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1.1 KiB
1.1 KiB
Interfacing with external code
Calling external functions at a static address
To call an external function, you need to declare it as asm extern
. For example:
asm void putchar(byte a) @$FFD2 extern
The function parameter will be passed via the accumulator, the function itself is located in ROM at $FFD2. A call like this:
putchar(13)
will be compiled to something like this on 6502:
LDA #13
JSR $FFD2
For more details about how to pass parameters to asm
functions, see:
-
for 6502: Using 6502 assembly within Millfork programs#Assembly functions.
-
for Z80: Using Z80 assembly within Millfork programs#Assembly functions.
Calling external functions at a dynamic address
To call a function that has its address calculated dynamically, you just need to do the same as what you would do in assembly; 6502 example:
asm void call_function(byte a) {
JMP (function_address)
}
where function_address
is a variable that contains the address of the function to call.