Initialize TIM2 Channel 2 for PWM Output in Assembly

[shaw205k]

Posted on March 15, 2014 at 04:00

Hello,

I have a STM32F100RB discovery board and I am trying to setup up TIM2 Channel 2 to output a PWM signal using assembly language, but I am having trouble sorting through the reference manual. The code I have so far to initialize the TIM2 registers is below. This code is part of a larger program that works, so I know my TIM2 initialization is the problem. If someone can point out where I have went wrong it would be greatly appreciated!

;TIM2 - Base Addr: 0x4000 0000

TIM2_CR1 EQU 0x40000000 ; TIM1 Control Register 1

TIM2_CR2 EQU 0x40000004 ; TIM1 Control Register 2

TIM2_SMCR EQU 0x40000008 ; TIM1 Slave Mode Control Register

TIM2_DIER EQU 0x4000000C ; TIM1 DMA/Interrupt Enable Register

TIM2_SR EQU 0x40000010 ; TIM1 Status Register

TIM2_EGR EQU 0x40000014 ; TIM1 Event Generation Register

TIM2_CCMR1 EQU 0x40000018 ; TIM1 Compare/Capture Mode Register 1

TIM2_CCMR2 EQU 0x4000001C ; TIM1 Compare/Capture Mode Register 2

TIM2_CCER EQU 0x40000020 ; TIM1 Compare/Capture Enable Register

TIM2_CNT EQU 0x40000024 ; TIM1 Counter

TIM2_PSC EQU 0x40000028 ; TIM1 Prescaler

TIM2_ARR EQU 0x4000002C ; TIM1 Auto-reload Register

TIM2_RCR EQU 0x40000030 ; TIM1 Repetition Counter Register

TIM2_CCR1 EQU 0x40000034 ; TIM1 Capture/Compare Register 1

TIM2_CCR2 EQU 0x40000038 ; TIM1 Capture/Compare Register 2

TIM2_CCR3 EQU 0x4000003C ; TIM1 Capture/Compare Register 3

TIM2_CCR4 EQU 0x40000040 ; TIM1 Capture/Compare Register 4

TIM2_BDTR EQU 0x40000044 ; TIM1 Break and Dead-time Register

TIM2_DCR EQU 0x40000048 ; TIM1 DMA Control Register

TIM2_DMAR EQU 0x4000004C ; TIM1 DMA Address Register

;Registers for config and enabling the clocks

;Use Reset and Clock Control Register (RCC) base address = 0x40021000

RCC_APB2ENR EQU 0X40021018

RCC_APB1ENR EQU 0X4002101C

clock_init   ;Enable peripheral clocks for various ports and subsystems

ldr R6,=RCC_APB2ENR

mov R0, #0x00000A1D ;Enable Alt Fcn IO, GPIO ABC, ADC1, and TIM1

str R0,[R6]

ldr R6,=RCC_APB1ENR

mov R0, #0x00000001 ;Enable TIM2 Clock

str R0,[R6]

gpio_init

ldr R6,= GPIOA_CRL

ldr R0,= 0x4444BBB4 ;A1, A2, A3 are alt fcn (PWM) 

str R0,[R6]

tim2_init

ldr R6, = TIM2_CR1

mov R0, #0x01 ;set CEN bit high to start up system

str R0, [R6]

ldr R6, = TIM2_EGR

mov R0, #0x01 ;initialize registers

str R0, [R6]

ldr R6, = TIM2_CCMR1

mov R0, #0x6C00 ;set OC2M = 110 and OC2PE = 1 and OCPFE = 1

str R0, [R6]

ldr R6, = TIM2_CCER

mov R0, #0x0001 ;CC2E = 1

str R0, [R6]

ldr R6, = TIM2_PSC

mov R0, #799 ;divide value to get 10kHz clock into counter

str R0, [R6]

ldr R6, = TIM2_ARR

mov R0, #200 ;Period so that it is 20ms

str R0, [R6]

ldr R6, = TIM2_CCR2

mov R0, #100 ;PW value 

str R0, [R6]

ldr R6, = TIM2_CR1

mov R0, #0x01 ;set CEN bit high to start up system

str R0, [R6]

main PROC

;other code that works...

B main

ENDP

[Tesla DeLorean]

Posted on March 15, 2014 at 14:33

799? 8 MHz processor?

20 ms from 10 KHz, 200 - 1

You probably want to configure the speed/direction of the pins.

[shaw205k]

Posted on March 17, 2014 at 02:18

Yes the processor is set to 8MHz, and thanks for the adjustment on the period.

When I set the CC2E bit in the TIM2_CCER register I left the CC2P bit (in the same register) as zero to set the polarity to active high. Is this what you mean by the direction of the pin?

When you refer to setting the speed of the pin are you referring to the Mode bits that are set when I write to the GPIOB_CRH register? When I write to this register I set the PWM output pin to output mode with a max speed of 50MHz. I can't find any other register that refers to the speed of the pin.