[cc65] 6502.h

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From: Piotr Fusik (P.Fusik_at_elka.pw.edu.pl)
Date: 2003-01-07 10:44:08 

Hi!

Here're my comments (marked >>>):

6502.h:

#define F_IEN  	   	0x04	/* I flag */

>>> What's 'IEN' ? I is the 'Interrupt Disable' flag.

/* Function to call any machine language subroutine. All registers in the
 * regs structure are passed into the routine and the results are passed
 * out. Some of the flags are ignored on input. The called routine must
 * end with an RTS.
 */
void __fastcall__ _sys (struct regs* r);

>>> Which flags are ignored? Why?

_sys.c:

; Get and assign X and Y

	iny
	lda	(ptr1),y
	tay
	iny
	lda	(ptr1),y
	tay

>>> There should be tax in place of first tay.

	and	#%11001011

>>> Bits 4 and 5 are ignored by plp on 6502, but not on 65816, I think.
>>> I'm not sure about other CPUs.
>>> Enabling interrupts is not a good idea IMHO.

Piotr

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