Interrupt Service Routines

An interrupt can occure any time. Interrupts are handled with standard forth words. They must not have any stack effect.

The interrupt forth word is executed within the context of the current user area and stack frame. Using throw is not recommended since it will affect the user area of the interrupted task.

+int ( – )

enable the interrupt handling globally

-int ( – )

disable the interrupt handling globally

int@ ( n – XT )

fetch the XT of the interrupt service routine for interrupt n

int! (XT n – )

store the XT as the handler for interrupt n. This has immediate effect.

int-trap ( n – )

simulate interrupt n

Interrupts are processed in two stages. First stage is a simple low-level processing routine. The low-level generic interrupt routine stores the index of the interrupt in a CPU register.

The inner interpreter checks every time it is entered the register for a non-Null value. If it is set the interrupt processing routine is activated. It uses the interrupt number and calculates the index into an platform specific table (AVR uses the EEPROM, the MSP430 the index flash).