; Send a pulsed 38 kHz stream to provide a IR output for
; detection by a IR demodulator like used in remote control
; applications.
;
; 11/27/98 Brian Hammill
;
;
; IRED is controlled by PB7 - Common Emitter NPN Transistor drives LED.
; IR Detector/Demodulator idles in high state and is connected
; to PD5
; An optional visible LED is on PB4 for debugging/indicating.
; The IRED is "on" when PB7 is high.
; First pass will just modulate the LED so we can test xmit.
; I use idle mode to hopefully cut power consumption between LED pulses.
;
; This code should work in the 90S1200 or 90S2323/43.  It would be
; possible to use a lower clock frequency too.  I used the 2313 and 3.6864 MHz Xtal
; because that is what I had.
;
; This code is provided as-is without warranty and is placed in the public domain
; so that it might demonstrate some of the coding requirements of the AVR controller.
; Brian Hammill - hammill@ipass.net December 1998.
; http://www.ipass.net/~hammill

.include "2313def.inc

; The Interrupt Vectors

reset:	rjmp	startup
	reti		; ext int 0 (not used)
	reti		; ext int 1 (not used)
	reti		; timer1 not used
	reti		;
	reti		;
	rjmp	timer0
	reti		; UART RRF Not Used
	reti            ; UART TRE Not Used	
	reti		; UART TRDE Not Used 
	reti		; analog comparator not used

; Code we need to execute at startup.

startup:
	; setup timer0 for 10 mS period. ck/1024

	ldi R16, $05
	out TCCR0, R16
	ldi R16, (256 - 15)
	out TCNT0, R16 ; 3.6864/1024)/36 = 100 Hz
	; must init the stack.
	; initialize stack pointer
	ldi	R16, RAMEND
	out	SPL,R16
	; initialize the data direction registers
	ldi	R16, 144
	out	DDRB, R16 
	; enable timer interrupts
	ldi	R16,$02	; enable timer 0 interrupts
	out	TIMSK,R16
	ldi	R16, 0; enable IDLE mode for sleep.
	out	MCUCR, R16
	
	sei	; globally enable interrupts
	sleep	; should be able to sleep until timer overflows	
mainloop:
	; loop and wait for an interrupt
	nop
	nop
	rjmp mainloop
; need to send several cycles of 38 kHz every 10 mS.

timer0:	; Interrupt service routine gets executed when
	; timer 0 expires.
	ldi R16, (256 - 34 )
	out TCNT0, R16	; reset the counter

	; now do the IR send

	; IRED connected on portb bit 7
	
	ldi R17, $20	; number of pulses
	; 38 kHz has period of 26.3 uS
	; turn LED on for 26.3 uS
pulse:
	sbi	PORTB, 7	; Turn on LED
	rcall	delay1		; Wait 13 uS
	cbi	PORTB, 7	; Turn off LED (IR)
	rcall	delay1		; wait 13 uS
	dec R17
	brne	pulse
	sleep	; back to sleep until another interrupt?
	reti


delay1: ; This is a 13 uS delay.  Takes 97 instructions
	ldi R16, 13	; was 23
	nop		; add 1 clock to total delay
delay1_0:
	dec R16
	brne delay1_0	
	ret