GCBASIC documentation
Interrupts

Introduction

Interrupts are a feature of many microcontrollers. They allow the microcontroller to temporarily pause (interrupt) the code it is running and then start running another piece of code when some event occurs. Once it has dealt with the event, it returns to where it was and continues running the program.

Many events can trigger an interrupt, such as a timer reaching its limit, a serial message being received, or a special pin on the microcontroller receiving a signal.

Using Interrupts

There are two ways to use interrupts in GCBASIC. The first way is to use the On Interrupt command. This automatically enables a given interrupt, and runs a particular subroutine when the interrupt occurs.

The other way to deal with interrupts is to create a subroutine called Interrupt. GCBASIC calls this subroutine whenever an interrupt occurs, and your code can then check the "flag" bits to determine which interrupt has occurred, and what should be done about it. If you use this approach, you will need to enable the desired interrupts manually. It is also essential that your code clears the flag bits, or the interrupt routine will be called repeatedly.

A combination of these two methods is also possible — the code generated by On Interrupt will check to see if the interrupt is one it recognises. If the interrupt is recognised, On Interrupt deals with it; if not, the Interrupt subroutine is called to deal with the interrupt.

The recommended approach is to use On Interrupt, since it is both more efficient and easier to set up.

During some sections of code, it is desirable not to have any interrupts occur. In this case, use the IntOff command to disable interrupts at the start of the section, and IntOn to re-enable them at the end. If any interrupt events occur while interrupts are disabled, they will be processed as soon as interrupts are re-enabled. If the program does not use interrupts, IntOn and IntOff are removed automatically by GCBASIC.

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