Chief Delphi - ATMEGA16 PWM

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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/p...ts/doc2466.pdf

thank you in advanced,
John

Re: ATMEGA16 PWM

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.

Re: ATMEGA16 PWM

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"

Re: ATMEGA16 PWM

Quote:

Originally Posted by sparksandtabs

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. (That link is for C++, but it's the same idea in C.)

Re: ATMEGA16 PWM

Quote:

Originally Posted by sparksandtabs

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.

Quote:

What compiler do you use?

I use avr-gcc on Linux

Quote:

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.

Quote:

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:

Code:

#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.

Re: ATMEGA16 PWM

Code:

 ;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.

Code:

;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.

Code:

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:

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!!)

Code:

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]

Re: ATMEGA16 PWM

Quote:

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?

Code:

;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

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

Re: ATMEGA16 PWM

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?