt Controller           ISR Processing
  ────────────────              ────────────────────           ──────────────
  
  ┌──────────┐                  ┌─────────────────┐            ┌───────────┐
  │  UART 0  │                  │                 │            │           │
  │ Vector:26│──┐               │  Controller 0   │            │  MACRO    │
  └──────────┘  │               │                 │            │  Handles  │
                ├───────────────>   Vector Table  │───────────>│  Entry/   │
  ┌──────────┐  │               │                 │            │  Exit     │
  │  Timer 2 │  │               │  Priority: 1-7  │            │  Code     │
  │ Vector:15│──┘               │                 │            │           │
  └──────────┘                  └─────────────────┘            └───────────┘
                                                                      |
                                                                      v
                                                               ┌───────────┐
                                                               │  User ISR │
                                                               │  Function │
                                                               └───────────┘

mcf5441x_interrupt_macro INTERRUPT() Macro

The INTERRUPT() macro simplifies ISR implementation by handling:

• Saving processor registers
• Setting status register
• RTOS notification
• Restoring registers on exit

Header Requirements

#include <nbrtos.h>     // RTOS functions
#include <cfinter.h>    // ColdFire interrupt support

Macro Syntax

INTERRUPT(FunctionName, SR_Value)
{
    // ISR code here
}

Parameters

Parameter	Description
FunctionName	ISR function name (used with SetIntc())
SR_Value	Status Register value - controls interrupt masking

Status Register Values

The Status Register (SR) controls which interrupts can preempt the current ISR:

ColdFire Status Register Interrupt Masking
──────────────────────────────────────────
 
SR Value  │  Mask Level  │  Allows Interrupts At Level  │  Blocks
──────────┼──────────────┼──────────────────────────────┼─────────────
 0x2000   │      0       │  All (1-7)                   │  None
 0x2100   │      1       │  2 and above                 │  Level 1
 0x2200   │      2       │  3 and above                 │  Levels 1-2
 0x2300   │      3       │  4 and above                 │  Levels 1-3
 0x2400   │      4       │  5 and above                 │  Levels 1-4
 0x2500   │      5       │  6 and above                 │  Levels 1-5
 0x2600   │      6       │  7 only                      │  Levels 1-6
 0x2700   │      7       │  None (masks all maskable)   │  All < 7
 
Note: Level 7 interrupts are unmaskable - they always execute
      Bit 29 is supervisor bit (always set = 0x2000 base)

Interrupt Priority Hierarchy

Interrupt Priority Levels
─────────────────────────
 
Level 7  ───────────  Highest (Unmaskable)
   ^                  Critical system events
   |                  Can interrupt anything
   |
Level 6  ───────────  Very High Priority
   ^                  Time-critical operations
   |
Level 5  ───────────  High Priority
   ^                  Important peripherals
   |
Level 4  ───────────  Medium-High Priority
   ^                  Communication interfaces
   |
Level 3  ───────────  Medium Priority
   ^                  General peripherals
   |
Level 2  ───────────  Low-Medium Priority
   ^                  Non-critical I/O
   |
Level 1  ───────────  Low Priority
   ^                  Background tasks
   |
Level 0  ───────────  Disabled

Level 7 Warning

CRITICAL:** Level 7 interrupts are unmaskable and can interrupt themselves!

Level 7 Interrupt Danger
────────────────────────
 
┌─────────────────┐
│  Level 7 ISR    │
│    Executing    │
└────────┬────────┘
         |
         |  Another Level 7
         |  interrupt occurs
         v
┌─────────────────┐  <─── DANGER!
│  Level 7 ISR    │      Stack corruption
│  Re-enters!     │      Register collision
└─────────────────┘      Data corruption

Mitigation Strategy:**

// Ensure ISR completes before next Level 7 can occur
INTERRUPT(CriticalISR, 0x2700)
{
    // 1. Acknowledge interrupt source immediately
    ClearInterruptFlag();
    
    // 2. Minimal processing only
    volatile uint32_t data = ReadHardwareRegister();
    
    // 3. Set flag for main loop processing
    criticalEventFlag = true;
    
    // Exit quickly - no delays!
}

mcf5441x_setintc SetIntc() Function

Configures the interrupt controller to route hardware interrupts to ISR functions.

Function Declaration

Important:** SetIntc() is defined in platform HAL files and must be declared as extern:

extern void SetIntc(int intcnum, long func, int vector, int level);

Location:** \nburn\platform\MOD5441x\hal.cpp

Parameters

Parameter	Type	Description
intcnum	int	Interrupt controller number (0 or 1 for MCF5441x)
func	long	Pointer to ISR function (from INTERRUPT macro)
vector	int	Interrupt vector number (0-255, device-specific)
level	int	Interrupt priority level (0=disabled, 1-7)

Vector Numbers

The MCF5441x has 256 exception vectors:

• 0-63: Core exceptions (reserved)
• 64-255: Peripheral interrupt sources (192 device-specific vectors)

Common MCF5441x Interrupt Sources
─────────────────────────────────
 
Source       │  Vector  │  Typical Use
─────────────┼──────────┼────────────────────────
UART 0       │    26    │  Serial communication
UART 1       │    27    │  Serial communication
PIT Timer 2  │    15    │  Periodic timer
1-Wire       │    63    │  1-Wire bus interface
Ethernet     │   varies │  Network events

Reference:** See Chapter 17, Table 17.2.9.1 in NXP MCF5441x Reference Manual

Interrupt Controller Selection

MCF5441x Interrupt Controllers
──────────────────────────────
 
Controller 0 (intcnum = 0)        Controller 1 (intcnum = 1)
──────────────────────            ──────────────────────
 
├─ UART 0 (Vector 26)             ├─ Additional peripherals
├─ PIT Timers                     ├─ Extended I/O
├─ Ethernet                       ├─ Communication interfaces
├─ 1-Wire (Vector 63)             └─ Platform-specific devices
└─ Core peripherals

mcf5441x_example Complete MCF5441x Example: 1-Wire Interface

#include <nbrtos.h>
#include <cfinter.h>
#include <sim5441x.h>
 
// Declare external SetIntc function
extern void SetIntc(int intc, long func, int vector, int level);
 
// State tracking
volatile enum { OK, BUSY, ERROR } ow_state = OK;
 
// Actual ISR implementation
void OWMasterIsr()
{
    // Read 1-Wire status
    uint8_t status = sim1.ow.sr;
    
    // Clear interrupt flag
    sim1.ow.sr = status;
    
    // Update state
    if (status & OW_SR_RBF) {
        // Receive buffer full
        ow_state = OK;
    }
}
 
// INTERRUPT macro wrapper - sets SR to mask interrupts below level 6
INTERRUPT(ow_master_int_routine, 0x2600)
{
    OWMasterIsr();
}
 
// Initialization function
void OWInit()
{
    // Configure 1-Wire hardware registers
    sim1.ow.cr  = 0;              // Control register
    sim1.ow.div = 0x7C;           // Divide peripheral clock to 1 MHz
    sim1.ow.cmd = 0;              // Command register
    sim1.ow.ier = OW_IER_ERBF;    // Enable receive buffer full interrupt
    
    // Configure interrupt controller
    // Controller 0, ISR function, Vector 63, Level 3
    SetIntc(0, (long)&ow_master_int_routine, 63, 3);
    
    // Initialize state
    ow_state = OK;
    
    printf("1-Wire interrupt configured: Vector 63, Level 3\r\n");
}
 
// Usage in UserMain()
void UserMain(void *pd)
{
    init();
    
    // Initialize 1-Wire with interrupt support
    OWInit();
    
    while (1) {
        // Application code
        OSTimeDly(TICKS_PER_SECOND);
    }
}

mcf5441x_workflow MCF5441x Configuration Workflow

ColdFire Interrupt Setup Process
────────────────────────────────
 
Step 1: Implement ISR Logic
┌─────────────────────────────┐
│ void MyIsr() {              │
│     // Handle interrupt     │
│ }                           │
└─────────────────────────────┘
              |
              v
Step 2: Wrap with INTERRUPT Macro
┌─────────────────────────────┐
│ INTERRUPT(my_isr, 0x2500) { │
│     MyIsr();                │
│ }                           │
└─────────────────────────────┘
              |
              v
Step 3: Configure Hardware
┌─────────────────────────────┐
│ // Set registers            │
│ peripheral.control = ...;   │
│ peripheral.enable = ...;    │
└─────────────────────────────┘
              |
              v
Step 4: Configure Controller
┌─────────────────────────────┐
│ SetIntc(0,                  │
│   (long)&my_isr,            │
│   vector_num,               │
│   priority_level);          │
└─────────────────────────────┘
              |
              v
Step 5: Interrupt Active
┌─────────────────────────────┐
│   ISR Called on Events      │
└─────────────────────────────┘

mcf5441x_best_practices Best Practices for MCF5441x

1. Always use INTERRUPT() macro - Never write bare ISR functions
2. Match SR value to needs - Don't block higher priority interrupts unnecessarily
3. Initialize hardware first - Set up peripheral registers before SetIntc()
4. Use correct vector numbers - Consult reference manual for device-specific vectors
5. Avoid Level 7 unless critical - Use lower levels when possible

---

somrt1061_platform SOMRT1061 Platform

somrt1061_overview Overview

The SOMRT1061 platform uses the i.MX RT1061 processor (ARM Cortex-M7). Interrupt configuration follows the standard NetBurner approach with some platform-specific considerations.

i.MX RT1061 Interrupt Architecture
──────────────────────────────────
 
     GPIO Pins                    NVIC Controller               ISR
     ─────────                    ───────────────               ───
     
┌──────────────┐                ┌─────────────┐          ┌───────────┐
│  GPIO1[0:31] │───────────────>│             │          │           │
├──────────────┤                │   Priority  │─────────>│  Direct   │
│  GPIO2[0:31] │───────────────>│   Settings  │          │  Function │
├──────────────┤                │             │          │   Call    │
│  GPIO3[0:31] │───────────────>│  IRQ Enable │          │           │
├──────────────┤                │             │          └───────────┘
│  GPIO4[0:31] │───────────────>│  Vector     │
├──────────────┤                │  Routing    │
│  GPIO5[0:31] │───────────────>│             │
└──────────────┘                └─────────────┘

somrt1061_configuration Configuration Approach

The SOMRT1061 uses the standard NetBurner interrupt functions:

#include <pins.h>
#include <system.h>
 
// ISR function
void MyRT1061ISR() {
    // Handle interrupt
}
 
// Configuration
void ConfigureInterrupt() {
    PinIO myPin(23);
    myPin.function(PINMODE_GPIO);
    
    // Standard functions work directly
    SetPinIrq(myPin, 1, MyRT1061ISR);    // Rising edge
    EnableIrq(myPin);
}

somrt1061_notes Platform-Specific Notes

1. No port-based priority - Each GPIO can have individual priority
2. Direct ISR calls - No INTERRUPT() macro needed
3. Fast interrupt response - Cortex-M7 architecture provides low latency
4. Standard PinIO support - All GPIO pins accessible via PinIO objects

somrt1061_example SOMRT1061 Example

#include <init.h>
#include <nbrtos.h>
#include <pins.h>
#include <system.h>
 
const char *AppName = "RT1061 Interrupt Example";
 
// Semaphore for signaling
OS_SEM buttonSem;
 
// Simple ISR - post semaphore
void ButtonPressISR() {
    OSSemPost(&buttonSem);
}
 
// Processing task
void ButtonTask(void *pd) {
    while (1) {
        OSSemPend(&buttonSem, 0);
        printf("Button pressed at %lu seconds\r\n", Secs);
    }
}
 
void UserMain(void *pd) {
    init();
    
    // Initialize semaphore
    OSSemInit(&buttonSem, 0);
    
    // Configure button on pin 23
    PinIO buttonPin(23);
    buttonPin.function(PINMODE_GPIO);
    
    // Setup interrupt for falling edge (button press)
    SetPinIrq(buttonPin, -1, ButtonPressISR);
    EnableIrq(buttonPin);
    
    // Create processing task
    OSTaskCreate(ButtonTask,
                 NULL,
                 (void *)&ButtonTaskStack[USER_TASK_STK_SIZE],
                 (void *)ButtonTaskStack,
                 MAIN_PRIO - 1);
    
    printf("%s: Interrupt configured on pin 23\r\n", AppName);
    
    while (1) {
        OSTimeDly(TICKS_PER_SECOND);
    }
}

---

interrupt_summary Summary and Best Practices

interrupt_cross_platform Cross-Platform Compatibility

For maximum portability across NetBurner platforms:

// Always use these standard functions:
SetPinIrq(pin, polarity, isr_func);    // Configure
EnableIrq(pin);                         // Enable
DisableIrq(pin);                        // Disable

interrupt_platform_selection Platform Selection Guide

Choose Your Approach Based on Platform
──────────────────────────────────────
 
Platform         │  Complexity  │  Key Functions
─────────────────┼──────────────┼────────────────────────────
SAME70           │  Simple      │  SetPinIrq()
(MODM7AE70)      │              │  SetPortIrqPriority()
                 │              │  EnableIrq() / DisableIrq()
─────────────────┼──────────────┼────────────────────────────
MCF5441x         │  Complex     │  INTERRUPT() macro
(MOD54415, etc)  │              │  SetIntc()
                 │              │  Manual register setup
─────────────────┼──────────────┼────────────────────────────
SOMRT1061        │  Simple      │  SetPinIrq()
(i.MX RT1061)    │              │  EnableIrq() / DisableIrq()

interrupt_general_best_practices General Best Practices

1. Keep ISRs short - Minimal processing, set flags, post semaphores
2. Use volatile for shared variables - Prevent compiler optimization issues
3. Never block in ISRs - No waiting, no delays, no blocking I/O
4. Signal tasks for processing - Use semaphores/mailboxes to defer work
5. Test interrupt rates - Ensure ISR completes before next interrupt
6. Document vector/priority choices - Make interrupt configuration clear
7. Initialize hardware before interrupts - Configure peripherals, then enable IRQ

interrupt_debugging Debugging Interrupts

Interrupt Debugging Checklist
─────────────────────────────
 
┌─────────────────────────────────────┐
│ 1. Is ISR being called?             │ <─── Add toggle/LED
│    > Add debug indicator            │
└─────────────────────────────────────┘
              |
              v
┌─────────────────────────────────────┐
│ 2. Is interrupt enabled?            │ <─── Verify EnableIrq()
│    > Check enable status            │
└─────────────────────────────────────┘
              |
              v
┌─────────────────────────────────────┐
│ 3. Is priority correct?             │ <─── Check for blocking
│    > Verify vs other interrupts     │
└─────────────────────────────────────┘
              |
              v
┌─────────────────────────────────────┐
│ 4. Is hardware generating signal?   │ <─── Check with scope
│    > Verify with oscilloscope       │
└─────────────────────────────────────┘
              |
              v
┌─────────────────────────────────────┐
│ 5. Is ISR corrupting data?          │ <─── Check for prohibited
│    > Review ISR restrictions        │      function calls
└─────────────────────────────────────┘

interrupt_error_prevention Error Prevention

// WRONG - Blocking in ISR
void BadISR() {
    OSTimeDly(TICKS_PER_SECOND);  // NEVER!
    printf("Interrupt!\r\n");      // NEVER!
}
 
// CORRECT - Signal and exit
void GoodISR() {
    interruptFlag = true;
    OSSemPost(&processSem);        // Non-blocking post
}

---

interrupt_resources Additional Resources

For more detailed information:

• Platform Hardware Manuals: \nburn\docs\nxp\
• ColdFire Interrupt Header: \nburn\arch\coldfire\include\cfinter.h
• NetBurner API Documentation: SDK API reference
• Example Projects: NetBurner SDK examples directory