Test different wasy of setting the I bit in SREG on AVR

iBitTest.s

; Test if instruction after I bit in SREG is set is always run
; More info at http://wp.josh.com/2016/01/05/different-ways-to-set-i-bit-in-avr-sreg-besides-sei/

	jmp start			// Reset vector

	.org INT0addr

INT0_handler:

loop1:
	//sbi PORTB,5			// LED on . Uncommend this to verifiy that the ISR even gets called.

    rjmp loop1			// Infinite loop

	// INT0 is the only vector used, so mind as well start code here...

start:


	#if 0			// Use this to try an find where the lost byte gets pushed when SP points to mem mapped IO registers

		; Fill all of memory with the pattern 0x55 so I can see where the push is ending up
		; (It turns out that it ended up nowheres)

			.equ    memstrt = 0x100           ; First address of RAM to be filled
			.equ    memend  = 0x4FF           ; Last address of RAM to be filled
			.equ    fillchr = 0x55            ; Fill pattern

		;---------------------------------------------------------------------------
		; Fills RAM with 0x55
		fillmem:
				ldi     XL,low(SRAM_START); Load the X pointer with start address
				ldi     XH,high(SRAM_START)	  ;
 
				ldi     r16,0x55          ; Load fill pattern to r16

		fill_lp:
				st      X+,r16            ; Store a fill pattern, advance X pointer
				cpi     XL,low(RAMEND+1)  ; Repeat until XL = low(memend+1)
				brne    fill_lp           ;

				cpi     XH,high(RAMEND+1) ; Repeat until XH = high(memend+1)
				brne    fill_lp           ; (executed only on every 256th loop cycle)

		;---------------------------------------------------------------------------


	#endif

	sbi DDRB,5			// LED pin to output mode

	sbi DDRD,2			// INT0 to output mode
	sbi PORTD,2			// INT0 high

	sbi EIMSK, INT0		// Enable INT0 interrupt on low

	cbi PORTD, 2		// Trigger INT0 interrupt

	// Ok, gun is loaded - just sei to fire an interrupt!

	// Test bed: Put some code here that turns on the I bit


	// SEI (base case)
	#if 1
		sei
	#endif 

	// ST 
	#if 0
		clr r29        // Clear Y pointer high byte
		ldi r28,0x5f   // Set Y low byte to point to SREG (0x3f+0x20)
		ld r16, Y      // Get SREG
		ori r16,128    // Set I bit 
		st Y,r16       // Put SREG in the Doug Henning way
	#endif 

	// Point stack to SREG
	#if 0
		clr r28       // ZERO
		out 0x3e, r28 // Stack high   
		ldi r28,0x5f  // pointer to memory mapped SREG
		out 0x3d, r28 // Stack now points to SREG!

		ldi r16,0x80
		push r16
	#endif

	// Point stack to GPIO1
	#if 0
		clr r28       // ZERO
		out 0x3e, r28 // Stack high   
		ldi r28, 0x4a // pointer to memory mapped GPIOR1
		out 0x3d, r28 // Stack now points to SREG!

		ldi r16,0x80
		push r16
	#endif

	// XCH
	#if 0
		clr r31        // Clear Z pointer high byte
		ldi r20,0x5f   // Set Z low byte to point to SREG (0x3f+0x20)
		ld r16, Z      // Get SREG
		ori r16,128    // Set I bit 
		xch Z,r16       // Put SREG in the Doug Henning way
	#endif 

//	nop					// Uncomment this to test the negative case. The nop will consume the preveledged instruction so we shoudl never rea the next one.
	sbi PORTB,5			// LED on 

loop:	
	jmp loop			// Infinate loop