97 lines
2.1 KiB
ArmAsm
97 lines
2.1 KiB
ArmAsm
; RAMEND is pretty self explanatory.
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.equ RAMEND, 0x08FF
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; Check [1] and [2] for more info about the following three
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; symbols
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.equ SREG, 0x3F
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.equ SPL, 0x3D
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.equ SPH, 0x3E
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; Check [3] for more info about the following three symbols.
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.equ PORTB, 0x05
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.equ DDRB, 0x04
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.equ PINB, 0X03
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.org 0x0000
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rjmp MAIN
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MAIN:
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; Reset system status. Check this link for more details:
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; http://www.rjhcoding.com/avr-asm-sreg.php [1]
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clr r16
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out SREG, r16
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; Initialize stack pointer. Put the low byte of RAMEND in SPL (Stack Pointer Low)
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; and the high byte in SPH (Stack Pointer High). Check this link for more details:
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; http://www.rjhcoding.com/avr-asm-functions.php [2]
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ldi r16, lo8(RAMEND)
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out SPL, r16
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ldi r16, hi8(RAMEND)
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out SPH, r16
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; Set port bits to output mode. We will use BUILTIN_LED, so we need to set
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; the fifth bit in DDRB (Data Direction Register B). Check this link for
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; more details:
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; https://web.ics.purdue.edu/~jricha14/Port_Stuff/PortB_general.htm [3]
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;
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; Also an important thing to note is that PORTB handles digital PINs from
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; 8 to 13 so by setting the fifth bit of DDRB actually sets PIN 13 for
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; output:
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; https://www.arduino.cc/en/Reference/PortManipulation
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ldi r16, 0x20
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out DDRB, r16
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; In the main loop we will toggle the fifht bit in PORTB to turn the LED on and off
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; using exclusive or. After that we will wait for some time because we won't be able
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; to see the LED blink otherwise.
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ldi r17, 0x20
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clr r16
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MAINLOOP:
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eor r16, r17
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out PORTB, r16
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call WAIT
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rjmp MAINLOOP
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WAIT:
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push r16
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push r17
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push r18
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; Loop 0x400000 times which takes approximately 12 milion cycles which is
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; approximately 0.7s. For cycles/instruction info check this link, this is
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; actually the AVR Instruction Set Manual:
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; http://ww1.microchip.com/downloads/en/devicedoc/atmel-0856-avr-instruction-set-manual.pdf [4]
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ldi r16, 0x20
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ldi r17, 0x00
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ldi r18, 0x00
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_WAIT:
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dec r18
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brne _WAIT
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dec r17
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brne _WAIT
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dec r16
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brne _WAIT
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pop r18
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pop r17
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pop r16
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ret
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