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Function definitions

Syntax:

[segment (<segment>)] [<modifiers>] <return_type> <name> ( <params> ) [@ <address>] { <body> }

[segment (<segment>)] asm <return_type> <name> ( <params> ) @ <address> extern

  • <segment>: segment name; if absent, then defaults to default_code_segment as defined for the platform

  • <modifiers>: zero or more of the following:

    • asm – the function is written in assembly, not in Millfork (obligatory for extern functions), see Using assembly within Millfork programs#Assembly functions

    • macro – the function is a macro, see Macros_and inlining#Macros

    • inline – the function should preferably be inlined see Macros_and inlining#Inlining

    • noinline – the function should never be inlined

    • interrupt – the function is a hardware interrupt handler. You are not allowed to call such functions directly. The function cannot have parameters and the return type should be void.

    • kernal_interrupt – the function is an interrupt handler called from a generic vendor-provider hardware interrupt handler. The hardware instruction handler is assumed to have preserved the CPU registers, so this function only has to preserve the zeropage pseudoregisters. An example is the Commodore 64 interrupt handler that calls the function at an address read from $314/$315. Unlike hardware handlers with interrupt, you can treat functions with kernal_interrupt like normal functions.

  • <return_type> is a valid return type, see Types

  • <params> is a comma-separated list of parameters, in form type name. Allowed types are the same as for local variables.

  • <address> is a constant expression that defines where in the memory the function is or will be located.

  • extern is a keyword than marks functions that are not defined in the current program, but are likely to be available at certain address in memory. Such functions should be marked as written in assembly and should have their parameters passed through registers.

  • <body> is a newline-separated list of either Millfork or assembly statements