Interrupts

The arduino library has two widely known functions noInterrupts() and interrupts() to control the firing of interrupts in critical sections of code. Beneath the hood these are assembly instructions like so:

// this is noInterrupts()
# define cli()  __asm__ __volatile__ ("cli" ::: "memory")

// this is interrupts()
# define sei()  __asm__ __volatile__ ("sei" ::: "memory")

both cli() and sei() can be used in arduino code.

In TinyGo we have finer control of interrupts using the runtime/interrupt library.

import "runtime/interrupt"

func main() {
    state := interrupt.Disable()
    // what you want to do with interrupts disabled
    interrupt.Restore(state)
    // interrupts are enabled again (if they were enabled before `interrupt.Disable()`
}

This allows us to nest critical code without fear of accidentally clearing an interrupt in the calling function. state := interrupt.Disable() is equal to noInterrupts() and interrupt.Restore(state) is equal to interrupts(). This prevents hard to debug problems that would happen if we were using cli() and sei().

Below is an example of a program that is unsafe to use with cli() and sei() but is safe to use with the interrupt library.

func foo() {
    state := interrupt.Disable()
    // do something with interrupts disabled
    interrupt.Restore(state)
}
func main() {
    state := interrupt.Disable()
    // do something with interrupts disabled
    foo()
    // do something more, with interrupts still disabled (!)
    interrupt.Restore(state)
}

State should be treated as an opaque number. On AVR state contains the SREG register while on other platforms it could be 0 or 1 depending on whether interrupts were previously disabled or not.