A C++ template library for embedded applications
Designed and maintained by
Aster Consulting Ltd

etl::function

These templates are designed to enable easy creation of callbacks to global, static and class member functions without
the caller having to know which type actually it is.

etl::function    
Callback to free or member functions taking zero or one parameter.
Function pointer at runtime.

etl::function_fv
Callback to a free function taking no parameters.
Function pointer at compile time.

etl::function_fp
Callback to a free function taking one parameter.
Function pointer at compile time.

etl::function_mv
Callback to a member function taking no parameters.
Function pointer at compile time.

etl::function_imv
Callback to a member function taking no parameters.
Instance reference and function pointer at compile time.

etl::function_mp
Callback to a member function taking one parameter.
Function pointer at compile time.

etl::function_imp
Callback to a member function taking one parameter. 
Instance reference and function pointer at compile time.

Instances of any of these types may be passed as pointers or references to etl::ifunction.

One use that is applicable to embedded platforms is to use them connect interrupt vectors to class member handling
functions. Particularly useful when the code is applicable to multiple targets devices.

The template is designed in such a way that the caller does not need to be aware of the type of the callee.

The caller declares an instance of etl::function or one of its variants. The caller defines a pointer or reference to
an etl::ifunction. This pointer or reference will be initialised with the instance defined in the caller.

Example


The following code can be found in

examples\FunctionInterruptSimulation


The interrupt vector table contains entries for three timer timeouts and two uart character rx handlers. These are
vectored to normal static functions.

void Timer1TimeoutInterrupt();
void Timer2TimeoutInterrupt();
void Timer3TimeoutInterrupt();
void Uart1RxInterrupt();
void Uart2RxInterrupt();

The timer timeout interrupts are handled by an instance of the class Timer and the free function
FreeTimerInterruptHandler. The UART Rx interrupts are handled by instances of the class Uart.

Timer1 interrupts call the member function of an instance of Timer.
Timer2 interrupts call the static member function of Timer.
Timer3 interrupts call the free function  FreeTimerInterruptHandler.
UART1 interrupts call the member function of instance 1 of Uart.
UART1 interrupts call the member function of instance 2 of Uart.

#include <iostream>
#include <iomanip>

#include "function.h"

//********************************
// Fake UART Rx register.
//********************************
char get_char()
{
  static char c = 'A';
  return c++;
}

//********************************
// Interrupt vectors & callbacks.
//********************************
// Callback interfaces.
// Note that they do not require any knowledge about the callee apart from the parameter type.
etl::ifunction<void>* timer1_callback;   // A pointer to a callback taking no parameters.
etl::ifunction<void>* timer2_callback;   // A pointer to a callback taking no parameters.
etl::ifunction<void>* timer3_callback;   // A pointer to a callback taking no parameters.
etl::ifunction<char>* uart1_rx_callback; // A pointer to a callback taking a char parameter.
etl::ifunction<char>* uart2_rx_callback; // A pointer to a callback taking a char parameter.

extern "C"
{
// Function called from the timer1 interrupt vector.
void Timer1Interrupt()
{
  (*timer1_callback)();
}

// Function called from the timer2 interrupt vector.
void Timer2Interrupt()
{
  (*timer2_callback)();
}

// Function called from the timer3 interrupt vector.
void Timer3Interrupt()
{
  (*timer3_callback)();
}

// Function called from the UART1 rx interrupt vector.
void Uart1RxInterrupt()
{
  (*uart1_rx_callback)(get_char());
}

// Function called from the UART2 rx interrupt vector.
void Uart2RxInterrupt()
{
  (*uart2_rx_callback)(get_char());
}
}

//********************************
// Timer driver.
//********************************
class Timer
{
public:

  // Constructor.
  Timer()
  {
  }

  // Handler for interrupts from the timer.
  void MemberTimerInterruptHandler()
  {
    std::cout << "Timer interrupt (member)\n";
  }

  // Static handler for interrupts from the timer.
  static void StaticTimerInterruptHandler()
  {
    std::cout << "Timer interrupt (static)\n";
  }
};

//********************************
// Free function timer driver.
//********************************
void FreeTimerInterruptHandler()
{
  std::cout << "Timer interrupt (free)\n";
}

etl::function_fv<FreeTimerInterruptHandler> free_callback;

//********************************
// UART driver.
//********************************
class Uart
{
public:

  // Constructor.
  Uart(int port_id)
    : port_id(port_id)
  {
  }

  // Handler for rx interrupts from the UART.
  void RxInterruptHandler(char c)
  {
    std::cout << "UART" << port_id << " Rx char interrupt : Received '" << c << "'\n";
  }

  int port_id;
};

// Declare the driver instances.
Timer timer;
Uart  uart1(0);
Uart  uart2(1);

etl::function_imv<Timer, timer, &Timer::MemberTimerInterruptHandler> timer_member_callback;
etl::function_fv<&Timer::StaticTimerInterruptHandler>                timer_static_callback;
etl::function_imp<Uart, char, uart1, &Uart::RxInterruptHandler>      uart1_callback;
etl::function_imp<Uart, char, uart2, &Uart::RxInterruptHandler>      uart2_callback;

//********************************
// Test it out.
//********************************
int main()
{

  // Setup the callbacks.
  timer1_callback   = &timer_member_callback;
  timer2_callback   = &timer_static_callback;
  timer3_callback   = &free_callback;
  uart1_rx_callback = &uart1_callback;
  uart2_rx_callback = &uart2_callback;

  // Simulate the interrupts.
  Timer1Interrupt();
  Timer2Interrupt();
  Timer3Interrupt();
  Uart1RxInterrupt();
  Uart2RxInterrupt();

  return 0;
}