;
; hello9.step.asm
; Neil Gershenfeld CBA MIT 11/12/05
;

.include "tn13def.inc"
.equ rxpin = PB4

.def temp0 = R16
.def temp1 = R17
.def temp2 = R18
.def temp3 = R19
.def byte = R20
.def motion_set = R21
.def bitcnt = R22

.equ on_count = 30
.equ off_count = 10
.equ pulse_count = 10

.cseg
.org 0
rjmp reset

;
; getchar
; assumes no line driver (doesn't invert bits)
;

getchar:
   ldi bitcnt,9 ; 8 data bit + 1 stop bit
   getchar1:
      sbis PINB, rxpin ; wait for start bit
     rjmp getchar1
   rcall bit_delay ; 0.5 bit delay
  getchar2:
      rcall bit_delay ; 1 bit delay
      rcall bit_delay ;
      clc ; clear carry
      sbis PINB, rxpin ; if RX pin high skip
         sec ; otherwise set carry
      dec bitcnt
      breq getchar3 ; return if all bits read
      ror byte ; otherwise shift bit into receive byte
      rjmp getchar2 ; go get next bit
   getchar3:
      ret
;
; bit delay
;
.equ b = 17 ; 9600 bps
bit_delay:
   ldi temp3, b
   bitloop:
      dec temp3
      brne bitloop
   ret

pulse_0:
   ldi temp0, pulse_count
   loop0_0:
      ldi temp1, pulse_count
      loop0_1:
         ldi temp2, on_count
         sbi PORTB, PB0
         on0:
            dec temp2
  	    brne on0
         ldi temp2, off_count
         cbi PORTB, PB0
         off0:
            dec temp2
 	    brne off0
         dec temp1
         brne loop0_1
      dec temp0
      brne loop0_0
   ret

pulse_1:
   ldi temp0, pulse_count
   loop1_0:
      ldi temp1, pulse_count
      loop1_1:
         ldi temp2, on_count
         sbi PORTB, PB1
         on1:
            dec temp2
  	    brne on1
         ldi temp2, off_count
         cbi PORTB, PB1
         off1:
            dec temp2
 	    brne off1
         dec temp1
         brne loop1_1
      dec temp0
      brne loop1_0
   ret

pulse_2:
   ldi temp0, pulse_count
   loop2_0:
      ldi temp1, pulse_count
      loop2_1:
         ldi temp2, on_count
         sbi PORTB, PB2
         on2:
            dec temp2
  	    brne on2
         ldi temp2, off_count
         cbi PORTB, PB2
         off2:
            dec temp2
 	    brne off2
         dec temp1
         brne loop2_1
      dec temp0
      brne loop2_0
   ret

pulse_3:
   ldi temp0, pulse_count
   loop3_0:
      ldi temp1, pulse_count
      loop3_1:
         ldi temp2, on_count
         sbi PORTB, PB3
         on3:
            dec temp2
  	    brne on3
         ldi temp2, off_count
         cbi PORTB, PB3
         off3:
            dec temp2
 	    brne off3
         dec temp1
         brne loop3_1
      dec temp0
      brne loop3_0
   ret

step_right:
   rcall pulse_2
   rcall pulse_0
   rcall pulse_1
   rcall pulse_3
   ret

step_left:
   rcall pulse_2
   rcall pulse_3
   rcall pulse_1
   rcall pulse_0
   ret

reset:
   ldi temp0, low(RAMEND) ; set stack pointer to top of RAM
   out SPL, temp0 ;
   sbi DDRB, PB0 ; set output pins
   sbi DDRB, PB1
   sbi DDRB, PB2
   sbi DDRB, PB3      
   loop:
      rcall getchar
      ldi motion_set,4
      cp motion_set, byte
	  brne loop
      rcall step_right
      rcall step_right
      rcall step_right
      rcall step_right
      rcall step_right
      rcall step_right
      rcall step_right
      rcall step_right
      ;rcall step_left
      ;rcall step_left
      ;rcall step_left
      ;rcall step_left
      ;rcall step_left
      ;rcall step_left
      ;rcall step_left
      ;rcall step_left
      rjmp loop