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55 lines
1.4 KiB
Markdown
55 lines
1.4 KiB
Markdown
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[< back to index](../index.md)
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# Millfork calling convention
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**Note:** all the info below may change without any warning and is given only for debugging purposes.
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## 6502
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#### Parameters:
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* if the function has one parameter of size one byte, it is passed via the A register
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* otherwise, all parameters are passed via static locations
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#### Return values:
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* one-byte return values are passed via the A register
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* two-byte return values are passed via the A (low byte) and X (high byte) register
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#### Register preservation:
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* callee may clobber all three registers (A, X, Y) and most flags (Z, V, C, N, and also I if using inline assembly)
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* callee expects the D flag to be clear and will leave it clear
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* on 65816: callee will preserve the emulation flag
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(setting the emulation flag correctly is the responsibility of the initialization code)
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* on 65816 in native mode:
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* callee expects the M and X flag to be set and will leave them set
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(8-bit accumulator and index registers by default)
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* callee expects the direct page register to be set to 0000 and will not change it
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## Z80
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#### Parameters:
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* all parameters are passed via static locations
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#### Return values:
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* one-byte return values are passed via the A register
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* two-byte return values are passed via the HL register pair
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#### Register preservation:
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* callee may clobber all flags
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* callee may clobber all registers except for IX, IY and shadow registers
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