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46 lines
2.2 KiB
Markdown
46 lines
2.2 KiB
Markdown
# Function definitions
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Syntax:
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`[segment (<segment>)] [<modifiers>] <return_type> <name> ( <params> ) [@ <address>] { <body> }`
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`[segment (<segment>)] asm <return_type> <name> ( <params> ) @ <address> extern`
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* `<segment>`: segment name; if absent, then defaults to `default_code_segment` as defined for the platform
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* `<modifiers>`: zero or more of the following:
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* `asm` – the function is written in assembly, not in Millfork (obligatory for `extern` functions),
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see [Using assembly within Millfork programs#Assembly functions](./assembly.md#assembly-functions)
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* `macro` – the function is a macro,
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see [Macros_and inlining#Macros](../abi/inlining.md#macros)
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* `inline` – the function should preferably be inlined
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see [Macros_and inlining#Inlining](../abi/inlining.md#automatic_inlining.md)
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* `noinline` – the function should never be inlined
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* `interrupt` – the function is a hardware interrupt handler.
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You are not allowed to call such functions directly.
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The function cannot have parameters and the retrn type should be `void`.
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* `kernal_interrupt` – the function is an interrupt handler called from a generic vendor-provider hardware interrupt handler.
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The hardware instruction handler is assumed to have preserved the CPU registers,
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so this function only has to preserve the zeropage pseudoregisters.
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An example is the Commodore 64 interrupt handler that calls the function at an address read from $314/$315.
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Unline hardware handlers with `interrupt`, you can treat functions with `kernal_interrupt` like normal functions.
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* `<return_type>` is a valid return type, see [Types](./types.md)
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* `<params>` is a comma-separated list of parameters, in form `type name`. Allowed types are the same as for local variables.
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* `<address>` is a constant expression that defines where in the memory the function is or will be located.
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* `extern` is a keyword than marks functions that are not defined in the current program,
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but are likely to be available at certain address in memory.
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Such functions should be marked as written in assembly and should have their parameters passed through registers.
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* `<body>` is a newline-separated list of either Millfork or assembly statements
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