[Matt Krass]

Originally Posted by intellec7

If you want to generate a pulswidth of 0 - period (0-100%) I generally used Timer 1 because it has to Output Compare Units (A and B).
The code that I use to set up is in asm, because I'm an assembler junkie.
<SNIP!>

:sigh: it's ugly, and inificient, but it did the job for me. If anything IM me or PM me.

Might I recommend the use of [ code] and [ /code] tags?

;Init Timers
;Timer 1 16 bit 2 output compare to drive motors


	ldi		temp,0b10110001 ;Clear OC1A/OC1B on compare match, set at top
	out		TCCR1A,temp		;PWM Phase Correct 8bit

	ldi		temp,0b00000001	;prescaler is 1
	out		TCCR1B,temp

The way I have it, it does not generate interupts, the Atmega hardware has two pins, OC1A and OC1B, this allows you to do 16 bit pwm on two channels.
If you want to control RC servos, which are a PWM wave with the PWM from anywhere from .5 ms to 2.5 ms every ~50 hz (20 ms) then I have a pretty inefficient code, but it gets the job done. BTW this is all using a 16mHz crystal.

;Timer 0 (to call servo routine every 10 ms
	
	ldi		temp,0b00001101
	out		TCCR0,temp	;set prescaler to 1024 and clear timer on compare match

	ldi		temp,0b00000010
	out		TIMSK, temp	;generate an interupt on compare match 16mhz/1024/156=100 hz
	
	ldi		temp,156
	out 	OCR0, temp
	;we want to execute the actual servo subroutine 50 hz, but the timer
	;doesnt go that slow, so we call the servo every 100 hz, and only execute 
	;the code every other call

I first have a timer that calls an adress every 10 ms, but in the actual subroutine it only executes the code every even call.

Servo: ;update servo positions, should call every 20ish ms called by interupt
	push	temp
	push    temp2
	in		temp, SREG
	push	temp
	
	dec		ServoSt		;this is to activatre the routine only every other interupt 
	tst		ServoSt		;since it is called every 10ms
	brne	Servexit
		
	ldi		ServoSt, 2
	clr		ServCoun
	sbi		Servport,Serv1	; Servport is the port and Serv1 is the pin
	sbi		Servport,Serv2
	sbi		Servport,Serv3
	sbi		Servport,Serv4
;	rcall	Delay200	;this is to optomize the range of the servo
	rcall	Delay200	;to 255, because no servo signal should ever be
	rcall	Delay200    ;less than ~400-600 us
	ser		temp		;this is to execute the below code for 2 ms then leave

Serloop:
	dec		ServCoun 	;servo counter, is decremented ~ every 7.5 us
Ser1:
	cp		ServCoun,Servo1	;sees if the servo counter is more or = to the
	brsh	Ser2			;desired servo value
	cbi		Servport,Serv1
	nop						;an attempt to make it equal if servo is met or not
Ser2:
	cp		ServCoun,Servo2
	brsh	Ser3
	cbi		Servport,Serv2
	nop
Ser3:
	cp		ServCoun,Servo3
	brsh	Ser4
	cbi		Servport,Serv3
	nop
Ser4:
	cp		ServCoun,Servo4
	brsh	Ser5
	cbi		Servport,Serv4
	nop
Ser5:
 	;continue if more servos
	
	rcall	Delay7
	dec		temp
	brne	Serloop

ServExit:
	pop		temp
	out		SREG,temp
	pop		temp2
	pop		temp
	reti

Delay7:
; each cycle =  62.5 ns (16 MHz)
; number of processor cycle = 112 = 40 uS
; total delay ~7 useconds 
	;clr DelayCounter1	;1 (A)
	ldi DelayCounter1, 35	;
DelayLoop2:					;
	dec DelayCounter1	;60 x 1 (B)
	brne DelayLoop2		;1 x 1 if no branch (C), 255 x 2 if branch (D)
						;        (A)  (B)   (D)  (C)   
						; so far: 1 + 60 + 118 + 1 = 180 cycles * 62.5ns
						;                             
						; 1 + N + (N-1)*2 + 1 = 1 + 3N -2 + 1 = 3N 
						; N=213 --> 40 uS	
	ret

Delay200:
	ldi	DelayCounterMS, 5 ;40*5=200 useconds
Delay200msloop:
	call Delay40
	dec DelayCounterMS
	brne Delay200msloop
	ret
 (note Delay200 depends on Delay40!!)

Delay40:
; each cycle =  62.5 ns (16 MHz)
; number of cycle = 213 = 40 uS (not processor cycles)
; total delay 40 useconds (slightly less)
	;clr DelayCounter1	;1 (A)
	ldi DelayCounter1, 210	;1 (was 213, 210 tuned with Locic Analy)
DelayLoop1:					;
	dec DelayCounter1	;256 x 1 (B)
	brne DelayLoop1		;1 x 1 if no branch (C), 255 x 2 if branch (D)
						;        (A)  (B)   (D)  (C)   
						; so far: 1 + 256 + 510 + 1 = 768 cycles * 270 ns --> 207 useconds
						;                             768        * 62.5   -->  48 useconds
						; 1 + N + (N-1)*2 + 1 = 1 + 3N -2 + 1 = 3N 
						; N=213 --> 40 uS
	ret