ATMEGA16 PWM

[John Gutmann]

Ok so here is my problem,

I have a AVR ATMEGA16 uC made by atmel. I have normal timers working but I cannot figure out from the data sheet how to get a PWM output. I have posted on avrfreaks.net but none will post an example code for me. All they do is redirect me to ode that is not for my uC. So i decided since I know a few people on here use them if they could post some very basic example code for me which just includes basic PWM timer operation and to have to code commented so I can look at it and learn from it.

The datasheet can be found at:
http://www.atmel.com/dyn/resources/prod_documents/doc2466.pdf

thank you in advanced,
John

[Don Reid]

Here is a pwm module I wrote. It is currently set up for an ATMega8, so the register names may need to be changed slightly, but I have used a version of this code on an ATMega16.

This does direct motor control PWM, 0 - 100%, not RC servo PWM. If that is what you want, you need to adjust the period and limit the range.

[John Gutmann]

Usually from what I have seen for the atmegax series you can use any code from a lower processor on a higher level processor with out changing register names. I don't know if it is true but I guess I can try your code and find out.

What compiler do you use?
I am currently running AVR studio-GCC

I am going to look at some things but do you think it will be safe to hook the servo up to the STK500.

wow....that is above my reading level. If possible seeing as how I am a begginer would you mind commenting some, I mean most of that code. I have never seen the #endif and all those # commands before other than #include and #define Could you possible offer an explanation?

Also I need "main.h" and "stdint.h"

[Tristan Lall]

wow....that is above my reading level. If possible seeing as how I am a begginer would you mind commenting some, I mean most of that code. I have never seen the #endif and all those # commands before other than #include and #define Could you possible offer an explanation?Compiler directives (http://www.cplusplus.com/doc/tutorial/preprocessor.html). (That link is for C++, but it's the same idea in C.)

[Don Reid]

Usually from what I have seen for the atmegax series you can use any code from a lower processor on a higher level processor with out changing register names. I don't know if it is true but I guess I can try your code and find out.

When a newer processor add resources the register names may change, for example with one UART there is UBRRL, but with 2 UARTS there is UBRR0L and UBRR1L.

What compiler do you use?
I use avr-gcc on Linux

I am going to look at some things but do you think it will be safe to hook the servo up to the STK500.
I don't think a 5V logic signal can hurt a servo even if it doesn't like the timing. The power to the servo needs to come from a source that can supply enough current.

wow....that is above my reading level. If possible seeing as how I am a begginer would you mind commenting some, I mean most of that code. I have never seen the #endif and all those # commands before other than #include and #define Could you possible offer an explanation?

Also I need "main.h" and "stdint.h"

The #ifdefs include or don't include parts of the code for different purposes. the SIM set creates a version that runs on a workstation and simulates the behavior. The pwm simulation isn't very interesting, it just returns the setting multiplied by a constant. The PWM_INT set causes an interrupt every cycle.

You should look at the register settings this code does, and look at the manual sections for those registers to understand how it uses the timer to do PWM. Then you can write you own code or modify this to do what you want.

main.h isn't very much:

#define F_CPU 14745600UL

extern int direction; // 1 = right side, -1 = left side (reverse)


stdint.h is part of the standard C library. It came with avr-gcc. You can do without it by changing "uint8_t" to "unsigned char" etc.

[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.

;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

I swear it looks prettier in the text editor.
all of the names temp, temp2, Serloop, ServSt, Servo1- 4 are all registers. To change the servo position change the value of Servo1-4.

AND one more thing, Delay200, Delay7 are two delay loops. Their code:

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

:sigh: it's ugly, and inificient, but it did the job for me. If anything IM me or PM me.
[Edit for code tags, thanks Matt Krass]

[Matt Krass]

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

[John Gutmann]

Do you happen to have anything in C? Just a quick and easy code that will show me how to do it.

What should my timer be set at? 8mhz I am guess to get the most efficient use of your processor.

What Timer should I use?

What is the easiest way to run 2 servos at once?