Enable PWM timer output on STM32F4 using peripheral library (not STM Cube)

pwm_setup.c

/* Board support headers */
#include "stm32f4xx.h"
#include "stm32f4xx_gpio.h"
#include "stm32f4xx_tim.h"
#include "stm32f4xx_rcc.h"

#define TIMER_BASE_FREQUENCY    72000000

#define PWM_FREQUENCY           40000
#define PWM_TICKS               TIMER_BASE_FREQUENCY/PWM_FREQUENCY
#define PWM_COMPARE_VALUE       PWM_TICKS/2

/**
 * Configure the PWM timer to generate 40kHz
 */
void pwm_timer_setup(void)
{
    // Start up timer and GPIO clocks
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

    // Configure output pin
    GPIO_InitTypeDef GPIO_initstruct;
    GPIO_initstruct.GPIO_Pin = GPIO_Pin_6;
    GPIO_initstruct.GPIO_Mode = GPIO_Mode_AF;
    GPIO_initstruct.GPIO_OType = GPIO_OType_PP;
    GPIO_initstruct.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_initstruct.GPIO_Speed = GPIO_Speed_100MHz;
    GPIO_Init(GPIOC, &GPIO_initstruct);

    GPIO_PinAFConfig(GPIOC, GPIO_PinSource6, GPIO_AF_TIM3);

    // Timer base configuration (TIM3, 16 bit GP timer)
    TIM_TimeBaseInitTypeDef TIM_initstruct;
    TIM_initstruct.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_initstruct.TIM_Prescaler = 0;
    TIM_initstruct.TIM_Period = PWM_TICKS;
    TIM_initstruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM3, &TIM_initstruct);

    // PWM Channel 1 configuration
    TIM_OCInitTypeDef TIM_ocstruct;
    TIM_ocstruct.TIM_OCMode = TIM_OCMode_PWM1;
    TIM_ocstruct.TIM_OutputState = TIM_OutputState_Enable;
    TIM_ocstruct.TIM_Pulse = PWM_COMPARE_VALUE;
    TIM_ocstruct.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OC1Init(TIM3, &TIM_ocstruct);

    // Activate TIM3 preloads
    TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);
    TIM_ARRPreloadConfig(TIM3, ENABLE);

    TIM_Cmd(TIM3, ENABLE);
}