;
; hello.echo.44.asm
;
; 115200 baud serial echo and LED hello-world program
;
; Neil Gershenfeld
; CBA MIT 10/12/09
;
; (c) Massachusetts Institute of Technology 2009
; Permission granted for experimental and personal use;
; license for commercial sale available from MIT.
;

.include "tn44def.inc"

.equ led_pin = PB2; LED pin
.equ led_port = PORTB; LED port
.equ led_dir = DDRB; LED dir
.equ txpin = PA6; transmit pin
.equ rxpin = PA7; receive pin
.equ comm_port = PORTA; comm port
.equ comm_dir = DDRA; comm direction
.equ comm_pins = PINA; comm pins
.def bitcnt = R16; bit counter
.def temp = R17; temporary storage
.def temp1 = R18; temporary storage
.def txbyte = R19; transmit byte
.def rxbyte = R20; receive byte

.equ button_port = PORTA ; button port (note same as comm)
.equ button_dir = DDRA ; pin direction (note same as comm)
.equ button_pin = PA3; button
.equ pina_ins = PINA ; input pins

;
; print
; 
.macro print
   ldi zl,low(@0*2)
   ldi zh,high(@0*2)
   rcall print_db
   .endmacro

.cseg
.org 0
rjmp reset

;
; half_bit_delay
; serial half bit delay
;
half_bit_delay:
   ldi temp, 25; 115200 baud (20 MHz clock /1)
   half_bit_delay_loop:
      dec temp
      brne half_bit_delay_loop
   ret
;
; putchar
; assumes no line driver (doesn't invert bits)
;
;putchar:
;   ldi bitcnt, 10; 1 start + 8 data + 1 stop bit
;   com txbyte; invert everything
;   sec; set start bit
;   putchar0:
;      brcc putchar1; if carry set
;      sbi comm_port, txpin; send a '0'
;      rjmp putchar2; else	
;   putchar1:
;       cbi comm_port, txpin	; send a '1'
;       nop; even out timing
;   putchar2:
;       rcall half_bit_delay; bit delay
;       rcall half_bit_delay; " 
;       lsr txbyte; get next bit
;       dec bitcnt; if not all bits sent
;       brne putchar0; send next bit
;   ret;
;
;
; blink_delay
; LED blink delay
;
blink_delay:
   ldi temp, 255
   blink_delay_loop:
      ldi temp1, 255
      blink_delay_loop1:
         dec temp1
         brne blink_delay_loop1
      dec temp
      brne blink_delay_loop
   ret
;
; blink
; blink the LED
;
blink:
   sbi led_port, led_pin
   rcall blink_delay
   cbi led_port, led_pin
   ret
;
; print_db
; prints a null-terminated .db string
;
;print_db:
;   print_loop:
;      lpm
;      mov txbyte,R0
;      cpi txbyte,0
;      breq return
;      rcall putchar
;      adiw zl, 1
;      rjmp print_loop
;   return:
;      ret
	  
getButton:
	sbic pina_ins, button_pin ; check if button is low
	 rjmp getButton
getButtonRel:
	sbis pina_ins, button_pin ; don't proceed until button released and pin pulled back up
	 rjmp getButtonRel
	ret

toggleLED:
	ldi temp, 1 ; temp is what the bit is set at
	sbic pina_ins, led_pin ; if bit is set yay, if not, don't skip and set it to zero
	 ldi temp, 0

	cbi led_port, led_pin  ; should be zero going to 1
	sbrc temp, 0	; if temp == 1 skip (or if temp !=1 execute (i.e. temp == 0))
	 sbi led_port, led_pin ; zero goes to one
	ret ; LED toggled!
	
;
; main program
;
reset:
   ;
   ; set fuse low byte to 0x7E for 20 MHz resonator
   ;
   ; set clock divider to /1
   ;
   ldi temp, (1 << CLKPCE)
   ldi temp1, (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0)
   out CLKPR, temp
   out CLKPR, temp1
   ;
   ; set stack pointer to top of RAM
   ;
   ldi temp, high(RAMEND)
   out SPH, temp
   ldi temp, low(RAMEND)
   out SPL, temp
   ;
   ; init comm pin
   ;
   sbi comm_port, txpin
   sbi comm_dir, txpin
   ;
   ; init LED pins
   ;
   cbi led_port, led_pin
   sbi led_dir, led_pin
   ;
   ; init Button pins
   ; going from b00 so no transitions need to be worried about but we clear anyway
   cbi button_port, button_pin ; clear pin empty
   cbi button_dir,  button_pin ; set direction to input (zero)
   sbi button_port, button_pin ; pull pini-up
   ;
   ; start main loop
   ;
   
   loop:
      rcall getButton
;     sbis pina_ins, led_pin
	  sbi led_port, led_pin	
;      rcall toggleLed
      rcall getButton
;      sbis pina_ins, led_pin
	  cbi led_port, led_pin

;      cbi led_port, led_pin
;      rcall blink
      rjmp loop